Optical system and image display device

Abstract

Provided are an optical system and an image display device capable of improving the utilization efficiency of image light from a display element. An optical system is provided with a light guide member (4) that guides image light as a virtual image to a field of view region of a user. The light guide member (4) has a diffraction structure region (61), which is a surface relief type diffraction grating, for dividing, in a first propagation direction, image light propagating in a first propagation direction intersecting the thickness direction of the main body section into a plurality of image light propagating in a second propagation direction intersecting the first propagation direction. The diffractive structure region (61) includes a first diffractive structure (611) and a second diffractive structure (612) located on the opposite side of the first diffractive structure (611) from the coupling region in the first propagation direction. The grating height of the first diffraction structure (611) is higher than the grating height of the second diffraction structure (612). The grating width of the first diffraction structure (611) is wider than the grating width of the second diffraction structure (612).

Description

Technical Field

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

[0002] Patent document 1 discloses an observation optical assembly (VOA) that presents a digital or virtual image to a visual recognizer as an image display device. The VOA includes a projector and an eyepiece worn by a visual recognizer. The eyepiece includes a plurality of eyepiece layers. Each eyepiece layer includes a plane waveguide, a coupling grating, an orthogonal pupil expansion region, and an exit pupil expansion region. The projector irradiates the image light toward the coupling grating of the eyepiece. The coupling grating couples the image light from the projector to the plane waveguide and propagates toward the orthogonal pupil expansion region. The plane waveguide propagates the image light in the horizontal direction by total reflection. The orthogonal pupil expansion region includes a diffraction element that copies the image light from the coupling grating and directs it toward the exit pupil expansion region. The exit pupil expansion region includes a diffraction element that causes a portion of the image light propagating in the plane waveguide to be emitted toward the eyes of the visual recognizer.

[0003] Prior Art Literature

[0004] Patent Literature

[0005] Patent Document 1: U.S. Patent Application Publication No. 2019-137777 Summary of the invention

[0006] -Problems to be solved by the invention-

[0007] Patent Document 1 discloses that in order to reduce the phenomenon that the amount of emitted light decreases due to position, in a diffractive structure, the height or depth of a diffraction element is changed as a function of position, thereby improving the uniformity of light.

[0008] However, since the image light has divergence, the image light has a deviation in the propagation angle (propagation angle) while being totally reflected in the waveguide. Since the light with the largest propagation angle and the light with the smallest propagation angle in the image light can exhibit different behaviors even for the same diffraction grating, in order to improve the utilization efficiency of the image light from the display element such as the projector, it is necessary to consider the deviation of the propagation angle. However, in Patent Document 1, such a deviation of the propagation angle is not considered.

[0009] The present disclosure provides an optical system and an image display device capable of improving the utilization efficiency of image light from a display element.

[0010] -Methods for solving problems-

[0011] An optical system according to one embodiment of the present disclosure includes: a light guide member that guides image light forming an image output from a display element to a user's field of view as a virtual image. The light guide member includes: a plate-shaped main body; a coupling region formed in the main body that allows image light to be incident on the main body so that the image light propagates in the main body; and a copy region formed in the main body and having a diffraction structure region as a surface relief type diffraction grating, which divides the image light propagating in the first propagation direction intersecting the thickness direction of the main body into a plurality of image lights propagating in the second propagation direction intersecting the first propagation direction. The diffraction structure region includes a first diffraction structure and a second diffraction structure located on the opposite side of the coupling region relative to the first diffraction structure in the first propagation direction. The grating height of the first diffraction structure is higher than the grating height of the second diffraction structure. The grating width of the first diffraction structure is wider than the grating width of the second diffraction structure.

[0012] An image display device according to one aspect of the present disclosure includes the above-mentioned optical system and a display element.

[0013] -Effects of the Invention-

[0014] The method disclosed in the present invention can improve the utilization efficiency of image light from a display element. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic perspective view of a configuration example of an image display device according to an embodiment.

[0016] Figure 2 yes Figure 1 A top view of a light guide component of an image display device.

[0017] Figure 3 yes Figure 1 A partial cross-sectional view of a light guide component of an image display device.

[0018] Figure 4 yes Figure 3 A graph of the diffraction efficiency characteristics of the first diffraction structure in the replication area.

[0019] Figure 5 yes Figure 3 A graph of the diffraction efficiency characteristics of the second diffraction structure in the replication area.

[0020] Figure 6 yes Figure 3 Graph of the diffraction efficiency characteristics of the third diffraction structure in the replication area.

[0021] Figure 7 is to use Figure 1 An explanatory diagram of an example of propagation of light in a light guide member of an image display device.

[0022] Figure 8 This is a partial cross-sectional view of the light guide member in Modification 1.

[0023] Fig. 9 This is a partial explanatory diagram of the light guide member in Modification Example 2.

[0024] Fig.10 This is a partial explanatory diagram of the light guide member in Modification Example 3.

[0025] Fig.11 This is a partial explanatory diagram of the light guide member in Modification Example 4.

[0026] Fig.12 This is a top view of the light guide member in Modification 5. DETAILED DESCRIPTION

[0027] The embodiments are described in detail below with appropriate reference to the drawings. However, unnecessary detailed descriptions are sometimes omitted. For example, detailed descriptions of known matters and repeated descriptions of substantially the same structures are sometimes omitted. This is to avoid the following description from becoming unnecessarily lengthy and to make it easy for those skilled in the art to understand. In addition, the inventors provide the drawings and the following descriptions in order to enable those skilled in the art to fully understand the present disclosure, and do not intend to limit the subject matter described in the claims.

[0028] Unless otherwise specified, the positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings. The figures described in the following embodiments are schematic diagrams, and the size and thickness ratios of the structural elements in the figures do not necessarily reflect the actual size ratios. In addition, the size ratios of the elements are not limited to the ratios shown in the drawings.

[0029] In the present disclosure, the expressions such as "light is directed toward the ○○ direction" and "propagates toward the ○○ direction" mean that the light forming the image is directed toward the ○○ direction as a whole, and the light rays included in the light forming the image may be inclined relative to the ○○ direction. For example, "light directed toward the ○○ direction" may mean that the main light ray of the light is directed toward the ○○ direction, or the secondary light ray of the light is inclined relative to the ○○ direction.

[0030] [1. Implementation Method]

[0031] [1.1 Structure]

[0032] Figure 1 1 is a schematic diagram of a configuration example of an image display device 1. The image display device 1 is mounted on the head of a user, for example, and is a head mounted display (HMD) that displays images (videos). Figure 1 As shown, the image display device 1 includes a display element 2 and an optical system 3 .

[0033] The display element 2 outputs image light L1 that forms an image in order to display an image (video). Figure 1 The image light L1 is depicted as light having directivity, but in fact it is incident on the optical system 3 as light having an angle corresponding to the viewing angle. 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 liquid crystal displays, organic EL displays, scanning MEMS mirrors, LCOS (Liquid Crystal On Silicon), DMD (Digital Mirror Device), and micro LEDs.

[0034] The optical system 3 guides the image light L1 output by the display element 2 to the visual field area 8 set for the user's eyes. In the visual field area 8, the user can visually recognize the image formed by the display element 2 with his own eyes without interruption. In particular, in the present embodiment, the optical system 3 expands the visual field area 8 through the effect of pupil expansion. That is, the optical system 3 expands the visual field area 8 by replicating the pupil of the image light L1. In the present embodiment, the visual field area 8 is defined by a rectangular plane.

[0035] like Figure 1 As shown, the optical system 3 includes a light guide member 4 and a projection optical system 7 .

[0036] The light guide member 4 guides the image light L1 forming the image output from the display element 2 to the visual field area 8 of the user as a virtual image.

[0037] like Figure 1 As shown, the light guide member 4 includes a main body 40 , a coupling region 5 , and a replication region 6 .

[0038] The main body 40 is formed of a material that is transparent in the visible light region. The main body 40 is in the shape of a plate. In the present embodiment, the main body 40 is in the shape of a rectangular plate. The main body 40 has a first surface 40a and a second surface 40b in the thickness direction of the main body 40. Figure 1 As shown, the main body 40 has a first surface 40 a disposed toward the display element 2 side, and a second surface 40 b disposed toward the viewing area 8 side.

[0039] Figure 2 4 is a top view of the light guide member 4 as viewed from the display element 2 side. Figure 2 As shown, the coupling region 5 and the replication region 6 are formed on the first surface 40 a of the main body 40 of the light guide member 4 .

[0040] The coupling region 5 allows the image light L1 to enter the main body 40, so that the image light L1 propagates in the main body 40. In the present embodiment, the coupling region 5 allows the image light L1 to enter the main body 40, so that the image light L1 propagates in the main body 40 in the first direction D1 ( Figure 2 In the present embodiment, the coupling region 5 is used for coupling between the display element 2 and the light guide member 4. The coupling region 5 allows the image light L1 to be incident on the main body 40, so that the image light L1 propagates in the main body 40 under the condition of total reflection. The "coupling" mentioned here refers to the state of propagating in the main body 40 of the light guide member 4 under the condition of total reflection.

[0041] The coupling region 5 is formed by a diffraction structure having a diffraction effect on the image light L1. The diffraction structure of the coupling region 5 is, for example, a transmissive surface relief diffraction grating, which periodically forms concavities and convexities. The diffraction structure of the coupling region 5 may include, for example, a diffraction structure in the second direction D2 ( Figure 2 The second direction D2 is a plurality of concave or convex portions extending in a downward direction (in a downward direction) and arranged at given intervals in the first direction D1, and the second direction D2 is orthogonal to the thickness direction of the main body 40 and intersects with the first direction D1. In the present disclosure, the "diffraction structure" can also be referred to as a "periodic structure" in which a plurality of concave or convex portions are periodically arranged. However, the "diffraction structure" sometimes includes an incomplete periodic structure in addition to the "periodic structure" due to other manufacturing constraints. In the present embodiment, the second direction D2 is also orthogonal to the first direction D1. The coupling region 5 causes the image light L1 to be incident on the main body 40 under the condition of total reflection relative to the first surface 40a and the second surface 40b through the diffraction effect. Through the coupling region 5, the image light L1 is totally reflected by the first surface 40a and the second surface 40b in the main body 40, thereby advancing in the first direction D1.

[0042] The size of the coupling region 5 is set so that part or all of the image light L1 from the display element 2 that has passed through the projection optical system 7 is incident on the coupling region 5. Figure 2 As shown, the coupling region 5 is in a quadrilateral shape.

[0043] The copy area 6 copies and expands the pupil of the image light L1 by dividing the image light L1 incident from the coupling area 5 into the main body 40 of the light guide member 4. In the present embodiment, the copy area 6 copies and expands the pupil of the image light L1 by dividing the image light L1 incident from the coupling area 5 into the main body 40 of the light guide member 4 into a plurality of image lights L3 advancing along the third direction D3 and emitting them to the field of view area 8. The third direction D3 is a direction from the light guide member 4 toward the field of view area 8. In the present embodiment, the third direction D3 is orthogonal to the first direction D1 and the second direction D2. In the present embodiment, the plurality of image lights L3 are parallel to each other. "The plurality of image lights L3 are parallel to each other" is not limited to the plurality of image lights L3 being parallel to each other in a strict sense, but also includes the plurality of image lights L3 being substantially parallel to each other. Even if the plurality of image lights L3 are not parallel to each other in a strict sense, it is sufficient as long as the directions of the plurality of image lights L3 are consistent to the extent that the plurality of image lights L3 are considered to be parallel in optical design. Since the plurality of image lights L3 are parallel to each other, the uniformity of the arrangement of the pupil of the image light in the viewing area 8 can be improved, thereby reducing omission of the pupil of the image light in the viewing area 8 .

[0044] Figure 2 The replication region 6 includes a first diffraction structure region 61 and a second diffraction structure region 62 .

[0045] The first diffraction structure region 61 is configured to be parallel to the coupling region 5 in the first direction D1. The first diffraction structure region 61 is a surface relief type diffraction grating that periodically forms projections and depressions. The first diffraction structure region 61 is a reflective type diffraction grating. The first diffraction structure region 61 is configured to divide the image light L1 propagating in the first propagation direction intersecting the thickness direction of the main body 40 into a plurality of image lights L2 propagating in the second propagation direction intersecting the first propagation direction. In the first diffraction structure region 61, the first direction D1 is the first propagation direction, and the second direction D2 is the second propagation direction. The first diffraction structure region 61 divides the image light L1 propagating in the main body 40 of the light guiding member 4 so that the plurality of image lights L2 arranged in the first direction D1 are directed toward the second diffraction structure region 62. In this way, the first diffraction structure region 61 expands the pupil of the image light L1 in the first direction D1. That is, as Figure 2 As shown, the first diffractive structure region 61 copies and expands the pupil of the image light L1 projected by the projection optical system 7 in the first direction D1 by dividing the image light L1 into a plurality of parallel image lights L2 heading toward the second diffractive structure region 62 .

[0046] The size of the first diffractive structure region 61 is set so that all the image light L1 from the coupling region 5 is incident on the first diffractive structure region 61. Figure 2 As shown, the first diffraction structure region 61 is a quadrilateral.

[0047] Figure 2 The first diffraction structure region 61 includes a first diffraction structure 611, a second diffraction structure 612, and a third diffraction structure 613. The second diffraction structure 612 is located on the opposite side of the coupling region 5 relative to the first diffraction structure 611 in the first direction D1. The third diffraction structure 613 is located on the opposite side of the first diffraction structure 611 relative to the second diffraction structure 612 in the first direction D1. In other words, the first diffraction structure 611, the second diffraction structure 612, and the third diffraction structure 613 are arranged in this order in the first direction D1.

[0048] like Figure 2 As shown, the first diffraction structure region 61 has a first end 61a on the coupling region 5 side in the first direction D1, and a second end 61b on the side opposite to the coupling region 5 in the first direction D1. The first diffraction structure 611 is located at least in a region R11 that occupies 1 / 4 of the first diffraction structure region 61 from the first end 61a of the first diffraction structure region 61 in the first direction D1. The second diffraction structure 612 is located at least in a region R12 that occupies 1 / 2 of the first diffraction structure region 61 from the first end 61a of the first diffraction structure region 61 in the first direction D1. The third diffraction structure 613 is located at least on the side opposite to the first diffraction structure 611 relative to the second diffraction structure 612 in the first direction D1, and is located in a region R13 that occupies 1 / 4 of the first diffraction structure region 61 from the second end 61b of the first diffraction structure region 61 in the first direction D1. As an example, in the first diffractive structure region 61 , the region R11 may be occupied by the first diffractive structure 611 , the region R13 may be occupied by the third diffractive structure 613 , and the area between the region R11 and the region R13 may be occupied by the second diffractive structure 612 .

[0049] Figure 3 4 is a partial cross-sectional view of the light guide member 4 of the image display device 1. In more detail, Figure 3 It is a cross-sectional view of a portion including the first diffractive structure region 61 in the light guide member 4 , taken along a plane including the periodic direction of the first diffractive structure region 61 and the thickness direction of the main body 40 .

[0050] like Figure 3As shown, the first diffraction structure region 61 is composed of concave-convex portions in the thickness direction relative to the main body 40, and the concave-convex portions are arranged to have periodicity in the periodic direction, that is, the concave-convex portions 611a of the first diffraction structure 611, the concave-convex portions 612a of the second diffraction structure 612, and the concave-convex portions 613a of the third diffraction structure 613. Figure 3 , the concavoconvex portions 611a, 612a, and 613a are convex portions protruding from the main body 40. The periodic direction is the direction in which the concavoconvex portions are arranged in a periodic manner. The periodic direction includes a component of the first propagation direction (the first direction D1 in the case of the first diffraction structure area 61). In order to convert the image light L1 propagating in the first direction D1 into the image light L2 propagating in the second direction D2, the periodic direction is set to a direction inclined relative to the first direction D1. The periodic direction is the direction of the wave number vector of the first diffraction structure area 61. As an example, the periodic direction of the first diffraction structure area 61 is a direction inclined 45 degrees relative to the first direction D1 in a plane orthogonal to the thickness direction of the main body 40. In this case, the concavoconvex portions 611a, 612a, and 613a extend along a direction inclined 45 degrees relative to the first direction D1 in a plane orthogonal to the thickness direction of the main body 40. Thus, the image light L1 propagating in the first direction D1 is converted into the image light L2 propagating in the second direction D2. The periodic direction is not limited to the direction inclined 45 degrees relative to the first direction D1 in the plane perpendicular to the thickness direction of the main body 40. For example, the angle of the periodic direction relative to the first direction D1 in the plane perpendicular to the thickness direction of the main body 40 may be 20 degrees to 70 degrees.

[0051] In the first diffraction structure region 61, the grating period is fixed. That is, the first diffraction structure 611, the second diffraction structure 612 and the third diffraction structure 613 have the same grating period. The grating period is the distance between the same positions of two adjacent concave-convex parts in the periodic direction. The grating period of the first diffraction structure 611 is the distance between the same positions of two adjacent concave-convex parts 611a in the periodic direction. The grating period of the second diffraction structure 612 is the distance between the same positions of two adjacent concave-convex parts 612a in the periodic direction. The grating period of the third diffraction structure 613 is the distance between the same positions of two adjacent concave-convex parts 613a in the periodic direction. As examples of the distance between the same positions of adjacent concave-convex parts in the periodic direction, the distance between the front ends of adjacent concave-convex parts in the periodic direction, the distance between the centers of adjacent concave-convex parts in the periodic direction, and the distance between the rear ends of adjacent concave-convex parts in the periodic direction can be cited.

[0052] As described above, the first diffraction structure 611, the second diffraction structure 612, and the third diffraction structure 613 have the same grating period, but have different diffraction efficiency characteristics because at least one of the grating height and the grating width is different. Here, the grating height is the height of the concave-convex portion (concave-convex portion 611a, 612a, 613a). The grating width is the width of the concave-convex portion (concave-convex portion 611a, 612a, 613a). The width of the concave-convex portion is not so much the width of the front end side ( Figure 3 The width of the upper end side of the concave-convex portion is better to be said to be the base end side (the main body 40 side, Figure 3 The width of the lower end side).

[0053] Next, refer to Figure 3 The grating height and grating width of the first diffractive structure 611 , the second diffractive structure 612 , and the third diffractive structure 613 in this embodiment will be described.

[0054] like Figure 3 As shown, the grating height (the height of the concavo-convex portion 611a) of the first diffraction structure region 61 is set to Ha, and the grating height (the height of the concavo-convex portion 612a) of the second diffraction structure 612 is set to Hb, then the grating height Ha and the grating height Hb satisfy the relationship of Ha>Hb. That is, the grating height Ha of the first diffraction structure 611 is higher than the grating height Hb of the second diffraction structure 612. The grating width (the width of the concavo-convex portion 611a) of the first diffraction structure region 61 is set to Wa, and the grating width (the width of the concavo-convex portion 612a) of the second diffraction structure 612 is set to Wb, then the grating width Wa and the grating width Wb satisfy the relationship of Wa>Wb. That is, the grating width Wa of the first diffraction structure 611 is wider than the grating width Wb of the second diffraction structure 612.

[0055] To summarize the above, the first diffractive structure region 61 satisfies the following mathematical expressions (1) and (2): Thus, the utilization efficiency of the image light L1 from the display element 2 can be improved.

[0056] [Mathematical formula 1]

[0057] Ha>Hb (1)

[0058] [Mathematical formula 2]

[0059] Wa>Wb (2)

[0060] Furthermore, if Figure 3As shown, the grating period of the first diffraction structure region 61 can be set to T, and the grating height of the first diffraction structure 611 (the height of the concavo-convex portion 611a) can be set to Ha, then the grating period T and the grating height Ha satisfy the relationship of 0.3<Ha / T<1.2. The grating width of the first diffraction structure 611 (the width of the concavo-convex portion 611a) is set to Wa, then the grating period T and the grating width Wa satisfy the relationship of 0.7<Wa / T<1.0. The grating height of the second diffraction structure 612 (the height of the concavo-convex portion 612a) is set to Hb, then the grating height Ha and the grating height Hb satisfy the relationship of 1.2<Ha / Hb<10.0.

[0061] To summarize the above, the first diffractive structure region 61 satisfies the following mathematical expressions (3) to (5).

[0062] [Mathematical formula 3]

[0063]

[0064] [Formula 4]

[0065]

[0066] [Formula 5]

[0067]

[0068] The first diffraction structure region 61 satisfies at least the above formulas (1) and (2), so that the first diffraction structure 611 of the first diffraction structure region 61 can have Figure 4 The first diffraction structure region 61 preferably satisfies the above-mentioned formulas (3) to (5) in addition to the above-mentioned formulas (1) and (2). Figure 4 6 is a graph showing the diffraction efficiency characteristics of the first diffraction structure 611 of the first diffraction structure region 61 of the replication region 6. Figure 4 In FIG. 1 , the horizontal axis is the propagation angle [°], and the vertical axis is the diffraction efficiency. The propagation angle is the incident angle of the image light L1 propagating in the first direction D1 with respect to the interface (the first surface 40a or the second surface 40b) of the main body 40. Figure 4 , the first diffraction structure 611 has a diffraction efficiency characteristic in which the diffraction efficiency increases as the propagation angle increases. In other words, the first diffraction structure 611 has a diffraction efficiency characteristic in which the diffraction efficiency decreases as the propagation angle decreases. Figure 4 middle, is the maximum value of the propagation angle, is the minimum value of the propagation angle. Ea1 is the propagation angle When the diffraction efficiency is That is, when the diffraction efficiency of the light propagating along the first direction D1 with respect to the interface of the main body 40 being the largest is set to Ea1, and the diffraction efficiency of the light propagating along the first direction D1 with respect to the interface of the main body 40 being the smallest is set to Ea2, the first diffraction structure 611 has a diffraction efficiency characteristic satisfying the relationship of Ea1>Ea2.

[0069] The first diffraction structure region 61 satisfies the above formulas (1) and (2), so that the second diffraction structure 612 of the first diffraction structure region 61 can have Figure 5 The first diffraction structure region 61 preferably satisfies the above-mentioned formulas (3) to (5) in addition to the above-mentioned formulas (1) and (2). Figure 5 6 is a graph showing the diffraction efficiency characteristics of the second diffraction structure 612 of the first diffraction structure region 61 of the replication region 6. Figure 5 In the figure, the horizontal axis is the propagation angle [°] and the vertical axis is the diffraction efficiency. Figure 5 The second diffraction structure 612 has a diffraction efficiency characteristic in which the diffraction efficiency changes in a parabolic shape with respect to the propagation angle. Figure 5 middle, is the maximum value of the propagation angle, is the minimum value of the propagation angle. Eb1 is the propagation angle When the diffraction efficiency is That is, let Eb1 be the diffraction efficiency of the light whose incident angle (propagation angle) relative to the interface of the main body 40 is the largest among the light propagating along the first direction D1, and let Eb2 be the diffraction efficiency of the light whose incident angle (propagation angle) relative to the interface of the main body 40 is the smallest among the light propagating along the first direction D1, then the second diffraction structure 612 has a diffraction efficiency characteristic that satisfies the relationship of Eb1 ≥ Eb2. In particular, Figure 5 In the figure, the diffraction efficiencies Eb1 and Eb2 satisfy the relationship Eb1=Eb2.

[0070] When the grating height of the third diffractive structure 613 is Hc, the grating heights Ha, Hb, and Hc satisfy the relationship of Ha<Hc and the relationship of Hb<Hc. When the grating width of the third diffractive structure 613 is Wc, the grating widths Wa, Wb, and Wc satisfy the relationship of Wc<Wa and the relationship of Wc<Wb.

[0071] To summarize the above, the first diffractive structure region 61 satisfies the following mathematical expressions (6) to (9).

[0072] [Mathematical formula 6]

[0073] Ha<Hc (6)

[0074] [Mathematical formula 7]

[0075] Hb<Hc (7)

[0076] [Mathematical formula 8]

[0077] Wc<Wa (8)

[0078] [Mathematical formula 9]

[0079] Wc<Wb (9)

[0080] The first diffraction structure region 61 satisfies the above formulas (1) to (9), so that the third diffraction structure 613 of the first diffraction structure region 61 can have Figure 6 Diffraction efficiency characteristics are shown. Figure 6 6 is a graph showing the diffraction efficiency characteristics of the third diffraction structure 613 of the first diffraction structure region 61 of the replication region 6. Figure 6 In the figure, the horizontal axis is the propagation angle [°] and the vertical axis is the diffraction efficiency. Figure 6 , the third diffraction structure 613 has a diffraction efficiency characteristic that the diffraction efficiency decreases as the propagation angle increases. In other words, the third diffraction structure 613 has a diffraction efficiency characteristic that the diffraction efficiency increases as the propagation angle decreases. Figure 6 middle, is the maximum value of the propagation angle, is the minimum value of the propagation angle. Ec1 is the propagation angle When the diffraction efficiency is That is, when the diffraction efficiency of the light propagating along the first direction D1 with respect to the interface of the main body 40 being the largest is set to Ec1, and the diffraction efficiency of the light propagating along the first direction D1 with respect to the interface of the main body 40 being the smallest is set to Ec2, the third diffraction structure 613 has a diffraction efficiency characteristic satisfying the relationship of Ec1<Ec2.

[0081] In this embodiment, as an example, T = 320nm, Ha = 200nm, Wa = 300nm, Hb = 100nm, Wb = 160nm, Hc = 250nm, Wc = 180nm. That is, Ha>Hb, satisfying mathematical formula (1). Wa>Wb, satisfying mathematical formula (2). Ha / T = 0.625, satisfying mathematical formula (3). Wa / T = 0.9375, satisfying mathematical formula (4). Ha / Hb = 2, satisfying mathematical formula (5). It is clear that the above numerical values ​​satisfy mathematical formulas (6) to (9).

[0082] In this embodiment, if Figure 3As shown, the central axis C1 of the concavo-convex portion 611a in the first diffractive structure 611 is inclined relative to the thickness direction T1 of the main body 40. The central axis C1 is an axis passing through the center of the concavo-convex portion 611a in a plane including the periodic direction of the first diffractive structure region 61 and the thickness direction T1 of the main body 40 when the width Wa of the concavo-convex portion 611a is set to be fixed. In this embodiment, the inclination angle of the central axis C1 of the concavo-convex portion 611a relative to the thickness direction T1 of the main body 40 is equal to the surface ( Figure 3 The inclination angles of the left side (in the figure) relative to the thickness direction T1 of the main body 40 are equal.

[0083] In the first diffraction structure region 61, the central axis C1 of the concavoconvex portion 611a is inclined relative to the thickness direction T1 of the main body 40, so that the diffraction efficiency of light in a given plane orthogonal to the thickness direction T1 of the main body 40 can be controlled. For example, by adjusting the direction and angle at which the central axis C1 of the concavoconvex portion 611a is inclined relative to the thickness direction T1 of the main body 40, the amount of light propagating in the direction of diffraction of unnecessary light can be reduced, and the amount of light propagating in the direction of diffraction of necessary light can be increased. Thus, the image light L1 from the display element 2 can be effectively guided to the field of view region 8. Therefore, the utilization efficiency of the image light L1 from the display element 2 can be improved.

[0084] In this embodiment, if Figure 3 As shown, the central axis C2 of the concavo-convex portion 612a in the second diffractive structure 612 is inclined relative to the thickness direction T1 of the main body 40. The central axis C2 is an axis passing through the center of the concavo-convex portion 612a in a plane including the periodic direction of the first diffractive structure region 61 and the thickness direction of the main body 40 when the width Wb of the concavo-convex portion 612a is set to be fixed. In this embodiment, the inclination angle of the central axis C2 of the concavo-convex portion 612a relative to the thickness direction T1 of the main body 40 is the same as the surface ( Figure 3 The inclination angles of the left side (in the figure) relative to the thickness direction T1 of the main body 40 are equal.

[0085] In the first diffraction structure region 61, the central axis C2 of the concavoconvex portion 612a is inclined relative to the thickness direction T1 of the main body 40, so that the diffraction efficiency of light in a given plane orthogonal to the thickness direction T1 of the main body 40 can be controlled. For example, by adjusting the direction and angle at which the central axis C2 of the concavoconvex portion 612a is inclined relative to the thickness direction T1 of the main body 40, the amount of light propagating in the direction of diffraction of unnecessary light can be reduced, and the amount of light propagating in the direction of diffraction of necessary light can be increased. Thus, the image light L1 from the display element 2 can be effectively guided to the field of view region 8. Therefore, the utilization efficiency of the image light L1 from the display element 2 can be improved.

[0086] Here, if the diffraction efficiency characteristics of each of the first diffraction structure 611 and the second diffraction structure 612 are considered, the inclination angle of the central axis C1 of the concavoconvex portion 611a in the first diffraction structure 611 relative to the thickness direction T1 of the main body 40 and the inclination angle of the central axis C2 of the concavoconvex portion 612a in the second diffraction structure 612 relative to the thickness direction T1 of the main body 40 can satisfy the following relationship. That is, the inclination angle of the central axis C1 of the concavoconvex portion 611a in the first diffraction structure 611 relative to the thickness direction T1 of the main body 40 is set to θa, and the inclination angle of the central axis C2 of the concavoconvex portion 612a in the second diffraction structure 612 relative to the thickness direction T1 of the main body 40 is set to θb, then the inclination angles θa and θb satisfy the relationship of 0.9<θa / θb<1.1. As an example, θa is set to be greater than 20 degrees and less than 65 degrees.

[0087] In this embodiment, if Figure 3 As shown, the central axis C3 of the concavo-convex portion 613a in the third diffractive structure 613 is inclined relative to the thickness direction T1 of the main body 40. The central axis C3 is an axis passing through the center of the concavo-convex portion 613a in a plane including the periodic direction of the first diffractive structure region 61 and the thickness direction of the main body 40 when the width Wc of the concavo-convex portion 613a is set to be fixed. In this embodiment, the inclination angle of the central axis C3 of the concavo-convex portion 613a relative to the thickness direction T1 of the main body 40 is the same as the surface ( Figure 3 The inclination angles of the left side (in the figure) relative to the thickness direction T1 of the main body 40 are equal.

[0088] In the first diffraction structure region 61, the central axis C3 of the concavoconvex portion 613a is inclined relative to the thickness direction T1 of the main body 40, so that the diffraction efficiency of light in a given plane orthogonal to the thickness direction T1 of the main body 40 can be controlled. For example, by adjusting the direction and angle at which the central axis C3 of the concavoconvex portion 613a is inclined relative to the thickness direction T1 of the main body 40, the amount of light propagating in the direction of diffraction of unnecessary light can be reduced, and the amount of light propagating in the direction of diffraction of necessary light can be increased. Thus, the image light L1 from the display element 2 can be effectively guided to the field of view region 8. Therefore, the utilization efficiency of the image light L1 from the display element 2 can be improved.

[0089] Here, if the diffraction efficiency characteristics of each of the first diffraction structure 611 and the third diffraction structure 613 are considered, the inclination angle of the central axis C1 of the concavo-convex portion 611a in the first diffraction structure 611 with respect to the thickness direction T1 of the main body 40 and the inclination angle of the central axis C2 of the concavo-convex portion 612a in the third diffraction structure 613 with respect to the thickness direction T1 of the main body 40 can satisfy the following relationship. That is, when the inclination angle of the central axis C1 of the concavo-convex portion 611a in the first diffraction structure 611 with respect to the thickness direction T1 of the main body 40 is set to θa, and the inclination angle of the central axis C3 of the concavo-convex portion 613a in the third diffraction structure 613 with respect to the thickness direction T1 of the main body 40 is set to θc, the inclination angles θa and θc satisfy the relationship of 0.9<θa / θc<1.1.

[0090] In this embodiment, if Figure 3 As shown, the concavoconvex portion 611a in the first diffractive structure 611 has the following shape: in the thickness direction T1 of the main body 40, the distance between the concavoconvex portions 611a in the periodic direction of the first diffractive structure region 61 increases as it moves from the inside of the main body 40 toward the outside. The concavoconvex portion 611a is a so-called wedge-shaped. In other words, the space 611b between the concavoconvex portions 611a in the thickness direction T1 of the main body 40, the size of the periodic direction of the first diffractive structure region 61 increases as it moves from the inside of the main body 40 toward the outside. That is, the base end side ( Figure 3 The distance G11 between the concave-convex parts 611a located at the lower end side of the concave-convex part 611a is greater than that located at the front end side of the concave-convex part 611a ( Figure 3 The distance G12 between the concave and convex parts 611a (on the upper end side) is short.

[0091] In this embodiment, if Figure 3 As shown, the concavoconvex portion 612a in the second diffractive structure 612 has the following shape: in the thickness direction T1 of the main body 40, the distance between the concavoconvex portions 612a in the periodic direction of the first diffractive structure region 61 increases as it moves from the inside of the main body 40 toward the outside. The concavoconvex portion 612a is a so-called wedge-shaped. In other words, the space 612b between the concavoconvex portions 612a in the periodic direction of the first diffractive structure region 61 increases in size as it moves from the inside of the main body 40 toward the outside in the thickness direction T1 of the main body 40. That is, the base end side ( Figure 3 The distance G21 between the concave-convex parts 612a located at the lower end side of the concave-convex part 612a is greater than that located at the front end side of the concave-convex part 612a ( Figure 3 The distance G22 between the concave and convex parts 612a (on the upper end side) is short.

[0092] In this embodiment, if Figure 3As shown, the concavoconvex portion 613a in the third diffractive structure 613 has the following shape: in the thickness direction T1 of the main body 40, the distance between the concavoconvex portions 613a in the periodic direction of the first diffractive structure region 61 increases as it moves from the inside of the main body 40 toward the outside. The concavoconvex portion 613a is a so-called wedge-shaped. In other words, the space 613b between the concavoconvex portions 613a in the thickness direction T1 of the main body 40, the size of the periodic direction of the first diffractive structure region 61 increases as it moves from the inside of the main body 40 toward the outside. That is, the base end side ( Figure 3 The distance G31 between the concave-convex parts 613a located at the lower end side of the concave-convex part 613a is greater than that located at the front end side of the concave-convex part 613a ( Figure 3 The distance G32 between the concave and convex parts 613a (on the upper end side) is short.

[0093] The second diffraction structure region 62 is configured to be parallel to the first diffraction structure region 61 in the second direction D2. The second diffraction structure region 62 is a surface relief type diffraction grating that periodically forms concavities and convexities. The second diffraction structure region 62 is a transmission type diffraction grating. The second diffraction structure region 62 is configured to divide the image light L2 propagating in the first propagation direction intersecting the thickness direction of the main body 40 into a plurality of image lights L3 propagating in the second propagation direction intersecting the first propagation direction. In the second diffraction structure region 62, the second direction D2 is the first propagation direction, and the third direction D3 ( Figure 1 The second diffraction structure area 62 divides the image light L2 propagating in the main body 40 of the light guide member 4, thereby directing a plurality of image lights L3 arranged in the second direction D2 toward the field of view area 8. In this way, the second diffraction structure area 62 expands the pupil of the image light L1 in the second direction D2. That is, Figure 1 As shown, the second diffraction structure area 62 copies and expands the pupil of the image light L1 projected by the projection optical system 7 in the second direction D2 by dividing the image light L2 into a plurality of parallel image lights L3 directed toward the field of view area 8. The second diffraction structure area 62 is used as an emission structure for causing the image light L1 incident on the main body 40 to be emitted from the main body 40 toward the field of view area 8 through the coupling area 5.

[0094] The size of the second diffractive structure region 62 is set so that all the light L2 from the first diffractive structure region 61 is incident on the second diffractive structure region 62. Figure 2 As shown, the second diffractive structure region 62 is a quadrilateral. The second diffractive structure region 62 may include, for example, a plurality of concave portions or convex portions extending in the first direction D1 and arranged at a given interval in the second direction D2.

[0095] The projection optical system 7 projects the image light L1 that forms the image output from the display element 2. Thus, the projection optical system 7 causes the image light L1 from the display element 2 to be incident on the light guide member 4. Figure 1 As shown, the projection optical system 7 is located between the display element 2 and the coupling region 5 of the light guide member 4. The projection optical system 7, for example, collimates the image light L1 from the display element 2 and makes it incident on the coupling region 5. The projection optical system 7 makes the image light L1 incident on the coupling region 5 as substantially collimated light. The projection optical system 7 is, for example, a biconvex lens.

[0096] [1.2 Function]

[0097] Next, the function of the light guide member 4 , particularly the transfer area 6 , of the image display device 1 according to the present embodiment will be described. Figure 7 This is an explanatory diagram of an example of propagation of light by the light guide member 4 of the image display device 1 .

[0098] The image light L1 from the display element 2 is incident on the coupling region 5 of the light guide member 4, and the coupling region 5 directs the image light L1 toward the copy region 6. Figure 7 As shown, the image light L1 includes a principal ray L11 corresponding to the center of the virtual image, and a plurality of secondary rays L12 and L13 approaching the principal ray L11 as they move from the projection optical system 7 toward the coupling region 5. Figure 7 In order to distinguish the main ray L11, the secondary ray L12, and the secondary ray L13 from each other, the main ray L11 is represented by a solid arrow, the secondary ray L12 is represented by a dotted arrow, and the secondary ray L13 is represented by a dashed arrow. Figure 7 In the figure, the auxiliary light beam L12 corresponds to the light whose incident angle (propagation angle) with respect to the interface of the main body 40 is the largest among the image light beams L1. Figure 7 Among them, the auxiliary light beam L13 corresponds to the light whose incident angle (propagation angle) with respect to the interface of the main body portion 40 is the smallest among the image light beams L1.

[0099] The principal light ray L11 and the secondary light rays L12 and L13 of the image light L1 are totally reflected by the first surface 40a and the second surface 40b in the main body 40 of the light guide member 4, and thus advance along the first direction D1 and reach the first diffraction structure region 61 of the copy region 6. In the first diffraction structure region 61, the first diffraction structure 611, the second diffraction structure 612, and the third diffraction structure 613 are arranged in this order in the first direction D1.

[0100] The principal light ray L11 and the secondary light rays L12 and L13 first reach the first diffraction structure 611. A portion of the principal light ray L11 and the secondary light rays L12 and L13 passes through the first diffraction structure 611 toward the second diffraction structure region 62, passes through the second diffraction structure region 62, and is taken out as emitted light L11a, L12a, and L13a. The remaining portion of the principal light ray L11 and the secondary light rays L12 and L13 that is not diffracted by the first diffraction structure 611 reaches the second diffraction structure 612. A portion of the principal light ray L11 and the secondary light rays L12 and L13 passes through the second diffraction structure 612 toward the second diffraction structure region 62, passes through the second diffraction structure region 62, and is taken out as emitted light L11b, L12b, and L13b. The remaining part of the main light ray L11 and the auxiliary light rays L12 and L13 that is not diffracted by the second diffraction structure 612 reaches the third diffraction structure 613. A part of the main light ray L11 and the auxiliary light rays L12 and L13 passes through the third diffraction structure 613 toward the second diffraction structure area 62, passes through the second diffraction structure area 62, and is taken out as emitted light L11c, L12c, and L13c.

[0101] exist Figure 7 In FIG. 1 , the light amounts of the emitted light L11 a to L11 c , L12 a to L12 c , and L13 a to L13 c are schematically shown by the thickness of the corresponding arrow lines.

[0102] exist Figure 7 In the embodiment, the emitted light 13a does not reach the visual field area 8, so it is wasted. Figure 4 As shown, the first diffraction structure 611 has a diffraction efficiency characteristic that satisfies the relationship of Ea1>Ea2. Therefore, among the main light L11 and the secondary light rays L12 and L13, the secondary light ray L13 is more difficult to diffract than the secondary light ray L12. That is, the secondary light ray L13 is more difficult to be directed toward the second diffraction structure area 62 side than the secondary light ray L12, and as a result, it is difficult to be taken out from the main body 40 to the outside through the second diffraction structure area 62. In other words, the first diffraction structure 611 can reduce the amount of the emitted light L13a that does not reach the visual field area 8 in the first direction D1. Therefore, the utilization efficiency of the image light L1 from the display element 2 can be improved. On the other hand, the secondary light ray L12 is more likely to be directed toward the second diffraction structure area 62 side than the secondary light ray L13, and as a result, it is easy to be taken out from the main body 40 to the outside through the second diffraction structure area 62. In other words, the first diffraction structure 611 can increase the amount of the emitted light L12a that reaches the visual field area 8 in the first direction D1. Therefore, it is possible to improve the utilization efficiency of the image light L1 from the display element 2. In addition, it is possible to reduce the amount of the secondary light beam L12 that passes through the first diffraction structure region 61 without being diffracted.

[0103] exist Figure 7In the embodiment, the emitted light L11b, L12b, L13b will not be wasted because they reach the visual field area 8. Figure 5 As shown, the second diffraction structure 612 has a diffraction efficiency characteristic that satisfies the relationship Eb1=Eb2. Therefore, the second diffraction structure 612 can reduce the deviation of the light amount of the emitted light L11b, L12b, and L13b in the first direction D1. Furthermore, the amount of the secondary light ray L13 taken out from the main body 40 is limited in the first diffraction structure 611, but in the second diffraction structure 612, the amount limited in the first diffraction structure 611 can be compensated, thereby reducing the amount of the secondary light ray L13 that is not diffracted by the first diffraction structure area 61 and passes through. In addition, the amount of the secondary light ray L12 that is not diffracted by the first diffraction structure area 61 and passes through can be reduced.

[0104] In this embodiment, if Figure 6 As shown, the third diffraction structure 613 has a diffraction efficiency characteristic that satisfies the relationship Ec1<Ec2. Therefore, among the main light L11 and the secondary light rays L12 and L13, the secondary light ray L13 is easier to diffract than the secondary light ray L12. That is, the secondary light ray L13 is easier to be directed toward the second diffraction structure area 62 side than the secondary light ray L12, and as a result, it is easy to be taken out from the main body 40 to the outside through the second diffraction structure area 62. The amount of the secondary light ray L13 taken out from the main body 40 is limited in the first diffraction structure 611, but in the third diffraction structure 613, the amount limited in the first diffraction structure 611 can also be compensated, thereby reducing the amount of the secondary light ray L13 passing through the first diffraction structure area 61. As a result, the amount of the emitted light L13c reaching the field of view area 8 in the first direction D1 can be increased. Therefore, the utilization efficiency of the image light L1 from the display element 2 can be improved. In the third diffraction structure 613 , the secondary ray L12 is more difficult to diffract than the secondary ray L13 , but the secondary ray L13 is diffracted by the first diffraction structure 611 and the second diffraction structure 612 before reaching the third diffraction structure 613 , so the influence is small.

[0105] [1.3 Effects, etc.]

[0106] The optical system 3 described above includes: a light guide member 4 that guides the image light L1 forming the image output from the display element 2 to the user's visual field area 8 as a virtual image. The light guide member 4 includes: a plate-shaped main body 40; a coupling region 5 formed in the main body 40 that allows the image light L1 to enter the main body 40 so that the image light L1 propagates in the main body 40; and a copy region 6 formed in the main body 40 and having a first diffraction structure region 61 as a surface relief type diffraction grating, the first diffraction structure region 61 splits the image light L1 propagating in the first propagation direction (first direction D1) intersecting the thickness direction T1 of the main body 40 into a plurality of image lights L2 propagating in the second propagation direction (second direction D2) intersecting the first propagation direction. The first diffraction structure region 61 includes a first diffraction structure 611 and a second diffraction structure 612 located on the opposite side of the coupling region 5 with respect to the first diffraction structure 611 in the first propagation direction. The grating height of the first diffractive structure 611 is higher than the grating height of the second diffractive structure 612. The grating width of the first diffractive structure 611 is wider than the grating width of the second diffractive structure 612. This structure can improve the utilization efficiency of the image light L1 from the display element 2.

[0107] In the optical system 3, the diffraction structure region 61 satisfies the relationship of 0.3<Ha / T<1.2, 0.7<Wa / T<1.0 and 1.2<Ha / Hb<10.0. T is the grating period of the first diffraction structure region 61. Ha is the grating height of the first diffraction structure 611. Wa is the grating width of the first diffraction structure 611. Hb is the grating height of the second diffraction structure 612. This structure can improve the utilization efficiency of the image light L1 from the display element 2.

[0108] In the optical system 3, the first diffraction structure 611 has the following diffraction efficiency characteristics: the diffraction efficiency of the light (secondary light ray L12) whose incident angle with respect to the interface of the main body 40 is the largest among the light (image light L1) propagating in the first propagation direction is greater than the diffraction efficiency of the light (secondary light ray L13) whose incident angle with respect to the interface of the main body 40 is the smallest among the light (image light L1) propagating in the first propagation direction. This structure can further improve the utilization efficiency of the image light L1 from the display element 2.

[0109] In the optical system 3, the second diffraction structure 612 has the following diffraction efficiency characteristics: the diffraction efficiency of the light (secondary light ray L12) whose incident angle with respect to the interface of the main body 40 is the largest among the light (image light L1) propagating in the first propagation direction is greater than the diffraction efficiency of the light (secondary light ray L13) whose incident angle with respect to the interface of the main body 40 is the smallest among the light (image light L1) propagating in the first propagation direction. This structure can further improve the utilization efficiency of the image light L1 from the display element 2.

[0110] In the optical system 3, the first diffraction structure region 61 also includes a third diffraction structure 613. The third diffraction structure 613 is located on the opposite side of the first diffraction structure 611 relative to the second diffraction structure 612 in the first propagation direction. The first diffraction structure region 61 satisfies both the relationship of Ha<Hc and the relationship of Hb<Hc. Ha is the grating height of the first diffraction structure 611. Hb is the grating height of the second diffraction structure 612. Hc is the grating height of the third diffraction structure 613. This structure can further improve the utilization efficiency of the image light L1 from the display element 2.

[0111] In the optical system 3 , the first diffractive structure region 61 satisfies both the relationship of Wc<Wa and the relationship of Wc<Wb. Wc is the grating width of the third diffractive structure 613. This configuration can further improve the utilization efficiency of the image light L1 from the display element 2.

[0112] In the optical system 3, the third diffraction structure 613 has the following diffraction efficiency characteristics: the diffraction efficiency of the light (secondary light ray L12) whose incident angle with respect to the interface of the main body 40 is the largest among the light (image light L1) propagating in the first propagation direction is smaller than the diffraction efficiency of the light (secondary light ray L13) whose incident angle with respect to the interface of the main body 40 is the smallest among the light (image light L1) propagating in the first propagation direction. This structure can further improve the utilization efficiency of the image light L1 from the display element 2.

[0113] In the optical system 3, the first diffractive structure region 61 is composed of concavoconvex parts 611a, 612a, 613a relative to the thickness direction T1 of the main body 40, and the concavoconvex parts 611a, 612a, 613a are arranged to have periodicity in the periodic direction including the component of the first propagation direction. The central axis C1 of the concavoconvex part 611a in the first diffractive structure 611 is inclined relative to the thickness direction T1 of the main body 40. This structure can further improve the utilization efficiency of the image light L1 from the display element 2.

[0114] In the optical system 3, the concavoconvex parts 611a in the first diffractive structure 611 have a shape in which the distance between the concavoconvex parts 611a in the periodic direction increases from the inside to the outside of the main body 40 in the thickness direction T1 of the main body 40. This structure can facilitate the manufacture of the light guide member 4.

[0115] In the optical system 3, the central axis C2 of the concavo-convex portion 612a in the second diffractive structure 612 is inclined with respect to the thickness direction T1 of the main body 40. This structure can further improve the utilization efficiency of the image light L1 from the display element 2.

[0116] In the optical system 3, the inclination angle of the central axis C1 of the concavo-convex portion 611a in the first diffractive structure 611 with respect to the thickness direction T1 of the main body 40 is set to θa, and the inclination angle of the central axis C2 of the concavo-convex portion 612a in the second diffractive structure 612 with respect to the thickness direction T1 of the main body 40 is set to θb, and the relationship of 0.9<θa / θb<1.1 is satisfied. This structure can further improve the utilization efficiency of the image light L1 from the display element 2.

[0117] In the optical system 3, the central axis C3 of the concavo-convex portion 613a in the third diffractive structure 613 is inclined with respect to the thickness direction T1 of the main body 40. This structure can further improve the utilization efficiency of the image light L1 from the display element 2.

[0118] In the optical system 3, the inclination angle of the central axis C1 of the concavo-convex portion 611a in the first diffractive structure 611 with respect to the thickness direction T1 of the main body 40 is set to θa, and the inclination angle of the central axis C3 of the concavo-convex portion 613a in the third diffractive structure 613 with respect to the thickness direction T1 of the main body 40 is set to θc, and the relationship of 0.9<θa / θc<1.1 is satisfied. This structure can further improve the utilization efficiency of the image light L1 from the display element 2.

[0119] In the optical system 3, the copy area 6 has an emission structure (second diffraction structure area 62) that emits the image light L1 incident on the main body 40 from the main body 40 toward the field of view area 8 through the coupling area 5. Since this structure does not require the emission structure to be provided independently of the copy area 6, the light guide member 4 can be miniaturized.

[0120] In the optical system 3, the first diffractive structure region 61 has a first end 61a on the coupling region 5 side in the first propagation direction, and a second end 61b on the side opposite to the coupling region 5 in the first propagation direction. The first diffractive structure 611 is located at least in a region R11 that occupies 1 / 4 of the first diffractive structure region 61 from the first end 61a of the first diffractive structure region 61 in the first propagation direction. This structure can further improve the utilization efficiency of the image light L1 from the display element 2.

[0121] In the optical system 3 , the second diffractive structure 612 is located at least in a region R12 occupying 1 / 2 of the first diffractive structure region 61 from the first end 61a of the first diffractive structure region 61 in the first propagation direction. This structure can further improve the utilization efficiency of the image light L1 from the display element 2 .

[0122] In the optical system 3, the third diffractive structure 613 is located on the side opposite to the first diffractive structure 611 with respect to the second diffractive structure 612 at least in the first propagation direction, and is located in a region R13 occupying 1 / 4 of the first diffractive structure region 61 from the second end 61b of the first diffractive structure region 61 in the first propagation direction. This structure can further improve the utilization efficiency of the image light L1 from the display element 2.

[0123] The optical system 3 further includes a projection optical system 7 that causes the image light L1 to enter the coupling region 5 of the light guide member 4 as substantially collimated light. This configuration can further improve the utilization efficiency of the image light L1 from the display element 2.

[0124] The image display device 1 described above includes the optical system 3 and the display element 2. This structure can improve the utilization efficiency of the image light L1 from the display element 2.

[0125] [2. Modifications]

[0126] The embodiments of the present disclosure are not limited to the above-mentioned embodiments. As long as the above-mentioned embodiments can achieve the subject of the present disclosure, various changes can be made according to the design, etc. The following lists the modified examples of the above-mentioned embodiments. The modified examples described below can be appropriately combined and applied.

[0127] [2.1 Modification 1]

[0128] Figure 8 4A is a partial cross-sectional view of the light guide member 4A in the modification example 1. In more detail, Figure 8 It is a cross-sectional view of a portion including the first diffractive structure region 61A of the transfer region 6A in the light guide member 4A.

[0129] Figure 8 The first diffraction structure region 61A and Figure 3 Similarly, the first diffraction structure region 61 includes a first diffraction structure 611 , a second diffraction structure 612 , and a third diffraction structure 613 . Figure 8 The shape and size of the concavo-convex portion of the first diffractive structure region 61A, that is, the shape and size of the concavo-convex portion 611a of the first diffractive structure 611, the concavo-convex portion 612a of the second diffractive structure 612, and the concavo-convex portion 613a of the third diffractive structure 613 are the same as Figure 3 The first diffraction structure region 61 is different.

[0130] In this modified example, T=320 nm, Ha=100 nm, Wa=250 nm, Hb=60 nm, Wb=160 nm, Hc=200 nm, and Wc=160 nm.

[0131] Ha>Hb, satisfying equation (1). Wa>Wb, satisfying equation (2). Ha / T=0.31, satisfying equation (3). Wa / T=0.78, satisfying equation (4). Ha / Hb=1.67, satisfying equation (5). It is clear that the above numerical values ​​satisfy equations (6) to (9).

[0132] Therefore, in Figure 8 In the first diffraction structure region 61A, the first diffraction structure 611 can have a diffraction efficiency characteristic that satisfies the relationship Ea1>Ea2. The second diffraction structure 612 can have a diffraction efficiency characteristic that satisfies the relationship Eb1≥Eb2. The third diffraction structure 613 can have a diffraction efficiency characteristic that satisfies the relationship Ec1<Ec2. Therefore, Figure 8 The light guide member 4A can improve the utilization efficiency of the image light L1 from the display element 2 .

[0133] [2.2 Modification 2]

[0134] Fig. 9 4B is a partial cross-sectional view of the light guide member 4B in the modification 2. In more detail, Fig. 9 It is a cross-sectional view of a portion including the first diffractive structure region 61B of the transfer region 6B in the light guide member 4B.

[0135] Fig. 9 The first diffraction structure region 61B and Figure 3 Similarly, the first diffraction structure region 61 includes a first diffraction structure 611 , a second diffraction structure 612 , and a third diffraction structure 613 . Fig. 9 The shape and size of the concavo-convex portion of the first diffractive structure region 61B, that is, the shape and size of the concavo-convex portion 611a of the first diffractive structure 611, the concavo-convex portion 612a of the second diffractive structure 612, and the concavo-convex portion 613a of the third diffractive structure 613 are the same as Figure 3The first diffraction structure region 61 and Figure 8 The first diffraction structure region 61A is different.

[0136] In this modified example, T=320 nm, Ha=180 nm, Wa=280 nm, Hb=80 nm, Wb=180 nm, Hc=150 nm, and Wc=180 nm.

[0137] Ha>Hb, satisfying equation (1). Wa>Wb, satisfying equation (2). Ha / T=0.56, satisfying equation (3). Wa / T=0.88, satisfying equation (4). Ha / Hb=2.25, satisfying equation (5). On the other hand, grating heights Ha and Hc do not satisfy equation (6), but grating heights Hb and Hc satisfy equation (7). Grating widths Wa and Wc satisfy equation (8), but grating widths Wb and Wc do not satisfy equation (9).

[0138] pass Fig. 9 The first diffraction structure region 61B satisfies the above formulas (1) to (5), so that the first diffraction structure 611 can have a diffraction efficiency characteristic that satisfies the relationship Ea1>Ea2. The second diffraction structure 612 can have a diffraction efficiency characteristic that satisfies the relationship Eb1≥Eb2. Therefore, Fig. 9 The light guide member 4B can improve the utilization efficiency of the image light L1 from the display element 2 .

[0139] In this modification, the grating heights Ha, Hb, and Hc do not satisfy the relationship of Ha<Hc, but satisfy the relationship of Hb<Hc. Here, the grating heights Ha, Hb, and Hc may also satisfy at least one of the relationship of Ha<Hc and the relationship of Hb<Hc, but preferably satisfy both the relationship of Ha<Hc and the relationship of Hb<Hc. This structure can further improve the utilization efficiency of the image light L1 from the display element 2.

[0140] In this modification, the grating widths Wa, Wb, and Wc satisfy the relationship of Wc<Wa, but do not satisfy the relationship of Wc<Wb. Here, the grating widths Wa, Wb, and Wc may also satisfy at least one of the relationship of Wc<Wa and the relationship of Wc<Wb, but preferably satisfy both the relationship of Wc<Wa and the relationship of Wc<Wb. This structure can further improve the utilization efficiency of the image light L1 from the display element 2.

[0141] [2.3 Modification 3]

[0142] Fig.10 4C is a partial cross-sectional view of the light guide member 4C in the modification 3. In more detail, Fig. 9 It is a cross-sectional view of a portion including the first diffractive structure region 61C of the transfer region 6C in the light guide member 4C.

[0143] Fig.10 The first diffraction structure region 61C and Figure 3 Similarly, the first diffraction structure region 61 includes a first diffraction structure 611 , a second diffraction structure 612 , and a third diffraction structure 613 .

[0144] exist Fig.10 In the first diffractive structure region 61C, the concavoconvex portions 611a in the first diffractive structure 611 do not have a shape in which the distance between the concavoconvex portions 611a in the periodic direction increases from the inside to the outside of the main body 40 in the thickness direction T1 of the main body 40, and the distance between the concavoconvex portions 611a in the periodic direction is constant. That is, the base end side ( Fig.10 The distance G11 between the concave-convex portion 611a located at the lower end side of the concave-convex portion 611a ( Fig.10 The distance G12 between the concave and convex parts 611a (on the upper end side) is equal.

[0145] exist Fig.10 In the first diffractive structure region 61C, the concavoconvex portions 612a in the second diffractive structure 612 do not have a shape in which the distance between the concavoconvex portions 612a in the periodic direction increases from the inside to the outside of the main body 40 in the thickness direction T1 of the main body 40, and the distance between the concavoconvex portions 612a in the periodic direction is constant. That is, the base end side ( Fig.10 The distance G21 between the concave-convex portion 612a located at the lower end side of the concave-convex portion 612a ( Fig.10 The distance G22 between the concave and convex parts 612a (on the upper end side) is equal.

[0146] exist Fig.10 In the first diffractive structure region 61C, the concavoconvex portions 613a in the third diffractive structure 613 do not have a shape in which the distance between the concavoconvex portions 613a in the periodic direction increases from the inside to the outside of the main body 40 in the thickness direction T1 of the main body 40, and the distance between the concavoconvex portions 613a in the periodic direction is constant. That is, the base end side ( Fig.10 The distance G31 between the concave-convex portion 613a located at the lower end side of the concave-convex portion 613a ( Fig.10 The distance G32 between the concave and convex parts 613a (on the upper end side) is equal.

[0147] In this modification, as an example, T = 320nm, Ha = 200nm, Wa = 300nm, Hb = 100nm, Wb = 160nm, Hc = 250nm, Wc = 180nm. That is, Ha>Hb, satisfying mathematical formula (1). Wa>Wb, satisfying mathematical formula (2). Ha / T = 0.625, satisfying mathematical formula (3). Wa / T = 0.9375, satisfying mathematical formula (4). Ha / Hb = 2, satisfying mathematical formula (5). It is clear that the above numerical values ​​satisfy mathematical formulas (6) to (9).

[0148] Therefore, in Fig.10 In the first diffraction structure region 61C, the first diffraction structure 611 can have a diffraction efficiency characteristic that satisfies the relationship Ea1>Ea2. The second diffraction structure 612 can have a diffraction efficiency characteristic that satisfies the relationship Eb1≥Eb2. The third diffraction structure 613 can have a diffraction efficiency characteristic that satisfies the relationship Ec1<Ec2. Therefore, Fig.10 The light guide member 4C can improve the utilization efficiency of the image light L1 from the display element 2.

[0149] According to this variation, the concavoconvex portions 611a in the first diffraction structure 611 may not necessarily have the following shape: the distance between the concavoconvex portions 611a in the periodic direction increases from the inside to the outside of the main body 40 in the thickness direction T1 of the main body 40.

[0150] According to this variation, the concave-convex portions 612a in the second diffraction structure 612 may not necessarily have the following shape: the distance between the concave-convex portions 612a in the periodic direction increases from the inside to the outside of the main body 40 in the thickness direction T1 of the main body 40.

[0151] According to this variation, the concave-convex portions 613a in the third diffraction structure 613 may not necessarily have the following shape: the distance between the concave-convex portions 613a in the periodic direction increases from the inside to the outside of the main body 40 in the thickness direction T1 of the main body 40.

[0152] [2.4 Modification 4]

[0153] Fig.11 4D is a partial cross-sectional view of the light guide member 4D in the modification 4. In more detail, Fig.11 It is a cross-sectional view of a portion of the light guide member 4D including the first diffractive structure region 61D of the transfer region 6D.

[0154] Fig.11 The first diffraction structure region 61D and Figure 3 Similarly, the first diffraction structure region 61 includes a first diffraction structure 611 , a second diffraction structure 612 , and a third diffraction structure 613 .

[0155] exist Fig.11 In the first diffractive structure region 61D, the central axis C1 of the concavo-convex portion 611 a in the first diffractive structure 611 is parallel to the thickness direction T1 of the main body 40 without being inclined.

[0156] exist Fig.11 In the first diffractive structure region 61D, the central axis C2 of the concavo-convex portion 612 a in the second diffractive structure 612 is parallel to the thickness direction T1 of the main body 40 without being inclined.

[0157] exist Fig.11 In the first diffractive structure region 61D, the central axis C3 of the concavo-convex portion 613 a in the third diffractive structure 613 is parallel to the thickness direction T1 of the main body 40 without being inclined.

[0158] In this modification, as an example, T = 320nm, Ha = 200nm, Wa = 300nm, Hb = 100nm, Wb = 160nm, Hc = 250nm, Wc = 180nm. That is, Ha>Hb, satisfying mathematical formula (1). Wa>Wb, satisfying mathematical formula (2). Ha / T = 0.625, satisfying mathematical formula (3). Wa / T = 0.9375, satisfying mathematical formula (4). Ha / Hb = 2, satisfying mathematical formula (5). It is clear that the above numerical values ​​satisfy mathematical formulas (6) to (9).

[0159] Therefore, in Fig.11 In the first diffraction structure region 61D, the first diffraction structure 611 can have a diffraction efficiency characteristic that satisfies the relationship Ea1>Ea2. The second diffraction structure 612 can have a diffraction efficiency characteristic that satisfies the relationship Eb1≥Eb2. The third diffraction structure 613 can have a diffraction efficiency characteristic that satisfies the relationship Ec1<Ec2. Therefore, Fig.11 The light guide member 4D can improve the utilization efficiency of the image light L1 from the display element 2 .

[0160] According to this modification, the central axis C1 of the concavo-convex portion 611 a in the first diffractive structure 611 may not necessarily be inclined with respect to the thickness direction T1 of the main body 40 .

[0161] According to this modification, the central axis C2 of the concavo-convex portion 612 a in the second diffractive structure 612 may not necessarily be inclined with respect to the thickness direction T1 of the main body 40 .

[0162] According to this modification, the central axis C3 of the concavo-convex portion 613 a in the third diffractive structure 613 may not necessarily be inclined with respect to the thickness direction T1 of the main body 40 .

[0163] [2.5 Modification 5]

[0164] Fig.12 FIG. 4 is a top view of the light guide member 4E in the modification example 5. Fig.12 As shown, the coupling region 5 and the replica region 6E are formed on the first surface 40 a of the main body 40 of the light guide member 4 .

[0165] Fig.12 The replication region 6E includes a first diffraction structure region 61E and a second diffraction structure region 62E.

[0166] The first diffraction structure area 61E is configured to be parallel to the coupling area 5 in the first direction D1. The first diffraction structure area 61E is a surface relief type diffraction grating, which periodically forms concavoconvexities. The first diffraction structure area 61E is a reflective diffraction grating. The first diffraction structure area 61E is configured to divide the image light L1 propagating in the first propagation direction intersecting the thickness direction of the main body 40 into a plurality of image lights L2 propagating in the second propagation direction intersecting the first propagation direction. In the first diffraction structure area 61E, the first direction D1 is the first propagation direction, and the second direction D2 is the second propagation direction. The first diffraction structure area 61E divides the image light L1 propagating in the main body 40 of the light guide member 4, thereby directing the plurality of image lights L2 arranged in the first direction D1 toward the second diffraction structure area 62E. In this way, the first diffraction structure area 61E expands the pupil of the image light in the first direction D1.

[0167] The first diffraction structure region 61E, like the first diffraction structure region 61, is composed of convex and concave portions in the thickness direction relative to the main body 40, and the convex and concave portions are arranged to have periodicity in the periodic direction. However, unlike the first diffraction structure region 61, it does not have a diffraction structure that is different depending on the location such as the first to third diffraction structures 611 to 613.

[0168] Fig.12The second diffraction structure area 62E is configured to be parallel to the first diffraction structure area 61E in the second direction D2. The second diffraction structure area 62E is a surface relief type diffraction grating that periodically forms concave and convex. The second diffraction structure area 62E is a transmission type diffraction grating. The second diffraction structure area 62E is configured to divide the image light L2 propagating in the first propagation direction intersecting the thickness direction of the main body 40 in the first propagation direction into a plurality of image lights L3 propagating in the second propagation direction intersecting the first propagation direction. In the second diffraction structure area 62, the second direction D2 is the first propagation direction, and the third direction D3 is the second propagation direction. The second diffraction structure area 62E divides the image light L2 propagating in the main body 40 of the light guide member 4E, thereby directing the plurality of image lights L3 arranged in the second direction D2 toward the field of view area 8. In this way, the second diffraction structure area 62E expands the pupil of the image light in the second direction D2.

[0169] Fig.12 The second diffraction structure region 62E includes a first diffraction structure 621, a second diffraction structure 622, and a third diffraction structure 623. The second diffraction structure 622 is located on the opposite side of the coupling region 5 relative to the first diffraction structure 621 in the first propagation direction (second direction D2). The third diffraction structure 623 is located on the opposite side of the first diffraction structure 621 relative to the second diffraction structure 622 in the first propagation direction (second direction D2). In other words, the first diffraction structure 621, the second diffraction structure 622, and the third diffraction structure 623 are arranged in this order in the first propagation direction (second direction D2).

[0170] like Fig.12As shown, the second diffraction structure region 62E has a first end 62a on the coupling region 5 side in the first propagation direction (second direction D2), and a second end 62b on the side opposite to the coupling region 5 in the first propagation direction (second direction D2). The first diffraction structure 621 is located at least in a region R21 that occupies 1 / 4 of the second diffraction structure region 62E from the first end 62a of the second diffraction structure region 62E in the first propagation direction. The second diffraction structure 622 is located at least in a region R22 that occupies 1 / 2 of the second diffraction structure region 62E from the first end 62a of the second diffraction structure region 62E in the first propagation direction. The third diffraction structure 623 is located at least in the first propagation direction relative to the second diffraction structure 622 on the side opposite to the first diffraction structure 621, and is located in a region R23 that occupies 1 / 4 of the second diffraction structure region 62E from the second end 62b of the second diffraction structure region 62E in the first propagation direction. As an example, in the second diffraction structure region 62E, the region R21 may be occupied by the first diffraction structure 621 , the region R23 may be occupied by the third diffraction structure 623 , and the area between the region R21 and the region R23 may be occupied by the second diffraction structure 622 .

[0171] The second diffraction structure region 62E is composed of concavoconvex parts in the thickness direction relative to the main body 40, and the concavoconvex parts are arranged to have periodicity in the periodic direction, that is, the concavoconvex parts of the first diffraction structure 621, the concavoconvex parts of the second diffraction structure 622, and the concavoconvex parts of the third diffraction structure 623. The concavoconvex parts are convex parts protruding from the main body 40. The periodic direction is the direction in which the concavoconvex parts are arranged to have periodicity. The periodic direction includes the component of the first propagation direction (the second direction D2 in the case of the second diffraction structure region 62E). In order to convert the image light L2 propagating in the second direction D2 into the image light L3 propagating in the third direction D3, the periodic direction is set to the second direction D2. In this case, the periodic direction only includes the component of the second direction D2. The periodic direction is the direction of the wave number vector of the second diffraction structure region 62. The concavoconvex parts extend in the first direction D1, for example, and are arranged at a given interval in the second direction D2. The grating period is constant in the second diffractive structure region 62. That is, the first diffractive structure 621, the second diffractive structure 622, and the third diffractive structure 623 have the same grating period. The grating period is the distance between the same positions of two adjacent concavoconvex portions in the period direction.

[0172] The first diffraction structure 621, the second diffraction structure 622, and the third diffraction structure 623 of the second diffraction structure region 62E have the same grating period, but have different diffraction efficiency characteristics because at least one of the grating height and the grating width is different. The grating height and grating width of the first diffraction structure 621, the second diffraction structure 622, and the third diffraction structure 623 of the second diffraction structure region 62E can be set in the same manner as the grating height and grating width of the first diffraction structure 621, the second diffraction structure 622, and the third diffraction structure 623 of the first diffraction structure region 61 in the above-mentioned embodiment.

[0173] That is, when the grating period of the second diffraction structure region 62E is set to T, and the grating height (the height of the concavoconvex portion) of the first diffraction structure 621 is set to Ha, the grating period T and the grating height Ha satisfy the relationship of 0.3<Ha / T<1.2. When the grating width (the width of the concavoconvex portion) of the first diffraction structure 621 is set to Wa, the grating period T and the grating width Wa satisfy the relationship of 0.7<Wa / T<1.0. When the grating height (the height of the concavoconvex portion) of the second diffraction structure 622 is set to Hb, the grating height Ha and the grating height Hb satisfy the relationship of 1.2<Ha / Hb<10.0. Thus, in the first diffraction structure 621, the diffraction efficiency of the light whose incident angle (propagation angle) with respect to the interface of the main body 40 is the largest among the light propagating in the second direction D2 is set to Ea1, and the diffraction efficiency of the light whose incident angle (propagation angle) with respect to the interface of the main body 40 is the smallest among the light propagating in the second direction D2 is set to Ea2, and the first diffraction structure 621 has a diffraction efficiency characteristic satisfying the relationship of Ea1>Ea2. In the second diffraction structure 622, the diffraction efficiency of the light whose incident angle (propagation angle) with respect to the interface of the main body 40 is the largest among the light propagating in the second direction D2 is set to Eb1, and the diffraction efficiency of the light whose incident angle (propagation angle) with respect to the interface of the main body 40 is the smallest among the light propagating in the second direction D2 is set to Eb2, and the second diffraction structure 622 has a diffraction efficiency characteristic satisfying the relationship of Eb1≥Eb2. In this modified example, Eb1=Eb2.

[0174] When the grating height of the third diffraction structure 623 is set to Hc, the grating heights Ha, Hb, and Hc satisfy the relationship of Ha<Hc and the relationship of Hb<Hc. When the grating width of the third diffraction structure 623 is set to Wc, the grating widths Wa, Wb, and Wc satisfy the relationship of Wc<Wa and the relationship of Wc<Wb. Thus, in the third diffraction structure 623, the diffraction efficiency of the light whose incident angle (propagation angle) relative to the interface of the main body 40 is the largest among the light propagating along the second direction D2 is set to Ec1, and the diffraction efficiency of the light whose incident angle (propagation angle) relative to the interface of the main body 40 is the smallest among the light propagating along the second direction D2 is set to Ec2, and the third diffraction structure 623 has a diffraction efficiency characteristic that satisfies the relationship of Ec1<Ec2.

[0175] In the second diffraction structure region 62E described above, the first diffraction structure 621 has a diffraction efficiency characteristic that satisfies the relationship of Ea1>Ea2. Therefore, the first diffraction structure 621 can reduce the amount of emitted light that does not reach the field of view region 8 in the second direction D2. Therefore, the utilization efficiency of the image light L1 from the display element 2 can be improved. On the other hand, the first diffraction structure 621 can increase the amount of emitted light that reaches the field of view region 8 in the second direction D2. Therefore, the utilization efficiency of the image light L1 from the display element 2 can be improved. The second diffraction structure 622 has a diffraction efficiency characteristic that satisfies the relationship of Eb1=Eb2. Therefore, the second diffraction structure 612 can reduce the deviation of the light amount of the emitted light L11b, L12b, and L13b in the second direction D2. The third diffraction structure 623 has a diffraction efficiency characteristic that satisfies the relationship of Ec1<Ec2. As a result, the amount of emitted light that reaches the field of view region 8 in the second direction D2 can be increased. Therefore, it is possible to improve the utilization efficiency of the image light L1 from the display element 2. Therefore, the second diffractive structure region 62E can improve the utilization efficiency of the image light L1 from the display element 2.

[0176] [2.6 Other Modifications]

[0177] In a modified example, the light guide members 4 to 4E do not necessarily need to be arranged so that the light guide members 4 to 4E and the viewing area 8 are arranged in a straight line. In other words, the optical path from the light guide members 4 to 4E to the viewing area 8 is not necessarily a straight line. For example, the light from the light guide members 4 to 4E may be reflected by a reflector, a combiner, a windshield, etc., and made incident on the viewing area 8. In this case, the optical path from the light guide members 4 to 4E to the viewing area 8 is not a straight line, and is, for example, an L-shaped.

[0178] In a modified example, the shape and size of the light guide members 4 to 4E are set so that the user can visually recognize the virtual image even if the length of the optical path from the light guide members 4 to 4E to the visual field area 8 is 300 mm or more. As an example, the size of the visual field area 8 corresponding to the first propagation direction (first direction D1) of the copy area 6 is set to V1, and the size of the first propagation direction (first direction D1) of the copy area 6 is set to E1, and the relationship of 1.0<E1 / V1<5.0 is satisfied. This structure can also use the optical system 3 for a head-up display (HUD) or the like in which the distance between the user and the optical system 3 is relatively far compared to the HMD.

[0179] In a modified example, the coupling region 5 is not limited to the surface relief type diffraction grating, and may include a volume hologram element (holographic diffraction grating) or a half mirror.

[0180] In a modified example, the replication area 6 may be a surface relief diffraction grating of either a transmission type or a reflection type.

[0181] In a modified example, the surface relief type diffraction grating is not limited to being formed of the same material as the light guide components 4 to 4E, but may be formed of different materials. For example, the material of the light guide components 4 to 4E may be glass, and the material of the surface relief type diffraction grating may be an ultraviolet curing resin. In this case, the surface relief type diffraction grating can be formed by nanoimprinting technology. In this way, the coupling region 5 or the replication region 6 does not necessarily need to be formed integrally with the main body 40, and may be formed separately from the main body 40.

[0182] In a modified example, the replication region 6 may include any one of the first diffraction structure regions 61 to 61D and the second diffraction structure region 62E. Thus, the replication region 6 can reduce the amount of emitted light that does not reach the viewing area 8 in both the first direction D1 and the second direction D2, thereby improving the utilization efficiency of the image light L1 from the display element 2.

[0183] In a modified example, the replication areas 6 to 6E may not have both the first diffraction structure area 61 and the second diffraction structure area 62. In this case, the replication areas 6 to 6E expand the pupil of the image light L1 in only one direction. For example, the first diffraction structure areas 61 to 61E may also be configured such that the second propagation direction D2 is a direction from the main body 40 toward the field of view area 8. In other words, the first diffraction structure areas 61 to 61E may also define an emission structure that causes the image light L1 incident on the main body 40 to be emitted from the main body 40 toward the field of view area 8 through the coupling area 5.

[0184] In a modified example, the concavoconvex parts of the first diffraction structure regions 61 to 61E can be any of protrusions (convex parts), concave parts, or a combination of convex parts and concave parts as long as they can form a diffraction grating. The central axis of the concavoconvex part can be, for example, the central axis of the protrusion or the central axis of the concave part. This is also the case in the second diffraction structure regions 62 and 62E.

[0185] In a modified example, the projection optical system 7 is not a single optical element, but may be a plurality of optical elements including a first optical element and a second optical element. The first optical element is, for example, a cemented lens in which a negative meniscus lens and a biconvex lens are combined, and the second optical element is a cemented lens in which a positive meniscus lens and a negative meniscus lens are combined. In addition, the optical system 3 may not include the projection optical system 7.

[0186] In a modified example, the projection optical system 7 and the coupling region 5 do not necessarily need to be arranged in a straight line. That is, the optical path of the image light L1 from the projection optical system 7 to the coupling region 5 is not necessarily a straight line. For example, the image light L1 from the projection optical system 7 may be reflected by a reflector and made incident on the coupling region 5. In this case, the optical path of the image light L1 from the projection optical system 7 to the coupling region 5 is not a straight line, for example, an L-shape.

[0187] In a modified example, the image display device 1 may include a plurality of light guide members 4 to 4E corresponding to the wavelengths of light included in the image light L1 , respectively. This makes it possible to provide a color image to the user.

[0188] [3. Method]

[0189] As is clear from the above-mentioned embodiment and modification examples, the present disclosure includes the following aspects. In order to clearly indicate the correspondence with the embodiment, bracketed symbols are given below.

[0190] The first mode is an optical system (3), which comprises: a light guiding member (4; 4A; 4B; 4C; 4D; 4E) that guides image light (L1) forming an image output from a display element (2) as a virtual image to a user's field of view (8). The light-guiding member (4; 4A; 4B; 4C; 4D; 4E) comprises: a plate-shaped main body (40); a coupling region (5) formed in the main body (40) and causing the image light (L1) to be incident into the main body (40) so that the image light (L1) propagates in the main body (40); and a copy region (6; 6A; 6B; 6C; 6D; 6E) formed in the main body (40) and having a diffraction structure region (61) as a surface relief type diffraction grating, wherein the diffraction structure region (61) divides the image light (L1) propagating in a first propagation direction (D1) intersecting with a thickness direction (T1) of the main body (40) into a plurality of image lights (L2) propagating in a second propagation direction (D2) intersecting with the first propagation direction (D1). The diffraction structure region (61) includes a first diffraction structure (611) and a second diffraction structure (612) located on the side opposite to the coupling region (5) relative to the first diffraction structure (611) in the first propagation direction (D1). The grating height of the first diffraction structure (611) is higher than the grating height of the second diffraction structure (612). The grating width of the first diffraction structure (611) is wider than the grating width of the second diffraction structure (612). This method can improve the utilization efficiency of the image light (L1) from the display element (2).

[0191] The second mode is an optical system (3) based on the first mode. In the second mode, the diffraction structure region (61) satisfies the following relationship: 0.3<Ha / T<1.2, 0.7<Wa / T<1.0, 1.2<Ha / Hb<10.0. T is the grating period of the diffraction structure region (61), Ha is the grating height of the first diffraction structure (611), Wa is the grating width of the first diffraction structure (611), and Hb is the grating height of the second diffraction structure (612). This mode can improve the utilization efficiency of the image light (L1) from the display element (2).

[0192] The third mode is an optical system (3) based on the first or second mode. In the third mode, the first diffraction structure (611) has the following diffraction efficiency characteristics: the diffraction efficiency of light (L12) whose incident angle with respect to the interface of the main body (40) is the largest among the light propagating along the first propagation direction (D1) is greater than the diffraction efficiency of light (L13) whose incident angle with respect to the interface of the main body (40) is the smallest among the light propagating along the first propagation direction (D1). This mode can further improve the utilization efficiency of the image light (L1) from the display element (2).

[0193] The fourth aspect is an optical system (3) based on the third aspect. In the fourth aspect, the second diffraction structure (612) has the following diffraction efficiency characteristics: the diffraction efficiency of light (L12) whose incident angle with respect to the interface of the main body (40) is the largest among the light propagating along the first propagation direction (D1) is greater than the diffraction efficiency of light (L13) whose incident angle with respect to the interface of the main body (40) is the smallest among the light propagating along the first propagation direction (D1). This aspect can further improve the utilization efficiency of the image light (L1) from the display element (2).

[0194] The fifth mode is an optical system (3) based on any one of the first to fourth modes. In the fifth mode, the diffraction structure region (61) further includes a third diffraction structure (613). The third diffraction structure (613) is located on the opposite side of the first diffraction structure (611) relative to the second diffraction structure (612) in the first propagation direction (D1). The diffraction structure region (61) satisfies at least one of the relationship Ha<Hc and the relationship Hb<Hc. Hc is the grating height of the third diffraction structure (613). This mode can further improve the utilization efficiency of the image light (L1) from the display element (2).

[0195] In the fifth aspect, the diffractive structure region (61) may satisfy both the relationship of Ha<Hc and the relationship of Hb<Hc. In this case, the utilization efficiency of the image light (L1) from the display element (2) can be further improved.

[0196] The sixth mode is an optical system (3) based on the fifth mode. In the sixth mode, the diffraction structure region (61) satisfies at least one of the relationship of Wc<Wa and the relationship of Wc<Wb. Wa is the grating width of the first diffraction structure (611). Wb is the grating width of the second diffraction structure (612). Wc is the grating width of the third diffraction structure (613). This mode can further improve the utilization efficiency of the image light (L1) from the display element (2).

[0197] In the sixth aspect, the diffractive structure region (61) may satisfy both the relationship of Wc<Wa and the relationship of Wc<Wb. In this case, the utilization efficiency of the image light (L1) from the display element (2) can be further improved.

[0198] The seventh aspect is an optical system (3) based on the fifth or sixth aspect. In the seventh aspect, the third diffraction structure (613) has the following diffraction efficiency characteristics: the diffraction efficiency of light (L12) whose incident angle with respect to the interface of the main body (40) is the largest among the light propagating along the first propagation direction (D1) is smaller than the diffraction efficiency of light (L13) whose incident angle with respect to the interface of the main body (40) is the smallest among the light propagating along the first propagation direction (D1). This aspect can further improve the utilization efficiency of the image light (L1) from the display element (2).

[0199] The eighth mode is an optical system (3) based on any one of the first to seventh modes. In the eighth mode, the diffraction structure region (61) is composed of concave-convex portions (611a, 612a, 613a) relative to the thickness direction (T1) of the main body (40), and the concave-convex portions (611a, 612a, 613a) are arranged to have periodicity in the periodic direction of the component including the first propagation direction (D1). The central axis (C1) of the concave-convex portion (611a) in the first diffraction structure (611) is inclined relative to the thickness direction (T1) of the main body (40). This mode can further improve the utilization efficiency of the image light (L1) from the display element (2).

[0200] The ninth aspect is an optical system (3) based on the eighth aspect. In the ninth aspect, the concavoconvex portion (611a) in the first diffractive structure (611) has a shape such that, in the thickness direction (T1) of the main body (40), the distance between the concavoconvex portions (611a) in the periodic direction increases from the inside to the outside of the main body (40). This aspect can facilitate the manufacture of the light guide member (4).

[0201] The tenth mode is an optical system (3) based on the eighth or ninth mode. In the tenth mode, the central axis (C2) of the concavoconvex portion (612a) in the second diffractive structure (612) is inclined relative to the thickness direction (T1) of the main body (40). This mode can further improve the utilization efficiency of the image light (L1) from the display element (2).

[0202] The 11th mode is an optical system (3) based on the 10th mode. In the 11th mode, the inclination angle of the central axis (C1) of the concavoconvex portion (611a) in the first diffractive structure (611) relative to the thickness direction (T1) of the main body (40) is set to θa, and the inclination angle of the central axis (C2) of the concavoconvex portion (612a) in the second diffractive structure (612) relative to the thickness direction (T1) of the main body (40) is set to θb, and the relationship of 0.9<θa / θb<1.1 is satisfied. This mode can further improve the utilization efficiency of the image light (L1) from the display element (2).

[0203] The twelfth method is an optical system (3) based on any one of the eighth to eleventh methods. In the twelfth method, the diffraction structure region (61) further includes a third diffraction structure (613). The third diffraction structure (613) is located on the opposite side of the first diffraction structure (611) relative to the second diffraction structure (612) in the first propagation direction (D1). The diffraction structure region (61) satisfies at least one of the relationship Ha<Hc and the relationship Hb<Hc. Hc is the grating height of the third diffraction structure (613). The central axis (C3) of the concave-convex portion (613a) in the third diffraction structure (613) is inclined relative to the thickness direction (T1) of the main body (40). This method can further improve the utilization efficiency of the image light (L1) from the display element (2).

[0204] In the twelfth embodiment, the diffraction structure region (61) can satisfy at least one of the relationship of Wc<Wa and the relationship of Wc<Wb. Wa is the grating width of the first diffraction structure (611). Wb is the grating width of the second diffraction structure (612). Wc is the grating width of the third diffraction structure (613). This embodiment can further improve the utilization efficiency of the image light (L1) from the display element (2).

[0205] The 13th mode is an optical system (3) based on the 12th mode. In the 13th mode, the inclination angle of the central axis (C1) of the concavoconvex portion (611a) in the first diffractive structure (611) relative to the thickness direction (T1) of the main body (40) is set to θa, and the inclination angle of the central axis (C3) of the concavoconvex portion (613a) in the third diffractive structure (613) relative to the thickness direction (T1) of the main body (40) is set to θc, and the relationship of 0.9<θa / θc<1.1 is satisfied. This mode can further improve the utilization efficiency of the image light (L1) from the display element (2).

[0206] A 14th aspect is an optical system (3) according to any one of the 1st to 13th aspects. In the 14th aspect, the copy area (6; 6A; 6B; 6C; 6D; 6E) has an emission structure (62), and the emission structure (62) causes the image light (L1) incident on the main body (40) to be emitted from the main body (40) toward the field of view area (8) through the coupling area (5). This aspect does not require the emission structure to be provided independently of the copy area (6; 6A; 6B; 6C; 6D; 6E), so that the light guide member (4) can be miniaturized.

[0207] The fifteenth aspect is an optical system (3) according to any one of the first to fourteenth aspects. In the fifteenth aspect, the size of the field of view area (8) corresponding to the first propagation direction (D1) of the copy area (6; 6A; 6B; 6C; 6D; 6E) is set to V1, and the size of the first propagation direction (D1) of the copy area (6; 6A; 6B; 6C; 6D; 6E) is set to E1, and the relationship of 1.0<E1 / V1<5.0 is satisfied. This aspect can also use the optical system (3) for HUDs and the like in which the distance between the user and the optical system (3) is relatively far compared to HMDs.

[0208] The 16th mode is an optical system (3) based on any one of the 1st to 15th modes. In the 16th mode, the diffraction structure region (61) has a first end (61a) on the coupling region (5) side in the first propagation direction (D1), and a second end (61b) on the side opposite to the coupling region (5) in the first propagation direction (D1). The first diffraction structure (611) is located in a region (R11) that occupies 1 / 4 of the diffraction structure region (61, 62) from the first end (61a) of the diffraction structure region (61, 62) in the first propagation direction (D1). This mode can further improve the utilization efficiency of the image light (L1) from the display element (2).

[0209] The 17th mode is an optical system (3) based on the 16th mode. In the 17th mode, the second diffractive structure (612) is located in a region (R12) occupying 1 / 2 of the diffractive structure region (61) from the first end (61a) of the diffractive structure region (61) in the first propagation direction (D1). This mode can further improve the utilization efficiency of the image light (L1) from the display element (2).

[0210] The 18th aspect is an optical system (3) based on the 16th or 17th aspect. In the 18th aspect, the diffraction structure region (61) further includes a third diffraction structure (613). The third diffraction structure (613) is located on the opposite side of the first diffraction structure (611) relative to the second diffraction structure (612) in the first propagation direction (D1), and is located in a region (R13) occupying 1 / 4 of the diffraction structure region (61) from the second end (61b) of the diffraction structure region (61) in the first propagation direction (D1). The diffraction structure region (61) satisfies at least one of the relationship Ha<Hc and the relationship Hb<Hc. Ha is the grating height of the first diffraction structure (611). Hb is the grating height of the second diffraction structure (612). Hc is the grating height of the third diffraction structure (613). This method can further improve the utilization efficiency of the image light (L1) from the display element (2).

[0211] A 19th aspect is an optical system (3) according to any one of the 1st to 18th aspects. In the 19th aspect, the optical system (3) further comprises: a projection optical system (7) for causing the image light (L1) to enter the coupling region (5) of the light guide member (4; 4A; 4B; 4C; 4D; 4E) as substantially collimated light. This aspect can further improve the utilization efficiency of the image light (L1) from the display element (2).

[0212] A 20th aspect is an image display device (1) comprising an optical system (3) according to any one of the first to nineteenth aspects and the display element (2). This aspect can improve the utilization efficiency of image light (L1) from the display element (2).

[0213] The above-mentioned methods 2 to 19 are not essential.

[0214] As described above, as an illustration of the technology disclosed in the present invention, an embodiment is described. For this purpose, drawings and detailed descriptions are provided. Therefore, among the structural elements recorded in the drawings and detailed descriptions, not only the structural elements necessary for solving the problem can be included, but also the structural elements that are not necessary for solving the problem can be included in order to illustrate the above-mentioned technology. Therefore, it should not be immediately determined that these non-essential structural elements are necessary based on the fact that these non-essential structural elements are recorded in the drawings and detailed descriptions. In addition, since the above-mentioned embodiments are used to illustrate the technology disclosed in the present invention, various changes, substitutions, additions, omissions, etc. can be made in the claims or their equivalents.

[0215] Industrial Applicability

[0216] The present disclosure can be applied to an optical system and an image display device. Specifically, the present disclosure can be applied to an optical system for guiding image light from a display element as a virtual image to a user's visual field, and an image display device including the optical system.

[0217] -Explanation of symbols-

[0218] 1 Image display device

[0219] 2 Display components

[0220] 3 Optical system

[0221] 4, 4A, 4B, 4C, 4D, 4E Light guide components

[0222] 40 Main body

[0223] 5 Coupling region

[0224] 6, 6A, 6B, 6C, 6D, 6E Copy area

[0225] 61 The first diffraction structure region (diffraction structure region)

[0226] 61a End 1

[0227] 61b End 2

[0228] R11, R12, R13 areas

[0229] 611 1st Diffraction Structure

[0230] 611a Concavoconvex part

[0231] 612 Second Diffraction Structure

[0232] 612a Concavoconvex part

[0233] 613 The third diffraction structure

[0234] 613a Concavoconvex part

[0235] 62 Second diffraction structure region (diffraction structure region, emission structure)

[0236] 7 Projection optical system

[0237] 8 Field of view

[0238] L1, L2 image light

[0239] D1 1st direction (1st propagation direction)

[0240] D2 Second direction (second propagation direction)

[0241] T1 thickness direction

[0242] C1, C2, C3 central axes.

Claims

1. An optical system, comprising: a light guide member that guides image light forming an image output from a display element as a virtual image to a viewing area of a user; wherein the light guide member comprises: a plate-shaped main body portion; a coupling region formed in the main body portion, through which the image light enters the main body portion so that the image light propagates within the main body portion; and a replication region formed in the main body portion, having a diffraction structure region that is a surface relief type diffraction grating, the diffraction structure region splitting, in a first propagation direction, the image light propagating in a first propagation direction intersecting the thickness direction of the main body portion into a plurality of image lights propagating in a second propagation direction intersecting the first propagation direction; the diffraction structure region includes a first diffraction structure and a second diffraction structure that is located on a side opposite to the coupling region with respect to the first diffraction structure in the first propagation direction; the grating height of the first diffraction structure is higher than the grating height of the second diffraction structure; the grating width of the first diffraction structure is wider than the grating width of the second diffraction structure.

2. The optical system according to claim 1, wherein the diffraction structure region satisfies the following relationships: 0.3 < Ha / T < 1.2, 0.7 < Wa / T < 1.0, 1.2 < Ha / Hb < 10.0, T is the grating period of the diffraction structure region; Ha is the grating height of the first diffraction structure; Wa is the grating width of the first diffraction structure; Hb is the grating height of the second diffraction structure.

3. The optical system according to claim 1 or 2, wherein the first diffraction structure has the following diffraction efficiency characteristic: the diffraction efficiency of light having the maximum incident angle with respect to the interface of the main body portion among the light propagating in the first propagation direction is greater than the diffraction efficiency of light having the minimum incident angle with respect to the interface of the main body portion among the light propagating in the first propagation direction.

4. The optical system according to claim 3, wherein the second diffraction structure has the following diffraction efficiency characteristic: the diffraction efficiency of light having the maximum incident angle with respect to the interface of the main body portion among the light propagating in the first propagation direction is greater than or equal to the diffraction efficiency of light having the minimum incident angle with respect to the interface of the main body portion among the light propagating in the first propagation direction.

5. The optical system according to any one of claims 1 to 4, wherein the diffraction structure region further includes a third diffraction structure; the third diffraction structure is located on a side opposite to the first diffraction structure with respect to the second diffraction structure in the first propagation direction; the diffraction structure region satisfies at least one of the relationships Ha < Hc and Hb < Hc; Ha is the grating height of the first diffraction structure; Hb is the grating height of the second diffraction structure; Hc is the grating height of the third diffraction structure.

6. The optical system according to claim 5, wherein the diffraction structure region satisfies at least one of the relationships Wc < Wa and Wc < Wb; Wa is the grating width of the first diffraction structure; Wb is the grating width of the second diffraction structure, Wc is the grating width of the third diffraction structure.

7. The optical system according to claim 5 or 6, wherein, the third diffraction structure has the following diffraction efficiency characteristics: the diffraction efficiency of the light that travels along the first propagation direction and has the maximum incident angle with respect to the interface of the main body portion is smaller than the diffraction efficiency of the light that travels along the first propagation direction and has the minimum incident angle with respect to the interface of the main body portion.

8. The optical system according to any one of claims 1 to 7, wherein, the diffraction structure region is composed of concavo-convex portions in the thickness direction of the main body portion, and the concavo-convex portions are arranged to be periodic in the periodic direction including the component of the first propagation direction, the central axis of the concavo-convex portions in the first diffraction structure is inclined with respect to the thickness direction of the main body portion.

9. The optical system according to claim 8, wherein, the concavo-convex portions in the first diffraction structure have the following shape: in the thickness direction of the main body portion, as going from the inside to the outside of the main body portion, the distance between the concavo-convex portions in the periodic direction becomes larger.

10. The optical system according to claim 8 or 9, wherein, the central axis of the concavo-convex portions in the second diffraction structure is inclined with respect to the thickness direction of the main body portion.

11. The optical system according to claim 10, wherein, assuming the inclination angle of the central axis of the concavo-convex portions in the first diffraction structure with respect to the thickness direction of the main body portion is θa, and the inclination angle of the central axis of the concavo-convex portions in the second diffraction structure with respect to the thickness direction of the main body portion is θb, then the relationship 0.9 < θa / θb < 1.1 is satisfied.

12. The optical system according to any one of claims 8 to 11, wherein, the diffraction structure region further includes a third diffraction structure, the third diffraction structure is located on the side opposite to the first diffraction structure with respect to the second diffraction structure in the first propagation direction, the diffraction structure region satisfies at least one of the relationships Ha < Hc and Hb < Hc, Hc is the grating height of the third diffraction structure, the central axis of the concavo-convex portions in the third diffraction structure is inclined with respect to the thickness direction of the main body portion.

13. The optical system according to claim 12, wherein, assuming the inclination angle of the central axis of the concavo-convex portions in the first diffraction structure with respect to the thickness direction of the main body portion is θa, and the inclination angle of the central axis of the concavo-convex portions in the third diffraction structure with respect to the thickness direction of the main body portion is θc, then the relationship 0.9 < θa / θc < 1.1 is satisfied.

14. The optical system according to any one of claims 1 to 13, wherein, the replication region has an emission structure, and the emission structure causes the image light incident into the main body portion to be emitted from the main body portion toward the viewing region through the coupling region.

15. The optical system according to any one of claims 1 to 14, wherein, Let the size of the visual field region corresponding to the first propagation direction of the replication region be V1, and the size of the first propagation direction of the replication region be E1. Then, the relationship 1.0 < E1 / V1 < 5.0 is satisfied.

16. The optical system according to any one of claims 1 to 15, wherein the diffraction structure region has a first end on the coupling region side in the first propagation direction and a second end on a side opposite to the coupling region in the first propagation direction, the first diffraction structure is at least located in a region that occupies 1 / 4 of the diffraction structure region from the first end of the diffraction structure region in the first propagation direction.

17. The optical system according to claim 16, wherein the second diffraction structure is at least located in a region that occupies 1 / 2 of the diffraction structure region from the first end of the diffraction structure region in the first propagation direction.

18. The optical system according to claim 16 or 17, wherein the diffraction structure region further includes a third diffraction structure, the third diffraction structure is at least located on a side opposite to the first diffraction structure with respect to the second diffraction structure in the first propagation direction, and is located in a region that occupies 1 / 4 of the diffraction structure region from the second end of the diffraction structure region in the first propagation direction, the diffraction structure region satisfies at least one of the relationships Ha < Hc and Hb < Hc, Ha is the grating height of the first diffraction structure, Hb is the grating height of the second diffraction structure, Hc is the grating height of the third diffraction structure.

19. The optical system according to any one of claims 1 to 18, wherein the optical system further includes: a projection optical system that makes the image light enter the coupling region of the light guide member as substantially collimated light.

20. An image display device, comprising: the optical system according to any one of claims 1 to 19; and the display element.

Images