Optical system and image display device

Abstract

Provided are an optical system and an image display device with which it is possible to increase the pupil filling rate of image light in a field-of-view region and to reduce the size of an incident region. The optical system (3) is provided with a light guide member (5). The light guide member (5) is provided with: an incidence region (51) for causing the image light (L1) to be incident into the main body section (50); and an emission expansion region (53) having a diffraction structure that divides the image light (L1B) into a plurality of image light (L2) and emits the image light (L2) from the main body section (50). The emission expansion region (53) branches the image light (L1B) into first to third image light (L11, L12, L13). The first image light (L11) and the third image light (L13) are emitted from the emission expansion region (53) at different angles and propagate within the main body section (50). The emission expansion region (53) includes an overlapping portion (53a) where the first image light (L11) and the third image light (L13) are incident in a partially overlapping state. The optical path length difference between the first image light (L11) and the third image light (L13) incident on the overlapping portion (53a) is longer than the coherence length of the image light (L1).

Description

Technical Field

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

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

[0003] Prior Art Literature

[0004] Patent Literature

[0005] Patent Document 1: U.S. Patent No. 10429645 Summary of the invention

[0006] Problems to be solved by the invention

[0007] The optical element described in Patent Document 1 is used in, for example, image display devices such as head mounted displays. In image display devices, a decrease in the filling rate of the pupil of image light forming an image in a user's field of view is one cause of a decrease in image quality.

[0008] The present disclosure provides an optical system and an image display device capable of increasing the filling rate of a pupil of image light in a field of view and reducing the size of an incident area.

[0009] Means for solving problems

[0010] An optical system according to one embodiment of the present disclosure includes a light guide member that guides image light that forms an image output from a display element to a user's field of view as an optical image. The light guide member includes: a plate-shaped main body; an incident area formed in the main body, which allows the image light to be incident on the main body so that the image light propagates in the main body; and an exit expansion area formed in the main body, which has a diffraction structure that splits the image light propagating in a first propagation direction that intersects the thickness direction of the main body into a plurality of image lights propagating in a second propagation direction that intersects the first propagation direction, and emits the image light from the main body. The exit expansion area causes the image light propagating in the first propagation direction that is incident on the exit expansion area to branch into a first image light, a second image light, and a third image light in a given plane including the first propagation direction and the second propagation direction. The first image light is emitted from the exit expansion area at a first angle that is equal to the propagation angle of the image light propagating from the incident area to the exit expansion area in the given plane, and propagates in the main body. The second image light is emitted from the emission expansion area at a second angle different from the first angle, and is emitted from the main body. The third image light is emitted from the emission expansion area at a third angle different from the first angle and the second angle, and propagates in the main body. The emission expansion area includes an overlapping portion where the first image light and the third image light are incident in a state of partially overlapping in a given plane. The optical path length difference between the first image light and the third image light incident on the overlapping portion is longer than the coherence length of the image light.

[0011] An image display device according to one aspect of the present disclosure includes the above-mentioned optical system and a display element.

[0012] Effects of the Invention

[0013] The method of the present disclosure can improve the filling rate of the pupil of the image light in the field of view area and can reduce the size of the incident area. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a schematic diagram of a configuration example of a moving object including an image display device according to an embodiment.

[0015] Figure 2 is from Figure 1 An explanatory diagram of the optical path of image light emitted from a display element of an image display device.

[0016] Figure 3 yes Figure 1 A three-dimensional diagram of a structural example of a light guide component of an image display device.

[0017] Figure 4 yes Figure 3 A schematic top view of a light-guiding component.

[0018] Figure 5 yes Figure 3 A partial schematic cross-sectional view of a light-guiding component.

[0019] Figure 6 This is a diagram illustrating the coherence length of image light.

[0020] Figure 7 yes Figure 3 An illustration of the diffraction pattern of image light by the emission expansion area of ​​the light-guiding component.

[0021] Figure 8 yes Figure 3 An illustration of an example of diffraction of image light by an emission expansion area of ​​a light-guiding component.

[0022] Fig. 9 yes Figure 3 An illustration of an example of diffraction of image light by an emission expansion area of ​​a light-guiding component.

[0023] Fig.10 This is an explanatory diagram of an example of diffraction of image light by the light guide member of Reference Example 1.

[0024] Fig.11 This is an explanatory diagram of an example of diffraction of image light by the light guiding member of Reference Example 2.

[0025] Fig.12 This is an explanatory diagram of an example of diffraction of image light by the light-guiding component of Reference Example 3.

[0026] Fig.13 This is an explanatory diagram of an example of diffraction of image light by the light-guiding component of Reference Example 4. DETAILED DESCRIPTION

[0027] Hereinafter, the embodiments will be described in detail with appropriate reference to the drawings. However, sometimes more detailed descriptions than necessary are omitted. For example, sometimes detailed descriptions of well-known matters and repeated descriptions of substantially the same structures are 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 inventor(s) provide the drawings and the following descriptions in order to enable those skilled in the art to fully understand the present disclosure, and it is not their intention to limit the subject matter described in the claims by these.

[0028] Unless otherwise stated, 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 figures, and the size and thickness ratios of the components in the figures do not necessarily reflect the actual size ratios. In addition, the size ratios of the components are not limited to the ratios shown in the drawings.

[0029] In the present disclosure, regarding light, expressions such as "cause it to go to the 00 direction" and "cause it to propagate along the 00 direction" mean that the light forming the image as a whole goes to the 00 direction, and the light rays included in the light forming the image may also be inclined relative to the 00 direction. For example, regarding "light going to the 00 direction", as long as the main light ray of the light goes to the 00 direction, the secondary light rays of the light may also be inclined relative to the 00 direction.

[0030] [1. Implementation Method]

[0031] [1.1, Structure]

[0032] Figure 1 It is a schematic diagram of a moving object 100 including the image display device 1 according to the present embodiment. Figure 1 The moving object 100 is a car. In the following, the moving object 100 may be shown as a car 100 only to facilitate understanding. Figure 1 The image display device 1 is a head-up display (HUD: Head-Up Display) used in a car 100 .

[0033] Figure 1 The image display device 1 is disposed in a vehicle cabin of a vehicle 100 so as to project an image onto a windshield 101 of the vehicle 100 from below. Figure 1 In the embodiment, an image display device 1 is arranged in an instrument panel below a windshield 101. When an image is projected from the image display device 1 onto the windshield 101, the image reflected by the windshield 101 is visually recognized by a user D (driver, observer). The user D recognizes the image projected from the image display device 1 as a virtual image Iv. In this way, the image display device 1 displays the virtual image Iv by superimposing it on a real scene that can be visually recognized through the windshield 101.

[0034] Figure 1 The image display device 1 includes a display element 2 , an optical system 3 , and a control device 4 .

[0035] The display element 2 outputs image light L1 that forms an image in order to display an image (video). Figure 1 In the figure, for the sake of simplicity, the image light L1 is drawn as directional light with an arrow, but in fact, it is incident on the optical system 3 as light with an angle equivalent 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 the light output from the center of the display element 2 (that is, the central light ray of the image light L1).

[0036] Examples of the display element 2 include known displays such as a liquid crystal display, an organic EL display, a scanning MEMS mirror, an LCOS (Liquid Crystal On Silicon), a DMD (Digital Mirror Device), and a micro LED. The image based on the image light L1 is used to visually display various information such as a road guidance display, a distance to a vehicle ahead, a remaining battery level of the vehicle, and a current vehicle speed.

[0037] The optical system 3 guides the image light L1 output by the display element 2 to the visual field area Ac set for the user's eyes. In the visual field area Ac, the user can visually confirm the image formed by the display element 2 with his own eyes without being blocked. Hereinafter, in order to distinguish the image light emitted from the optical system 3 from the image light L1 output by the display element 2 toward the optical system 3, the image light emitted from the optical system 3 may be denoted by the reference symbol L2 as needed.

[0038] Figure 2 1 is an explanatory diagram of the optical path of the image light L2 emitted from the optical system 3 of the image display device 1. In this embodiment, the optical system 3 expands the visual field Ac by the effect of pupil dilation. That is, the optical system 3 expands the visual field Ac by copying the pupil of the image light L1. In this embodiment, the visual field Ac is defined by a rectangular plane. As long as the user D is within the visual field Ac, the user D can see the image even if the position of the user D's eyes is Figure 2 Even if the image is shifted in the horizontal and vertical directions, the image based on the image light L1 can be visually confirmed.

[0039] like Figure 1 As shown, the optical system 3 includes a light guide member 5 and a projection optical system 6 .

[0040] The light guide member 5 guides the image light L1 forming an image output from the display element 2 to the user's field of view area Ac as an optical image. In the present embodiment, the optical image is a virtual image Iv.

[0041] Figure 3 2 is a perspective view of a configuration example of the light guide member 5. When describing the light guide member 5, refer to Figure 3 The three axes XYZ orthogonal coordinates are described in .

[0042] like Figure 3 As shown, the light guide member 5 includes a main body 50 , an incident region 51 , an auxiliary expansion region 52 , and an emission expansion region 53 .

[0043] The main body 50 is formed of a material that is transparent in the visible light region. The main body 50 is in the shape of a plate. In the present embodiment, the main body 50 is in the shape of a rectangular plate. The main body 50 has a first surface 50a and a second surface 50b in the thickness direction of the main body 50. Figure 3 The main body 50 is configured with the first surface 50a facing the display element 2 side and the second surface 50b facing the field of view Ac side. In this case, the first surface 50a is the incident surface of the image light L1 entering the main body 50, and the second surface 50b is the exit surface of the image light L2 emitted from the main body 50. In the present embodiment, the light-guiding member 5 is positioned so that the image light L2 emitted from the main body 50 is reflected by the light-transmitting member and thereby guided to the field of view Ac as a virtual image Iv. Thus, the user D can view the virtual image Iv in a manner superimposed on the real scene that can be visually confirmed from the field of view Ac through the light-transmitting member. In the present embodiment, the light-transmitting member is the windshield 101, but the light-transmitting member is not limited to the windshield 101, and may be a member such as a combiner that is transparent (however, not limited to colorless and transparent) in the visible light region.

[0044] Figure 4 is a schematic top view of the light guide member 5. In particular, Figure 4 5 is a top view of the light guide member 5 as viewed from the second surface 50b side. Figure 4 As shown, the incident region 51 , the auxiliary expansion region 52 , and the emission expansion region 53 are formed in the main body 50 of the light guide member 5 .

[0045] The incident area 51 allows the image light L1 to enter the main body 50 so that the image light L1 propagates in the main body 50. In the present embodiment, the incident area 51 allows the image light L1 incident on the first surface 50a of the main body 50 from the first oblique direction inclined relative to the normal line of the first surface 50a of the main body 50 to enter the main body 50 so that the image light L1 propagates in the main body 50. In the present embodiment, Figure 3 In the embodiment, the first oblique direction is the direction indicated by D1. In the present embodiment, the incident area 51 causes the image light L1 to be incident on the main body 50 so that the image light L1 propagates in the main body 50 along a given direction (positive direction of the X-axis) in a plane (in the XY plane) perpendicular to the thickness direction of the main body 50. Figure 4, the image light propagating in the positive direction of the X-axis is marked with the reference symbol L1A. In the present embodiment, the incident area 51 is used for coupling between the display element 2 and the light guide member 5. The incident area 51 allows the image light L1 to be incident on the main body 50 so that the image light L1 propagates in the main body 50 under the condition of total reflection. The "coupling" mentioned here refers to the state of propagating in the main body 50 of the light guide member 5 under the condition of total reflection.

[0046] The incident area 51 is composed of a diffraction structure (periodic structure) having a diffraction effect on the image light L1. The diffraction structure of the incident area 51 is, for example, a volume hologram element (holographic diffraction grating). The volume hologram element produces a diffraction effect by periodic modulation of the refractive index. The diffraction pitch (diffraction period) of the volume hologram element represents the period of change of the refractive index of the volume hologram element. The diffraction period of the volume hologram element can be defined, for example, by the distance between the maximum refractive index or the minimum refractive index of the volume hologram element. The incident area 51 is, for example, formed inside the main body 50.

[0047] The incident area 51 causes the image light L1 to be incident on the main body 50 under the condition of being totally reflected by the first surface 50a and the second surface 50b by diffraction. The image light L1 is totally reflected by the first surface 50a and the second surface 50b by passing through the incident area 51, and thus travels in the main body 50 along the positive direction of the X axis.

[0048] The size of the incident area 51 is set so that part or all of the image light L1 from the display element 2 after passing through the projection optical system 6 is incident on the incident area 51. Figure 4 As shown, the incident area 51 is a quadrilateral.

[0049] The auxiliary expansion region 52 is arranged to be aligned with the incident region 51 in a given direction (positive direction of the X-axis). The auxiliary expansion region 52 is formed by a diffraction structure (periodic structure) having a diffraction effect on the image light L1A. The diffraction structure of the auxiliary expansion region 52 is, for example, a volume hologram element (holographic diffraction grating). The auxiliary expansion region 52 is formed, for example, inside the main body 50.

[0050] The auxiliary expansion region 52 changes the traveling direction of the image light L1A to the first propagation direction and divides it into a plurality of directions. The first propagation direction is a direction that intersects with a given direction in a plane (in an XY plane) that is orthogonal to the thickness direction of the main body 50. For example, the first propagation direction is the positive direction of the Y axis. Figure 4In the figure, the image light propagating in the positive direction of the Y axis is labeled with the reference symbol L1B. In this way, the auxiliary expansion area 52 is configured to divide the image light L1A propagating in a given direction into a plurality of image lights L1B propagating in a first propagation direction. The auxiliary expansion area 52 allows the plurality of image lights L1B arranged in a given direction (positive direction of the X axis) by dividing the image light L1A propagating in the main body 50 of the light guide member 5 to go to the exit expansion area 53. In this way, the auxiliary expansion area 52 expands the pupil of the image light L1 in the given direction (positive direction of the X axis). That is, as Figure 4 As shown, the auxiliary expansion region 52 expands the image light L1A by splitting it into a plurality of substantially parallel image lights L1B that travel to the exit expansion region 53 , thereby replicating the pupil of the image light L1 projected by the projection optical system 6 in a given direction (positive direction of the X axis).

[0051] The size of the auxiliary extension region 52 is set so that the image light L1A from the incident region 51 is incident on the auxiliary extension region 52. As an example, the end ( Figure 4 The size of the Y-axis direction of the incident area 51 (the right end in FIG. 1 ) is set so that the image light L1A diffracted by the incident area 51 is incident on the auxiliary expansion area 52 without leakage. Figure 4 As shown, the auxiliary expansion region 52 is quadrilateral.

[0052] The emission expansion region 53 is arranged to be parallel to the auxiliary expansion region 52 in the first propagation direction (positive direction of the Y axis). The emission expansion region 53 is formed by a diffraction structure (periodic structure) having a diffraction effect on the image light L1B. The diffraction structure of the emission expansion region 53 is, for example, a volume hologram element (holographic diffraction grating). The emission expansion region 53 is formed, for example, inside the main body 50.

[0053] The emission expansion region 53 changes the traveling direction of the image light L1B to the second propagation direction and divides it into a plurality of directions. The second propagation direction is the direction from the main body 50 to the field of view area Ac. Figure 3 In FIG. 5 , the image light propagating in the second propagation direction is labeled with reference symbol L12. The emission expansion region 53 causes the plurality of image lights L1C propagating in the second propagation direction to be emitted from the second surface 50b of the main body 50 in a second inclined direction inclined relative to the normal line of the second surface 50b of the main body 50. Figure 3 In FIG. 1 , the image light propagating in the second oblique direction is labeled with reference symbol L2. Figure 3In the figure, the second oblique direction is the direction represented by D1. Thus, the first oblique direction and the second oblique direction are parallel to each other. In this way, the emission expansion area 53 is configured to divide the image light L1B propagating along the first propagation direction into a plurality of image lights L2 propagating along the second propagation direction and emitted from the second surface 50b of the main body 50 along the second oblique direction. The emission expansion area 53 allows the plurality of image lights L2 arranged along the first propagation direction (positive direction of the Y axis) by dividing the image light L1B propagating in the main body 50 of the light-guiding member 5 to proceed to the field of view area Ac. In this way, the emission expansion area 53 expands the pupil of the image light L1 in the first propagation direction (positive direction of the Y axis). That is, as Figure 3 As shown, the emission expansion area 53 expands the pupil of the image light L1 projected by the projection optical system 6 by replicating it in the first propagation direction (positive direction of the Y axis) by dividing the image light L1B into a plurality of substantially parallel image lights L2 heading to the field of view area Ac.

[0054] In this way, the auxiliary expansion area 52 and the emission expansion area 53 expand the image light L1 incident from the incident area 51 into the main body 50 of the light guide member 5 by dividing it in a given direction (positive direction of the X axis) and in the first propagation direction (positive direction of the Y axis), thereby replicating the pupil of the image light L1. In the present embodiment, the given direction corresponds to the horizontal direction of the field of view Ac, and the first propagation direction corresponds to the vertical direction of the field of view Ac. In the present embodiment, the auxiliary expansion area 52 and the emission expansion area 53 expand the image light L1 incident from the incident area 51 into the main body 50 of the light guide member 5 by dividing it into a plurality of image lights L2 and emitting them to the field of view Ac, thereby replicating the pupil of the image light L1. In the present embodiment, the plurality of image lights L2 are parallel to each other. "The plurality of image lights L2 are parallel to each other" is not limited to a strict meaning that the plurality of image lights L2 are parallel to each other, but includes the plurality of image lights L2 being substantially parallel to each other. Even if the plurality of image lights L2 are not parallel to each other in a strict sense, it is sufficient as long as the directions of the plurality of image lights L2 are consistent to the extent that the plurality of image lights L2 can be considered to be parallel in optical design. By making the plurality of image lights L2 parallel to each other, the uniformity of the configuration of the pupil of the image light can be improved in the field of view area Ac, thereby improving the filling rate of the pupil of the image light in the field of view area Ac. The lower the filling rate of the pupil, the more light and dark increase in the optical image (virtual image Iv) observed from the field of view area AC, which becomes a cause of the deterioration of the image quality. By improving the filling rate of the pupil of the image light in the field of view area Ac, the image quality of the optical image (virtual image Iv) can be improved.

[0055] like Figure 2As shown, in this embodiment, the plurality of image lights L2 are reflected by the windshield 101 and travel to the visual field area Ac. The light guide member 5 may be configured to make the plurality of image lights L2 reflected by the windshield 101 and travel to the visual field area Ac parallel to each other. Figure 2 In the case where the windshield 101 is a curved surface, even if the direction to the windshield 101 is the same, the incident angle and the reflection angle of the image light L2 will be different depending on the location within the surface of the windshield 101. Therefore, the light guide member 5 is not configured so that the plurality of image lights L2 are parallel to each other until they are emitted from the light guide member 5 and incident on the windshield 101, but is configured so that they become parallel to each other by being reflected by the windshield 101. On the other hand, in the case where the windshield 101 is a flat surface, if the direction to the windshield 101 is the same, the incident angle and the reflection angle of the image light L2 are equal regardless of the location within the surface of the windshield 101. Therefore, the light guide member 5 can be configured so that a plurality of image lights L2 that are parallel to each other are emitted from the light guide member 5.

[0056] In particular, in this embodiment, if Figure 3 As shown, the emission expansion region 53 causes the image light L1B incident on the emission expansion region 53 and propagating along the first propagation direction to be branched into the first image light L11, the second image light L12, and the third image light L13 in a given plane P1 including the first propagation direction and the second propagation direction. The given plane P1 corresponds to Figure 3 YZ plane.

[0057] The portion in the emission expansion region 53 where the image light L1B is branched into the first image light L11, the second image light L12, and the third image light L13 may be any portion of the emission expansion region 53, but may be included in the optical path of the image light L1 from the incident region 51 to the emission expansion region 53, at the end of the emission expansion region 53 on the incident region 51 side. In the present embodiment, the optical path of the image light L1 from the incident region 51 to the emission expansion region 53 passes through the auxiliary expansion region 52. Thus, for example, in Figure 4In the figure, "the end of the exit expansion region 53 on the incident region 51 side in the optical path of the image light L1 from the incident region 51 to the exit expansion region 53" is not the end of the exit expansion region 53 on the negative direction side of the X axis, but the end on the negative direction side of the Y axis. Here, the end of the exit expansion region 53 on the incident region 51 side may be a region that occupies 1 / 4 of the exit expansion region 53 in the first propagation direction from the end 531 on the incident region 51 side of the exit expansion region 53. On the optical path of the image light L1 from the incident region 51 to the exit expansion region 53, the end of the exit expansion region 53 on the incident region 51 side is the end on the side where the image light is incident in the exit expansion region 53, so it is the part in the exit expansion region 53 where the amount of image light L1B incident on the exit expansion region 53 is large. Therefore, by generating the third image light L13 in the portion where the amount of the image light L1B incident on the emission expansion region 53 is large, the filling rate of the pupil of the image light L1 can be efficiently improved. In particular, the emission expansion region 53 can at least branch the image light L1B initially incident on the emission expansion region 53 from the incident region 51 into the first image light L11, the second image light L12, and the third image light L13. Of course, the light guide member 5 can branch the image light L1B into the first image light L11, the second image light L12, and the third image light L13 at a plurality of locations.

[0058] Figure 5 is a partial schematic cross-sectional view of the light guide member 5. In particular, Figure 5 1 is a schematic cross-sectional view of a portion of the main body 50 of the light guide member 5 including the emission expansion region 53 in a given plane P1. Figure 5 In the embodiment, the image light L1B enters the emission expansion region 53 from the first surface 50 a side of the main body 50 .

[0059] Figure 5 The first image light L11 is at a first angle θ o1 The light is emitted from the emission expansion region 53. The first angle θ o1 The conditions for propagation by total reflection in the main body 50 are met. Figure 5 The first image light L11 propagates in the main body 50 along the first propagation direction (positive direction of the Y axis) under the condition of total reflection. o1 The propagation angle θ of the image light L1 propagating from the incident area 51 to the exit expansion area 53 in the given plane P1 i In this embodiment, on the optical path of the image light L1, there is an auxiliary expansion region 52 between the incident region 51 and the emission expansion region 53, so the propagation angle θ i The propagation angle is equal to that of the image light L1B propagating from the auxiliary expansion region 52 to the emission expansion region 53 . Figure 5The first image light L11 corresponds to the 0th-order diffracted light with respect to the image light L1B.

[0060] Figure 5 The second image light L12 is at a second angle θ o2 The light is emitted from the emission expansion region 53. The second angle θ o2 With the first angle θ o1 Different. The second angle θ o2 The condition of propagation by total reflection in the main body 50 is not satisfied. Figure 5 The second image light L12 is emitted from the main body 50. In the present embodiment, the second image light L12 is refracted when emitted from the second surface 50b of the main body 50, and is emitted as the image light L20. Figure 5 The second image light L12 corresponds to the first-order diffracted light with respect to the image light L1B.

[0061] Figure 5 The third image light L13 is at a third angle θ p The light is emitted from the emission expansion region 53. p With the first angle θ o1 and the second angle θ o2 Different. The third angle θ p The conditions for propagation by total reflection in the main body 50 are met. Figure 5 The third image light L13 propagates in the main body 50 along the first propagation direction (the positive direction of the Y axis) under the condition of total reflection. Figure 5 The third image light L13 corresponds to the -1st order diffracted light with respect to the image light L1B.

[0062] In the emission expansion area 53, the second image light L12 is emitted from the main body 50 and finally reaches the field of view area Ac as the image light L20. On the other hand, the first image light L11 and the third image light L13 propagate in the main body 50 along the first propagation direction (positive direction of the Y axis) under the condition of total reflection. Therefore, the first image light L11 and the third image light L13 can be diffracted by the diffraction structure of the emission expansion area 53. That is, the first image light L11 and the third image light L13 can be further branched into new first image light L11, second image light L12, and third image light L13.

[0063] exist Figure 5In the figure, the focus is on the first image light L11. After being emitted from the emission expansion area 53, the first image light L11 is totally reflected by the second surface 50b of the main body 50, passes through the emission expansion area 5 and is totally reflected by the first surface 50a of the main body 50, and enters the emission expansion area 53 from the first surface 50a side of the main body 50. The first image light L11 is branched into the first image light, the second image light, and the third image light by the emission expansion area 53. The so-called branching of the first image light L11 into the first image light means that the first image light L11 goes straight as it is in the emission expansion area 53. That is, a part of the first image light L11 goes straight as it is, another part of the first image light L11 changes direction to become the second image light L12a, and another part of the first image light L11 changes direction to become the third image light (in Figure 5 The second image light L12a is refracted when emitted from the second surface 50b of the main body 50, and is emitted as the image light L2a.

[0064] Furthermore, the first image light L11 that travels straight as it is in the emission expansion area 53 is totally reflected by the second surface 50b of the main body 50, passes through the emission expansion area 53 and is totally reflected by the first surface 50a of the main body 50, and enters the emission expansion area 53 again from the first surface 50a side of the main body 50. The first image light L11 is branched into the first image light, the second image light, and the third image light by passing through the emission expansion area 53. That is, a part of the first image light L1 travels straight as it is, another part of the first image light L11 changes direction and becomes the second image light L12b, and another part of the first image light L11 changes direction and becomes the third image light (in Figure 5 The second image light L12b is refracted when emitted from the second surface 50b of the main body 50, and is emitted as the image light L2b.

[0065] exist Figure 5 In the figure, the third image light L13 is focused on. After being emitted from the emission expansion area 53, the third image light L13 is totally reflected by the second surface 50b of the main body 50, passes through the emission expansion area 53, is totally reflected by the first surface 50a of the main body 50, and enters the emission expansion area 53 from the first surface 50a side of the main body 50. The third image light L13 is branched into the first image light, the second image light, and the third image light by the emission expansion area 53. The so-called branching of the third image light L13 into the third image light means that the third image light L13 goes straight as it is in the emission expansion area 53. That is, a part of the third image light L13 goes straight as it is, another part of the third image light L13 changes direction to become the second image light L12c, and another part of the third image light L13 changes direction to become the first image light (in Figure 5The second image light L12c is refracted when emitted from the second surface 50b of the main body 50, and is emitted as the image light L2c. For the third image light L13, the first image light is equivalent to the first-order diffracted light, and the second image light is equivalent to the second-order diffracted light.

[0066] exist Figure 5 In FIG. 1 , the central light rays of the image lights L1B, L11, L12, L12a, L12b, L12c, L13, L20, L2a, L2b, and L2b are indicated by arrows. As described above, the image light L1 is actually light having an angle equivalent to the viewing angle. Figure 5 , for a part of the image lights L11 and L13 and the image lights L12b, L12c, L20, L2a, L2b, and L2c, in addition to the central light, their ranges F11, F13, F12b, F12c, F2, F2a, F2b, and F2c are also illustrated.

[0067] exist Figure 5 In the embodiment, a plurality of image lights L20, L2a, L2b, and L2c are emitted from the second surface 50b of the main body 50 through the emission expansion area 53. The intervals between the plurality of image lights L20, L2a, and L2b are equal, and the gaps G1 between the ranges of adjacent image lights among the plurality of image lights L20, L2a, and L2b are equal. By narrowing the gap G1, the filling rate of the pupil of the image light L1 in the field of view area Ac can be increased.

[0068] Figure 5 The emission expansion area 53 includes an overlapping portion 53a where the first image light L11 and the third image light L13 are incident in a partially overlapping state within a given plane P1. Therefore, the second image light L12b branched from the first image light L11 at the overlapping portion 53a and the second image light L12c branched from the third image light L13 at the overlapping portion 53a are also in a partially overlapping state and are emitted from the second surface 50b of the main body 50 to the outside as image lights L2b and L2c. Therefore, the image lights L2b and L2c are also in a partially overlapping state. Figure 5 In the figure, image light L2c is closer to image light L2a than image light L2b, and gap G2 between ranges F2a and F2c of image light L2a and L2c is narrower than gap G1 between ranges F2a and F2b of image light L2a and L2b. Multiple image lights L20, L2a, L2b, and L2c are all image light L2. Therefore, the interval between image light L2 is actually narrowed, which can improve the filling rate of the pupil of image light L1 in field of view area Ac. The difference G3 between gap G1 and gap G2 is equal to the distance between the incident positions of the first image light L11 and the third image light L13 at the overlapping portion 53a.

[0069] Since the image lights L2b and L2c partially overlap at the overlapping portion 53a, the image lights L2b and L2c may interfere with each other. If the image lights L2b and L2c interfere with each other, the quality of the virtual image Iv may be reduced. Therefore, the emission expansion area 53 is set so that the optical path length difference between the first image light L11 and the third image light L13 incident on the overlapping portion 53a is longer than the coherence length of the image light L1. As a result, the possibility of interference between the image lights L2b and L2c is reduced, and the degradation of the quality of the virtual image Iv can be reduced.

[0070] Figure 6 is an explanatory diagram of the coherence length of the image light L1. Figure 6 In the equation, λ is the central wavelength of the image light L1 [μm], and Δλ is the line width of the image light L1 [μm]. In the present embodiment, the line width is the half-value full width of the spectrum of the image light L1. That is, it is the width of the spectrum when the intensity of the image light L1 becomes Ap / 2, which is half of the maximum value Ap. In a vacuum, the coherence length is λ 2 / Δλ. If the refractive index of the main body 50 of the light guide member 5 is n, the coherence length of the image light L1 in the main body 50 is (λ / n) 2 / (Δλ / n).

[0071] exist Figure 5 In the figure, one overlapping portion 53a is shown, but the emission expansion region 53 may include more than two overlapping portions 53a.

[0072] Figure 7 1 is an explanatory diagram of a pattern of diffraction of image light by the emission expansion region 53 of the light guide member 5. Figure 7 , the above-mentioned modes A to D in the given plane P1 are illustrated. In the modes A to D, the position P0 is the position where the image light L1B first enters the emission expansion area 53. At the position P0, the image light L1Bb is branched into the first image light L11, the second image light L12, and the third image light L13.

[0073] Figure 7Mode A shows the first image light L11 propagating in the main body 50. In mode A, after being emitted from the emission expansion area 53, the first image light L11 is totally reflected between the first surface 50a and the second surface 50b of the main body 50, and propagates in the main body 50 along the first propagation direction. The first image light L11 enters the emission expansion area 53 from the first surface 50a side of the main body 50 at each of the positions P11, P12, P13, P14, and P15, and is branched into the first image light L11, the second image light L12, and the third image light (not shown). In mode A, the second image light L12 from the positions P11, P12, P13, P14, and P15 is taken out from the second surface 50b of the main body 50 to the outside as image light L2.

[0074] Figure 7 Modes B to D show how the third image light L13 propagates in the main body 50. In modes B to D, after being emitted from the emission expansion region 53, the third image light L13 is totally reflected between the first surface 50a and the second surface 50b of the main body 50, and propagates in the main body 50 along the first propagation direction.

[0075] In patterns B to D, the third image light L13 enters the emission expansion region 53 from the first surface 50 a side of the main body 50 at position P31 and is branched into the first image light L11 , the second image light L12 , and the third image light L12 .

[0076] In the patterns B and D, the first image light L11 branched from the third image light L13 at the position P31 is totally reflected between the first surface 50a and the second surface 50b of the main body 50 after being emitted from the emission expansion region 53, and propagates along the first propagation direction in the main body 50. Thereafter, the first image light L11 enters the emission expansion region 53 from the first surface 50a side of the main body 50 at the position P16, and is branched into the first image light L11, the second image light L12, and the third image light L13.

[0077] In mode B, the first image light L11 branched from the third image light L13 at position P16 is totally reflected between the first surface 50a and the second surface 50b of the main body 50 after being emitted from the emission expansion area 53, and propagates in the main body 50 along the first propagation direction. The first image light L11 enters the emission expansion area 53 from the first surface 50a side of the main body 50 at each of positions P17 and P18, and is branched into the first image light L11, the second image light L12, and the third image light (not shown). In mode B, the second image light L12 from positions P31, P16, P17, and P18 is taken out from the second surface 50b of the main body 50 to the outside as image light L2.

[0078] In mode D, at position P16, after the third image light L13 is emitted from the emission expansion region 53, it is totally reflected between the first surface 50a and the second surface 50b of the main body 50, and propagates in the main body 50 along the first propagation direction. At position P19, the third image light L13 enters the emission expansion region 53 from the first surface 50a side of the main body 50, and is branched into the first image light (not shown), the second image light L12, and the third image light L13. In mode D, the second image light L12 from the positions P31, P16, and P19 is taken out from the second surface 50b of the main body 50 to the outside as image light L2.

[0079] In mode C, at position P31, after the third image light L13 is emitted from the emission expansion region 53, it is totally reflected between the first surface 50a and the second surface 50b of the main body 50, and propagates along the first propagation direction in the main body 50. Thereafter, at position P32, the third image light L13 enters the emission expansion region 53 from the first surface 50a side of the main body 50, and is branched into the first image light L11, the second image light L12, and the third image light (not shown). Figure 7 In mode C, the first image light L11 branched from the third image light L13 at position P32 is totally reflected between the first surface 50a and the second surface 50b of the main body 50 after being emitted from the emission expansion area 53, and propagates along the first propagation direction in the main body 50. The first image light L11 enters the emission expansion area 53 from the first surface 50a side of the main body 50 at position P19, and is branched into the first image light L11, the second image light L12, and the third image light (not shown). In mode C, the second image light L12 from positions P31, P32, and P19 is taken out from the second surface 50b of the main body 50 as image light L2.

[0080] exist Figure 7 In the case of the first image light L11 incident on the position P12 and the third image light L13 incident on the position P31, there is a possibility that they partially overlap in the given plane P1. That is, there may be an overlapping portion 53a in the range including the positions P12 and P31. Figure 7 In the case of the first image light L11 incident on the position P14 and the third image light L13 incident on the position P32, there is a possibility that they partially overlap in the given plane P1. That is, there may be an overlapping portion 53a in the range including the positions P14 and P32. Figure 7 In the example, the first image light L11 incident on the position P15 and the third image light L13 incident on the position P19 may partially overlap in the given plane P1. That is, an overlapping portion 53a may exist in the range including the positions P15 and P19.

[0081] exist Figure 7 In the case of the first image light L11 incident on the position P13 and the first image light L11 incident on the position P16, there is a possibility that the first image light L11 partially overlaps in the given plane P1. Figure 7 In the case of the first image light L11 incident on the position P14 and the first image light L11 incident on the position P17, there is a possibility that the first image light L11 partially overlaps in the given plane P1. Figure 7 In the embodiment, the first image light L11 incident on the position P15 and the first image light L11 incident on the position P18 or the position P19 may be in a state of partially overlapping in the given plane P1. That is, in addition to the overlapping portion 53 where the first image light L11 and the third image light L13 may be incident in a state of partially overlapping in the given plane P1, the emission expansion area 53 may also include an overlapping portion where the first image light L11 and the first image light L11 branched from the third image light L13 may be incident in a state of partially overlapping in the given plane P1. That is, the emission expansion area 53 may have an overlapping portion where the first or third image light branched from the first image light L11 and the first or third image light branched from the third image light L13 may be incident in a state of partially overlapping in the given plane P1. As a result, the interval of the image light L2 is substantially narrowed, and the filling rate of the pupil of the image light L1 in the field of view area Ac can be increased, thereby improving the image quality.

[0082] Figure 8This is an explanatory diagram of an example of diffraction of image light by the emission expansion area 53 of the light guide member 5. In the present embodiment, the emission expansion area 53 branches at least the image light L1B initially incident on the emission expansion area 53 from the incident area 51 into the first image light L11, the second image light L12, and the third image light L13 (refer to the position P0). The emission expansion area 53 branches the first image light L11 that has traveled back and forth an arbitrary number of times in the emission expansion area 53 into the first image light L11, the second image light L12, and the third image light L13 (refer to the positions P11, P12, P13, P14, and P15). The number of round trips m1 of the first image light L11 at the positions P11, P12, P13, P14, and P15 are 1, 2, 3, 4, and 5, respectively. The emission expansion region 53 branches the third image light L13 that has traveled back and forth an arbitrary number of times in the emission expansion region 53 into the first image light L11, the second image light L12, and the third image light L13 (refer to positions P31 and P32). The number of round trips m2 of the first image light L11 at positions P31 and P32 is 1 and 2, respectively. The number of round trips refers to the number of times the first image light or the third image light is emitted from the emission expansion region 53 and returns to the emission expansion region 53 after being reflected by the first surface 50a and the second surface 50b of the main body 50. That is, the image light L1B enters the emission expansion region 53 at position P0, and the number of round trips of the first image light becomes 1, 2, 3...times at positions P11, P12, P13..., and the number of round trips of the third image light becomes 1, 2...times at positions P31, P32...

[0083] The light guide member 5 described above is configured to satisfy the following formula (1), the following formula (2), and the following formula (3).

[0084] [Mathematical formula 1]

[0085]

[0086] [Mathematical formula 2]

[0087]

[0088] [Mathematical formula 3]

[0089]

[0090] Regarding formula (1), θ i is the propagation angle [°]. o is the angle [°] at which the second image light L12 is emitted from the main body 50 , and n is the refractive index of the main body 50 .

[0091] Regarding formula (2), θ pis the third angle [°]. T is the thickness of the main body 50 [μm]. m1 is the number of round trips of the first image light L11 in the emission expansion area 53 when incident on the overlapping portion 53a. m2 is the number of round trips of the third image light L13 in the emission expansion area 53 when incident on the overlapping portion 53a. Both m1 and m2 are positive integers.

[0092] Regarding formula (3), θ i0 is the propagation angle [°] of the central ray of the image (virtual image Iv) visually recognized by the observer (user D). i0 θ is the propagation angle of the central ray of image light L1. f1 and θ f2 are all positive values ​​[°]. In particular, θ f1 is the specified propagation angle θ i The upper limit value of the range [°], the propagation angle θ i The upper limit of the range is given by θ i0 +θ f1 Indicates. θ f2 is the specified propagation angle θ i The lower limit value of the range [°], the propagation angle θ i The lower limit of the range is given by θ i0 -θ f2 In other words, the propagation angle θ i The range is θ i0 -θ f2 Above and θ i0 +θ f1 Hereinafter, d is the diffraction pitch [μm] of the diffraction structure of the emission expansion region 53 .

[0093] First, refer to Figure 5 Formula (1) is explained. By making the light guide member 5 satisfy the above formula (1), the emission expansion area 53 can make the image light L1B incident on the emission expansion area 53 and propagating along the first propagation direction be branched into the first image light L11, the second image light L12 and the third image light L13 in a given plane P1 including the first propagation direction and the second propagation direction. In addition, the first image light L11 and the third image light L13 can propagate along the first propagation direction in the main body 50, and the second image light L12 can be emitted from the main body 50 to the outside.

[0094] The first angle θ of the first image light L11 o1 The condition that the light is totally reflected and propagated in the main body 50 is satisfied. As described above, the light is equivalent to the 0th order diffracted light with respect to the image light L1B. That is, the first angle θ o1 The propagation angle θ of the image light L1 propagating from the incident area 51 to the exit expansion area 53 in the given plane P1 iTherefore, according to the total reflection condition of Snell's law, the propagation angle θ i It is set to satisfy the following formula (4).

[0095] [Formula 4]

[0096]

[0097] As described above, the second image light L12 corresponds to the first-order diffracted light with respect to the image light L1B, and the third image light L13 corresponds to the −1st-order diffracted light with respect to the image light L1B. Diffraction by the emission expansion region 53 is expressed by the following equation (5).

[0098] [Formula 5]

[0099]

[0100] In equation (5), m is the diffraction order. m is the emission angle of the image light emitted from the emission expansion area 53 within the given plane P1. n_in is the refractive index of the medium on the incident side relative to the emission expansion area 53. n_out is the refractive index of the medium on the emission side relative to the emission expansion area 53. In the present embodiment, the medium on the incident side relative to the emission expansion area 53 and the medium on the emission side relative to the emission expansion area 53 are both the main body 50 of the light guide member 5. Therefore, n_in and n_out are equal to the refractive index n of the main body 50. Therefore, the following formula (6) can be obtained based on the above formula (5).

[0101] [Mathematical formula 6]

[0102]

[0103] The second image light L12 is a first-order diffracted light with respect to the image light L1B, and m=1 in the second image light L12. In addition, for the second image light L12, the emission angle θ is m is the second angle θ o2 Therefore, the following equation (7) holds true for the second image light L12.

[0104] [Formula 7]

[0105]

[0106] The third image light L13 is a diffracted light of the -1st order with respect to the image light L1B, and m=-1 in the third image light L13. In addition, for the third image light L13, the emission angle θ is m is the third angle θ p Therefore, the following formula (8) holds true for the third image light L13.

[0107] [Mathematical formula 8]

[0108]

[0109] The condition for the existence of the third image light L13 and θ p Based on the above, the condition for the existence of the third image light L13 is given by the following formula (9).

[0110] [Mathematical formula 9]

[0111]

[0112] According to equation (8) and equation (9), the following equation (10) can be obtained.

[0113] [Formula 10]

[0114]

[0115] According to equation (7) and equation (10), the following equation (11) can be obtained.

[0116] [Mathematical formula 11]

[0117]

[0118] The second image light L12 is emitted from the emission expansion area 53 at the second angle θ o2 The angle θ with respect to the second image light L12 emitted from the main body 50 o The following formula (12) holds.

[0119] [Mathematical formula 12]

[0120]

[0121] According to equation (11) and equation (12), the following equation (13) can be obtained.

[0122] [Mathematical formula 13]

[0123]

[0124] According to equation (4) and equation (13), the above equation (1) can be obtained.

[0125] Next, refer to Figure 6 as well as Figure 8 Formula (2) is explained. Formula (2) represents the condition that the optical path length difference between the first image light L11 and the third image light L13 incident on the overlapping portion 53a is longer than the coherence length of the image light L1. That is, by satisfying Formula (2), the interference of the image lights L2b and L2c is reduced, and the degradation of the image quality of the virtual image Iv can be reduced.

[0126] As reference Figure 6 As described above, the right side of the equation (2) represents the coherence length of the image light L1.

[0127] The optical path length of the first image light L11 incident on the overlapping portion 53 a is expressed by the following equation (14).

[0128] [Formula 14]

[0129]

[0130] The optical path length of the third image light L13 incident on the overlapping portion 53 a is expressed by the following equation (15).

[0131] [Mathematical formula 15]

[0132]

[0133] Therefore, the condition that the optical path length difference between the first image light L11 and the third image light L13 incident on the overlapping portion 53 a is longer than the coherence length of the image light L1 is expressed by the above formula (2).

[0134] Next, refer to Fig. 9 Let’s explain equation (3). For equation (3), let the propagation angle θ i The range is θ i0 -θ f2 Above and θ i0 +θ f1 As an example, in this embodiment, θ io is the propagation angle of the central ray of image light L1, θ f1 ,θ f2 is a positive value. In particular, θ i0 -θ f2 is the propagation angle of the light corresponding to the upper side of the viewing angle of the image light L1, that is, the upper end of the viewing area Ac. As an example, in this embodiment, θ i0 +θ f1 It is the propagation angle of the light corresponding to the lower side of the viewing angle of the image light L1, that is, the lower end of the viewing area Ac.

[0135] exist Fig. 9 In the figure, the image light L111 has a propagation angle of θ i0 The image light L112 has a propagation angle of θ i0 -θ f2 The image light L113 has a propagation angle of θ i0 +θ f1 Image light. Fig. 9, image light L121 is the second image light for image light L111 , image light L122 is the second image light for image light L112 , and image light L123 is the second image light for image light L113 .

[0136] exist Fig. 9 In the case where the image light L112 and the image light L123 overlap, the image light L112 does not propagate in the main body 50 along the first propagation direction but is taken out of the main body 50 to the outside, or the image light L123 does not propagate from the main body 50 to the outside but propagates in the main body 50 along the first propagation direction. i Within the range, the image light L1 will not propagate correctly, the given viewing angle of the image light L1 cannot be maintained, and the image quality of the virtual image Iv may be reduced.

[0137] As per Fig. 9 As understood, for a certain propagation angle θ i The second image light L12 and the other propagation angle θ i The condition for the first image light L11 not to overlap is that the second angle θ of the image light L123 o2 Smaller than the propagation angle θ of the image light L112 i0 -θ f2 .

[0138] Here, for the sake of convenience, the diffraction spacing d is assumed to be a positive value, and thus the following equation (16) is used instead of the above equation (6).

[0139] [Formula 16]

[0140]

[0141] According to the above formula (16), the second angle θ of the image light L123 is o2 It is expressed by the following formula (17).

[0142] [Mathematical formula 17]

[0143]

[0144] At the second angle θ of the image light L123 o2 Smaller than the propagation angle θ of the image light L112 i0 -θ f2 In the case of , the following formula (18) holds.

[0145] [Mathematical formula 18]

[0146]

[0147] According to equation (17) and equation (18), the following equation (19) can be obtained.

[0148] [Mathematical formula 19]

[0149]

[0150] If equation (19) is rearranged with respect to the diffraction spacing d, the following equation (20) can be obtained.

[0151] [Mathematical formula 20]

[0152]

[0153] According to the above formula (16), at the propagation angle θ i is the propagation angle θ of the central ray of image light L1 i0 In the case of , the condition for the existence of -1 order diffracted light is expressed by the following equation (21).

[0154] [Mathematical formula 21]

[0155]

[0156] If equation (21) is rearranged with respect to the diffraction spacing d, the following equation (22) can be obtained.

[0157] [Mathematical formula 22]

[0158]

[0159] According to equation (20) and equation (22), the above equation (3) can be obtained.

[0160] As described above, in the light guide member 5, the emission expansion area 53 includes the overlapping portion 53a where the first image light L11 and the third image light L13 are incident in a state of partially overlapping in the given plane P1. Therefore, the interval between the image lights L2 is narrowed, and the filling rate of the pupil of the image light L1 in the field of view area Ac can be improved.

[0161] Below, refer to Figure 10 to Figure 13 Reference Examples 1 to 4 of the present invention briefly describe conventional methods for increasing the filling rate of the pupil of the image light L1 in the field of view area Ac. In addition, among Reference Examples 1 to 4, Reference Example 1 shows an example in which the filling rate of the pupil of the image light L1 is low because the method for increasing the filling rate of the pupil of the image light L1 is not adopted.

[0162] Fig.10 This is an explanatory diagram of an example of diffraction of image light by the light guide member 501 of Reference Example 1. Fig.10 The light guide member 501 includes a main body 50, an incident area 51, an auxiliary expansion area 52, and an emission expansion area 530. Fig.10In order to simplify the illustration, the auxiliary expansion region 52 is omitted. Fig.10 The emission expansion region 530 is configured to divide the image light L1B propagating in the first propagation direction into a plurality of image lights L2 propagating in the second propagation direction and emitted from the second surface 50b of the main body 50 in the second oblique direction. Fig.10 In the figure, there are gaps between the image lights L2, and the filling rate of the pupil of the image light L1 is low.

[0163] Fig.11 This is an explanatory diagram of an example of diffraction of image light by the light guiding member 502 of Reference Example 2. Fig.11 The light guide member 502 and Fig.10 The light guide member 501 is larger than the incident area 51. Fig.11 In the incident area 51, the size D51 of the incident area 51 in the first propagation direction is greater than Fig.10 The incident area 51 of the image light L1 can be enlarged. Fig.11 The light guide member 502 and Fig.10 Compared with the light guide member 501 of FIG. 5 , the interval of the image light L2 is narrowed, and the filling rate of the pupil of the image light L1 can be improved. Fig.11 If the size of the incident area 51 is increased in this way, it is necessary to ensure a space for the incident area 51, so it is necessary to increase the size of the main body 50. In addition, it is necessary to emit a wide image light, so the display element 2 is also increased. As a result, the size of the optical system 3 and the size of the image display device 1 itself are also increased, and there is also a concern that the layout of the image display device 1 is restricted.

[0164] Fig.12 This is an explanatory diagram of an example of diffraction of image light by the light guiding member 503 of Reference Example 3. Fig.12 The light guide member 503 and Fig.10 The light guide member 501 is thinner than the thickness T of the main body 50. As a result, the distance that the image light L1B travels between the first surface 50a and the second surface 50b of the main body 50 is shortened, and the interval at which the image light L1B is taken out from the main body 50 in the first propagation direction is narrowed. Fig.12 The light guide member 503 and Fig.10 Compared with the light guide member 501 of FIG. 5 , the interval of the image light L2 is narrowed, and the filling rate of the pupil of the image light L1 can be improved. Fig.12 In this way, if the thickness T of the main body 50 is reduced, various problems may occur, such as an increase in the difficulty of material processing of the light guide member 503 , a decrease in the strength of the light guide member 503 , and an increase in the influence on the vibration of the light guide member 503 .

[0165] Fig.13This is an explanatory diagram of an example of diffraction of image light by the light guiding member 504 of Reference Example 4. Fig.13 The light guide member 504 and Fig.10 The refractive index n of the light guide member 501 is higher than that of the main body 50. As a result, the propagation angle of the image light L1B becomes smaller, and the interval of taking out the image light L1B from the main body 50 in the first propagation direction becomes narrower. Fig.13 The light guide member 504 and Fig.10 Compared with the light guide member 501, the interval of the image light L2 is narrowed, and the filling rate of the pupil of the image light L1 can be improved. However, the refractive index of the material that can be used for the main body 50 is limited, and there is a limit to the improvement of the filling rate by the refractive index.

[0166] In the present embodiment, in the light guide member 5, even without adopting the conventional method such as changing the size of the incident area 51, changing the thickness T of the main body 50 of the light guide member 5, and changing the refractive index n of the main body 50 of the light guide member 5, the interval of the image light L2 can be narrowed, and the pupil leakage filling of the image light L1 in the field of view area Ac can be reduced. In particular, the increase in the size of the incident area 51 leads to the increase in the size of the optical system 3 and the image display device 1. In the light guide member 5, it is not necessary to increase the size of the incident area 51 in order to reduce the pupil leakage filling of the image light L1 in the field of view area Ac, and the size of the incident area 51 can be reduced. In addition, in the overlapping portion 53a, the image lights L2b and L2c are partially overlapped, but the optical path length difference between the first image light L11 and the third image light L13 incident on the overlapping portion 53a is longer than the coherence length of the image light L1, so that the interference of the image lights L2b and L2c does not occur, and the degradation of the image quality of the virtual image Iv can be reduced.

[0167] The projection optical system 6 projects the image light L1 output from the display element 2 to form an image. Thus, the projection optical system 6 causes the image light L1 from the display element 2 to enter the light guide member 5. Figure 1 As shown, the projection optical system 6 is located between the display element 2 and the light guide member 5. The projection optical system 6, for example, collimates the image light L1 from the display element 2 and makes it incident on the incident area 51. The projection optical system 6 makes the image light L1 substantially collimated light and makes it incident on the incident area 51. The projection optical system 6 is, for example, a biconvex lens.

[0168] As described above, the image light L1 enters the optical system 3 as light having an angle substantially equivalent to the viewing angle. Figure 3, the irradiation area A10 of the image light L1 in the incident area 51 has a first size a1 and a second size a2. The first size a1 is the size of the irradiation area A10 in the first propagation direction (the positive direction of the Y axis). The second size a2 is the size of the irradiation area A10 in the direction (the direction of the X axis) that is orthogonal to the thickness direction of the main body 50 and the first propagation direction. In the present embodiment, the first size a1 is smaller than the second size a1. That is, the viewing angle of the image light L1 is smaller in the direction corresponding to the first propagation direction (for example, the vertical direction of the field of view Ac) than in the direction corresponding to the thickness direction of the main body 50 and the direction orthogonal to the first propagation direction (the direction of the X axis) (for example, the horizontal direction of the field of view Ac). Thus, compared to the case where the first size a1 is larger than the second size a2, the distance between the pupils of the image light L1 can be reduced in the first propagation direction. Therefore, the leakage filling of the pupil of the image light L1 in the field of view Ac can be reduced, and the size of the incident area 51 can be reduced. Figure 3 In FIG. 1 , the irradiation area A10 is an ellipse, the first dimension a1 corresponds to the minor axis, and the second dimension a2 corresponds to the major axis. The irradiation area A10 is not limited to an ellipse, and may be a rectangular shape in which the first dimension a1 is smaller than the second dimension a2.

[0169] The control device 4 can be implemented by semiconductor elements and the like. The control device 4 can be configured, for example, by a microcomputer, a CPU, an MPU, a GPU, a DSP, an FPGA or an ASIC. The control device 4 implements a predetermined function by reading the data and programs stored in the storage device 4a and performing various calculations. The storage device 4a is a storage medium that stores the programs and data required to implement the functions of the control device 4. The storage device 4a can be implemented, for example, by a hard disk (HDD), an SSD, a RAM, a DRAM, a ferroelectric memory, a flash memory, a disk or a combination thereof. A plurality of image data representing a virtual image Iv is stored in the storage device 4a. The control device 4 determines the displayed virtual image Iv based on the vehicle-related information obtained from the outside. The control device 4 reads the determined image data of the virtual image Iv from the storage device 4a and outputs it to the display element 2.

[0170] [1.2. Examples and Comparative Examples]

[0171] Hereinafter, examples and comparative examples of the light guide member 5 will be described. The examples described below are only a part of achievable examples of the light guide member 5 .

[0172] Table 1 below shows the parameters of Examples 1 to 6. Table 2 below shows the parameters of Comparative Examples 1 to 6. The parameters in Tables 1 and 2 are: Incident angle (propagation angle) θ i [°], extraction angle (angle at which the second image light L12 is emitted from the main body 50 ) θo [°], -1st order propagation angle (3rd angle) θ p [°], the diffraction spacing d [μm] of the diffraction structure of the emission expansion area 53, the thickness of the light guide component 5 (the thickness of the main body 50) T [μm], the refractive index of the light guide component 5 (the refractive index of the main body 50) n, the central wavelength λ [μm] of the image light L1, the line width Δλ [μm] of the image light L1, the number of round trips m1 of the first image light L11 in the emission expansion area 53 when it is incident on the overlapping portion 53a, and the number of round trips m2 of the third image light L13 in the emission expansion area 53 when it is incident on the overlapping portion 53a.

[0173] [Table 1]

[0174]

[0175] [Table 2]

[0176]

[0177] Table 3 below shows the coherence length Lc [μm] of the image light L1 in Examples 1 to 6 and the optical path length difference Ld between the first image light L11 and the third image light L13 incident on the overlapping portion 53a. Table 4 below shows the coherence length Lc [μm] of the image light L1 in Comparative Examples 1 to 6 and the optical path length difference Ld between the first image light L11 and the third image light L13 incident on the overlapping portion 53a.

[0178] [Table 3]

[0179]

[0180] [Table 4]

[0181]

[0182] As described above, Examples 1 to 6 satisfy Formula (2) according to Table 3. On the other hand, Comparative Examples 1 to 6 do not satisfy Formula (2) according to Table 4. Therefore, in Comparative Examples 1 to 6, the image quality of the virtual image Iv may be degraded compared to Examples 1 to 6.

[0183] When comparing Example 1 with Comparative Example 1, the line width Δλ is changed from 0.0001 [μm] of Comparative Example 1 to 0.003 [μm] of Example 1. As an example, the light source used in display element 2 is changed from a 0.1nm single-mode laser to a 3.0nm multi-mode laser. When comparing Example 2 with Comparative Example 2, the thickness T is changed from 500 [μm] of Comparative Example 2 to 1000 [μm] of Example 2. When comparing Example 3 with Comparative Example 3, the diffraction spacing d is changed from 2.337 [μm] of Comparative Example 3 to 1.817 [μm] of Example 3, and the refractive index is changed from 1.4 of Comparative Example 3 to 1.8 of Example 3. In Example 3, the propagation angle θ can be maintained. i , and satisfies formula (2). When comparing Example 4 with Comparative Example 4, the center wavelength λ is changed from 0.75 [μm] of Comparative Example 4 to 0.66 [μm] of Example 4. In Example 4, although the color of the image light L1 is changed, the degradation of the image quality caused by interference can be reduced. When comparing Example 5 with Comparative Example 5, the number of round trips m1 is changed from 2 of Comparative Example 5 to 3 of Example 5. In Example 5, by adjusting the number of round trips of the first image light L11 at the overlapping portion 53a, formula (2) can be satisfied, thereby reducing the degradation of the image quality caused by interference. When comparing Example 6 with Comparative Example 6, the thickness T is changed from 100 [μm] of Comparative Example 6 to 1000 [μm] of Example 6. In Example 6, compared with Comparative Example 6, the thickness T of the main body 50 can be set to 10 times, which can solve various problems such as the increase in the difficulty of material processing of the light guide member 5, the decrease in the strength of the light guide member 5, and the increase in the degree of influence on the vibration of the light guide member 5.

[0184] [1.3, Effects, etc.]

[0185] The optical system 3 described above includes a light guide member 5 that guides the image light L1 that forms an image output from the display element 2 to the visual field Ac of the user D as an optical image (virtual image Iv). The light guide member 5 includes: a plate-shaped main body 50; an incident area 51 formed in the main body 50, which allows the image light L1 to be incident on the main body 50 so that the image light L1 propagates in the main body 50; and an output expansion area 53 formed in the main body 50, which has a diffraction structure that splits the image light L1B that propagates in a first propagation direction that intersects the thickness direction of the main body 50 into a plurality of image lights L2 that propagate in a second propagation direction that intersects the first propagation direction, and emits the image light L2 from the main body 50. The emission expansion region 53 causes the image light L1B, L11, and L13 incident on the emission expansion region 53 and propagating in the first propagation direction to be branched into the first image light L11, the second image light L12, and the third image light L13 in a given plane P1 including the first propagation direction and the second propagation direction. The first image light L11 is emitted from the emission expansion region 53 at a first angle equal to the propagation angle of the image light L1B propagating from the incident region 51 to the emission expansion region 53 in the given plane P1, and propagates in the main body 50. The second image light L12 is emitted from the emission expansion region 53 at a second angle different from the first angle, and is emitted from the main body 50. The third image light L13 is emitted from the emission expansion region 53 at a third angle different from the first angle and the second angle, and propagates in the main body 50. The emission expansion area 53 includes an overlapping portion 53a where the first image light L11 and the third image light L13 are incident in a state of partially overlapping in a given plane P1. The optical path length difference between the first image light L11 and the third image light L13 incident on the overlapping portion 53a is longer than the coherence length of the image light L1. This structure can reduce the leakage filling of the pupil of the image light L1 in the field of view area Ac, and can reduce the size of the incident area 51.

[0186] In the optical system 3 , equations (1) and (2) are satisfied.

[0187] [Mathematical formula 23]

[0188]

[0189] [Mathematical formula 24]

[0190]

[0191] θ i is the propagation angle [°], θ o is the angle [°] at which the second image light L12 is emitted from the main body 50, θ pis the third angle, n is the refractive index of the main body 50, T is the thickness of the main body 50 [μm], m1 is the number of round trips of the first image light L11 in the emission expansion area 53 when incident on the overlapping portion 53a, m2 is the number of round trips of the third image light L13 in the emission expansion area 53 when incident on the overlapping portion 53a, λ is the central wavelength of the image light L1 [μm], and Δλ is the line width of the image light L1 [μm]. This structure can reduce the leakage filling of the pupil of the image light L1 in the field of view area Ac and can reduce the size of the incident area 51.

[0192] In the optical system 3, the propagation angle range is θ i0 -θ f2 Above and θ i0 +θ f1 In the following cases, formula (3) is satisfied.

[0193] [Mathematical formula 25]

[0194]

[0195] d is the diffraction pitch [μm] of the diffraction structure of the emission expansion region 53, n is the refractive index of the main body 50, and λ is the central wavelength [μm] of the image light L1. io θ is the propagation angle [°] of the central ray of the image light L1. f1 ,θ f2 is a positive value [°]. This structure can reduce the leak filling of the pupil of the image light L1 in the field of view area Ac, and can reduce the size of the incident area 51.

[0196] In the optical system 3, the portion where the image light L1B is branched into the first image light L11, the second image light L12, and the third image light L13 in the emission expansion area 53 is included in the optical path of the image light L1 from the incident area 51 to the emission expansion area 53, at the end of the emission expansion area 53 on the incident area 51 side. This structure can reduce the leakage filling of the pupil of the image light L1 in the field of view area Ac, and can reduce the size of the incident area 51.

[0197] In the optical system 3, the emission expansion area 53 branches the third image light L13 that has traveled back and forth an arbitrary number of times in the emission expansion area 53 into the first image light L11, the second image light L12, and the third image light L13. This structure can reduce the leakage filling of the pupil of the image light L1 in the field of view area Ac and can reduce the size of the incident area 51.

[0198] In the optical system 3, the irradiation area A10 of the image light L1 in the incident area 51 has a first dimension a1 in the first propagation direction and a second dimension a2 in a direction orthogonal to the thickness direction of the main body 50 and the first propagation direction, and the first dimension a1 is smaller than the second dimension a2. This structure can reduce the leakage filling of the pupil of the image light L1 in the field of view area Ac, and can reduce the size of the incident area 51.

[0199] In the optical system 3, the light guide member 5 further includes an auxiliary expansion region 52 formed in the main body 50 and having a diffractive structure that splits the image light L1A propagating in a given direction in the main body 50 through the incident region 51 into a plurality of image lights L1B propagating in a first propagation direction in a given direction and forwards the image lights to the exit expansion region 53. This structure enables the pupil to be expanded in a plurality of different directions.

[0200] In the optical system 3, the given direction corresponds to the horizontal direction of the viewing area Ac, and the first propagation direction corresponds to the vertical direction of the viewing area Ac. This configuration enables expansion of the pupil in the horizontal and vertical directions of the viewing area Ac.

[0201] In the optical system 3 , the light guide member 5 is positioned so that the image light L2 emitted from the main body 50 is reflected by the light-transmitting member (windshield 101 ) and guided to the visual field area Ac as an optical image (virtual image Iv). This structure can be used as a head-up display.

[0202] In the optical system 3, the main body 50 has a first surface 50a and a second surface 50b in the thickness direction. The incident region 51 allows the image light L1 incident on the first surface 50a of the main body 50 from the first oblique direction inclined relative to the normal line of the first surface 50a of the main body 50 to enter the main body 50 so that the image light L1 propagates in the main body 50. The emission expansion region 53 allows a plurality of image lights L1C propagating along the second propagation direction to be emitted from the second surface 50b of the main body 50 along the second oblique direction inclined relative to the normal line of the second surface 50b of the main body 50. This structure can reduce the leakage filling of the pupil of the image light L1 in the field of view area Ac, and can reduce the size of the incident region 51.

[0203] The first oblique direction and the second oblique direction are parallel to each other in the optical system 3. This structure can reduce the leakage filling of the pupil of the image light L1 in the field of view area Ac, and can reduce the size of the incident area 51.

[0204] In the optical system 3, the diffractive structure of the emission expansion region 53 is a volume hologram element located inside the main body 50. This structure can easily increase the size of the emission expansion region 53.

[0205] The optical system 3 further includes a projection optical system 6 that converts the image light L1 into substantially collimated light and causes the collimated light to enter the incident area 51 of the light guide member 5. This configuration can further improve the utilization efficiency of the image light L1 from the display element 2.

[0206] The image display device 1 described above includes the optical system 3 and the display element 2. This structure can reduce the leakage filling of the pupil of the image light L1 in the field of view area Ac, and can reduce the size of the incident area 51.

[0207] [2. Modifications]

[0208] The embodiments of the present disclosure are not limited to the above embodiments. As long as the subject of the present disclosure can be achieved, the above embodiments can be variously modified according to the design, etc. The following lists the modified examples of the above embodiments. The modified examples described below can be appropriately combined and applied.

[0209] In a modified example, the diffraction structure of the emission expansion region 53 is not limited to a volume hologram element (holographic diffraction grating), but may also be a surface relief type diffraction grating. The surface relief type diffraction grating may be a reflective type. The surface relief type diffraction grating is not limited to the same material as the light guide component 5, but may also be formed from a material different therefrom. For example, the material of the light guide component 5 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 nanoimprint technology. In addition, in the case where the diffraction structure of the emission expansion region 53 is a surface relief type diffraction grating, the refractive index of the emission expansion region 53 is the refractive index of the material forming the surface relief type diffraction grating.

[0210] In a modified example, the diffraction structure of the incident region 51 and the auxiliary expansion region 52 is not limited to a volume hologram element (holographic diffraction grating), and may be a surface relief type diffraction grating. In a modified example, the incident region 51 and the auxiliary expansion region 52 may have a half mirror.

[0211] In a variation, the propagation angle θ i The angle θ at which the second image light L12 is emitted from the main body 50 is greater than or equal to 42° and less than or equal to 50°. o is greater than 25° and less than 60°. The diffraction spacing d of the diffraction structure of the emission expansion area 53 is greater than 3.02×λ / n and less than 7.71×λ / n. λ is the central wavelength of the image light L1. n is the refractive index of the main body 50. This structure can reduce the leakage filling of the pupil of the image light L1 in the field of view area Ac, and can reduce the size of the incident area 51. In particular, when used as a head-up display, the utilization efficiency of the image light L1 from the display element 2 can be improved.

[0212] In a modified example, the light guide member 5 may not necessarily be positioned so that the image light L2 emitted from the main body 50 is reflected by the light-transmitting member (windshield 101) and guided to the visual field area Ac as an optical image (virtual image Iv). For example, the light guide member 5 may be positioned so as to be arranged in a straight line with the visual field area Ac. That is, the optical path from the light guide member 5 to the visual field area Ac may be a straight line.

[0213] In a modified example, the projection optical system 6 may not be a single optical element, but may include a first optical element and a second optical element as a plurality of optical elements. The first optical element is, for example, a cemented lens combining a negative meniscus lens and a biconvex lens, and the second optical element is a cemented lens combining a positive meniscus lens and a negative meniscus lens. In addition, the optical system 3 may not include the projection optical system 6.

[0214] In a modified example, the projection optical system 6 and the incident area 51 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 6 to the incident area 51 is not necessarily a straight line. For example, the image light L1 from the projection optical system 6 may be reflected by a reflector so as to be incident on the incident area 51. In this case, the optical path of the image light L1 from the projection optical system 6 to the incident area 51 is not a straight line, but is, for example, an L-shaped.

[0215] In a modified example, the image display device 1 may include a plurality of light guide members 5 corresponding to the wavelengths of light included in the image light L1. This makes it possible to provide a color image to the user.

[0216] In a modified example, the image display device 1 is not limited to a head-up display used in a car, and can be applied to a mobile object other than a car, such as a motorcycle, a train, an airplane, a construction machine, and a ship. Furthermore, the image display device 1 is not limited to being used in a mobile object, and can be used in an entertainment facility, or as a wearable terminal such as a head mounted display (HMD), a medical device, or a stationary device.

[0217] In addition, in each of the above-mentioned embodiments, a display element 2 and an optical system 3 for visually confirming a virtual image Iv as an example of an optical image are described. In the present embodiment, the display element 2 is configured so that the optical image to be visually confirmed is not limited to the virtual image Iv, and may be, for example, a real image. For example, the display element 2 may also be configured so that a real image is formed between a light-transmitting member such as a windshield 101 and a user D through the same pupil dilation type optical system 3 as described above. Such display of a real image is useful, for example, for entertainment purposes. In the case of visually confirming such a real image as an optical image, the influence of polarization in the light-guiding member 5 is considered with respect to uneven brightness, as in the case of the above-mentioned virtual image Iv. According to the display element 2 and the optical system 3 disclosed in the present invention, uneven brightness is suppressed by controlling the polarization state, as in the above-mentioned embodiments, and changes in the image quality of the real image can be suppressed.

[0218] [3. Method]

[0219] As is clear from the above-described embodiment and modified examples, the present disclosure includes the following aspects. In the following, only for the purpose of clarifying the correspondence with the embodiment, the reference numerals are indicated with parentheses.

[0220] The first mode is an optical system (3) comprising: a light guide member (5) for guiding image light (L1) forming an image output from a display element (2) to a field of view (Ac) of a user (D) as an optical image (virtual image Iv). The light guide member (5) comprises: a plate-shaped main body (50); an incident area (51) formed in the main body (50) for causing the image light (L1) to enter the main body (50) so that the image light (L1) propagates in the main body (50); and an emission expansion area (53) formed in the main body (50) and having a diffraction structure for splitting image light (L1B) propagating in a first propagation direction intersecting with a thickness direction of the main body (50) in the first propagation direction into a plurality of image lights (L2) propagating in a second propagation direction intersecting with the first propagation direction and emitting the image light from the main body (50). The emission expansion region (53) causes the image light (L1B, L11, L13) incident on the emission expansion region (53) and propagating along the first propagation direction to branch into a first image light (L11), a second image light (L12), and a third image light (L13) in a given plane (P1) including the first propagation direction and the second propagation direction. The first image light (L11) is emitted from the emission expansion region (53) at a first angle equal to the propagation angle of the image light (L1B) propagating from the incident region (51) to the emission expansion region (53) in the given plane (P1), and propagates in the main body (50). The second image light (L12) is emitted from the emission expansion region (53) at a second angle different from the first angle, and is emitted from the main body (50). The third image light (L13) is emitted from the emission expansion area (53) at a third angle different from the first angle and the second angle, and propagates in the main body (50). The emission expansion area (53) includes an overlapping portion (53a) where the first image light (L11) and the third image light (L13) are incident in a state of partially overlapping in the given plane (P1). The optical path length difference between the first image light (L11) and the third image light (L13) incident on the overlapping portion (53a) is longer than the coherence length of the image light (L1). This method can improve the filling rate of the pupil of the image light (L1) in the field of view area (Ac) and can reduce the size of the incident area (51).

[0221] The second aspect is an optical system (3) based on the first aspect. In this aspect, equations (1) and (2) are satisfied.

[0222] [Mathematical formula 26]

[0223]

[0224] [Mathematical formula 27]

[0225]

[0226] θ i is the propagation angle [°], θ o is the angle [°] at which the second image light (L12) is emitted from the main body (50), θ p is the third angle, n is the refractive index of the main body (50), T is the thickness of the main body (50) [μm], m1 is the number of round trips of the first image light (L11) in the emission expansion area (53) when incident on the overlapping portion (53a), m2 is the number of round trips of the third image light (L13) in the emission expansion area (53) when incident on the overlapping portion (53a), λ is the central wavelength of the image light (L1) [μm], and Δλ is the line width of the image light (L1) [μm]. This method can improve the pupil filling rate of the image light (L1) in the field of view area (Ac) and reduce the size of the incident area (51).

[0227] The third aspect is an optical system (3) based on the first or second aspect. In this aspect, the range of the propagation angle is θ i0 -θ f2 Above and θ i0 +θ f1 In the following cases, formula (3) is satisfied.

[0228] [Mathematical formula 28]

[0229]

[0230] d is the diffraction pitch [μm] of the diffraction structure of the emission expansion region (53), n is the refractive index of the main body (50), and λ is the central wavelength [μm] of the image light (L1). io θ is the propagation angle [°] of the central ray of the image light (L1). f1 ,θ f2 is a positive value [°]. This method can increase the filling rate of the pupil of the image light (L1) in the field of view area (Ac) and can reduce the size of the incident area (51).

[0231] The fourth aspect is an optical system (3) based on any one of the first to third aspects. In this aspect, the portion of the light branching into the first image light (L11), the second image light (L12), and the third image light (L13) in the emission expansion area (53) is included in the optical path of the image light (L1) from the incident area (51) to the emission expansion area (53), at the end of the emission expansion area (53) on the side of the incident area (51). This aspect can improve the filling rate of the pupil of the image light (L1) in the field of view area (Ac), and can reduce the size of the incident area (51).

[0232] The fifth aspect is an optical system (3) based on the fourth aspect. In this aspect, the emission expansion region (53) branches the third image light (L13) that has traveled back and forth an arbitrary number of times in the emission expansion region (53) into the first image light (L11), the second image light (L12), and the third image light (L13). This aspect can improve the pupil filling rate of the image light (L1) in the field of view region (Ac) and can reduce the size of the incident region (51).

[0233] A sixth aspect is an optical system (3) based on any one of the first to fifth aspects. In this aspect, an irradiation area (A10) of the image light (L1) in the incident area (51) has a first dimension (a1) in the first propagation direction and a second dimension (a2) in a direction orthogonal to the thickness direction of the main body (50) and the first propagation direction, and the first dimension (a1) is smaller than the second dimension (a2). This aspect can improve the filling rate of the pupil of the image light (L1) in the field of view area (Ac) and can reduce the size of the incident area (51).

[0234] A seventh aspect is an optical system (3) according to any one of the first to sixth aspects. In this aspect, the light guide member (5) further comprises: an auxiliary expansion region (52) formed in the main body (50) and having a diffraction structure that causes the image light (L1A) propagating in a given direction in the main body (50) through the incident region (51) to be split in the given direction into a plurality of image lights (L1B) propagating in the first propagation direction and heading to the exit expansion region (53). This aspect can dilate the pupil in a plurality of different directions.

[0235] The eighth aspect is an optical system (3) based on the seventh aspect. In this aspect, the given direction corresponds to the horizontal direction of the field of view (Ac), and the first propagation direction corresponds to the vertical direction of the field of view (Ac). This aspect can dilate the pupil in the horizontal direction and the vertical direction of the field of view (Ac).

[0236] A ninth aspect is an optical system (3) according to any one of the first to eighth aspects. In this aspect, the light guide member (5) is positioned so that the image light (L2) emitted from the main body (50) is reflected by the light-transmitting member (windshield 101) and guided to the visual field area (Ac) as the optical image (virtual image Iv). This aspect can be used as a head-up display.

[0237] The tenth aspect is an optical system (3) based on the ninth aspect. In this aspect, the main body (50) has a first surface (50a) and a second surface (50b) in the thickness direction. The incident area (51) allows the image light (L1) incident on the first surface (50a) of the main body (50) from a first oblique direction inclined relative to the normal line of the first surface (50a) of the main body (50) to enter the main body (50), so that the image light (L1) propagates in the main body (50). The emission expansion area (53) causes the plurality of image lights (L1C) propagating along the second propagation direction to be emitted from the second surface (50b) of the main body (50) along the second oblique direction inclined relative to the normal line of the second surface (50b) of the main body (50). This aspect can improve the pupil filling rate of the image light (L1) in the field of view area (Ac) and can reduce the size of the incident area (51).

[0238] The eleventh embodiment is an optical system (3) based on the tenth embodiment. In this embodiment, the first oblique direction and the second oblique direction are parallel to each other. This embodiment can improve the pupil filling rate of the image light (L1) in the field of view area (Ac) and can reduce the size of the incident area (51).

[0239] The twelfth method is an optical system (3) based on any one of the ninth to eleventh methods. In this method, the propagation angle is greater than 42° and less than 50°. The angle at which the second image light (L12) is emitted from the main body (50) is greater than 25° and less than 60°. The diffraction spacing of the diffraction structure of the emission expansion area (53) is greater than 3.02×λ / n and less than 7.71×λ / n. λ is the central wavelength of the image light (L1). n is the refractive index of the main body (50). This method can increase the filling rate of the pupil of the image light (L1) in the field of view area (Ac) and can reduce the size of the incident area (51).

[0240] A thirteenth aspect is an optical system (3) according to any one of the first to twelfth aspects. In this aspect, the diffraction structure of the emission expansion region (53) is a volume hologram element located inside the main body (50). This aspect can easily increase the size of the emission expansion region (53).

[0241] A 14th aspect is an optical system (3) according to any one of the 1st to 13th aspects. In this aspect, the optical system (3) further comprises: a projection optical system (6) for causing the image light (L1) to be substantially collimated light and to be incident on the incident area (51) of the light guide member (5). This aspect can further improve the utilization efficiency of the image light (L1) from the display element (2).

[0242] A fifteenth aspect is an image display device (1) comprising an optical system (3) according to any one of the first to fourteenth aspects and the display element (2). This aspect can increase the pupil filling rate of the image light (L1) in the field of view region (Ac) and can reduce the size of the incident region (51).

[0243] The above-mentioned second to fourteenth aspects are not essential.

[0244] As described above, an implementation method is described as an illustration of the technology in the present disclosure. For this purpose, drawings and detailed descriptions are provided. Therefore, the constituent elements recorded in the drawings and detailed descriptions include not only the constituent elements necessary for solving the problem, but also constituent elements that are not necessary for solving the problem in order to illustrate the above-mentioned technology. Therefore, it should not be directly determined that these non-essential constituent elements are necessary based on the fact that they are recorded in the drawings and detailed descriptions. In addition, the above-mentioned implementation methods are used to illustrate the technology in the present disclosure, so various changes, substitutions, additions, omissions, etc. can be made within the scope of the claims or their equivalents.

[0245] Industrial Applicability

[0246] 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 to a user's visual field as an optical image, and an image display device including the optical system.

[0247] Description of Reference Numerals

[0248] 1 Image display device

[0249] 2 Display components

[0250] 3 Optical system

[0251] 5 Light guide components

[0252] 50 Main body

[0253] 50a Side 1

[0254] 50b Side 2

[0255] 51 Incident area

[0256] 52 Auxiliary expansion area

[0257] 53 Exit expansion area

[0258] 6 Projection optical system

[0259] 100 Mobile

[0260] 101 Windshield (light-transmitting component)

[0261] Ac visual field

[0262] D User

[0263] IV virtual image (optical image)

[0264] L1, L1A, L1B, L1C, L2 Image light

[0265] L11 1st image light

[0266] L12 2nd image light

[0267] L13 3rd image light

[0268] P1 given plane.

Claims

1. An optical system comprising a light guide member for guiding image light forming an image output from a display element to a visual field of a user as an optical image, The light guide member comprises: plate-like main body; an incident area formed in the main body portion to allow the image light to be incident into the main body portion so that the image light propagates within the main body portion; and an emission expansion region formed in the main body and having a diffraction structure that splits image light propagating in a first propagation direction intersecting with a thickness direction of the main body into a plurality of image lights propagating in a second propagation direction intersecting with the first propagation direction, and emits the image light from the main body; The emission expansion region causes the image light incident on the emission expansion region and propagating along the first propagation direction to be branched into a first image light, a second image light, and a third image light within a given plane including the first propagation direction and the second propagation direction. The first image light is emitted from the emission expansion area at a first angle equal to a propagation angle of the image light propagating from the incident area to the emission expansion area in the given plane, and propagates in the main body. The second image light is emitted from the emission expansion region at a second angle different from the first angle, and is emitted from the main body. The third image light is emitted from the emission expansion region at a third angle different from the first angle and the second angle, and propagates in the main body. The emission expansion region includes an overlapping portion where the first image light and the third image light are incident in a state of partially overlapping in the given plane. A difference in optical path length between the first image light and the third image light incident on the overlapping portion is longer than a coherence length of the image light.

2. The optical system according to claim 1, wherein: The optical system satisfies equations (1) and (2), [Mathematical formula 1] [Mathematical formula 2] θ i is the propagation angle [°], θ o is the angle [°] at which the second image light is emitted from the main body, θ p is the third angle, n is the refractive index of the main body, T is the thickness of the main body [μm], m1 is the number of round trips of the first image light within the emission expansion region when incident on the overlapping portion, m2 is the number of round trips of the third image light within the emission expansion region when incident on the overlapping portion, λ is the central wavelength of the image light [μm], Δλ is the line width [μm] of the image light.

3. The optical system according to claim 1 or 2, wherein: In the range of the propagation angle θ i0 -θ f2 Above and θ i0 +θ f1 In the following cases, the optical system satisfies equation (3), [Mathematical formula 3] d is the diffraction pitch [μm] of the diffraction structure of the emission expansion region, n is the refractive index of the main body, λ is the central wavelength of the image light [μm], θ io is the propagation angle of the central ray of the image light [°], θ f1 and θ f2 is a positive value [°].

4. The optical system according to claim 1 or 2, wherein: The portion in the emission expansion region where the image light is branched into the first image light, the second image light, and the third image light is at least included in the optical path of the image light from the incident region to the emission expansion region, at an end portion of the emission expansion region on the incident region side.

5. The optical system according to claim 4, wherein: The emission expansion region branches the third image light having reciprocated an arbitrary number of times in the emission expansion region into the first image light, the second image light, and the third image light.

6. The optical system according to claim 1 or 2, wherein: The illumination area of ​​the image light in the incident area has: a first dimension in the first propagation direction; and a second dimension in a direction orthogonal to the thickness direction of the main body and the first propagation direction, The first size is smaller than the second size.

7. The optical system according to claim 1 or 2, wherein: The optical system also includes: an auxiliary expansion area, which is formed in the main body and has a diffraction structure, which causes the image light that passes through the incident area and propagates along a given direction in the main body to be divided into a plurality of image lights that propagate along the first propagation direction in the given direction and go to the exit expansion area.

8. The optical system according to claim 7, wherein: The given direction corresponds to the horizontal direction of the field of view, The first propagation direction corresponds to a vertical direction of the viewing area.

9. The optical system according to claim 1 or 2, wherein: The light guide member is positioned so that the image light emitted from the main body is reflected by the light transmissive member and guided to the field of view area as the optical image.

10. The optical system according to claim 9, wherein: The main body has a first surface and a second surface in the thickness direction. The incident region allows the image light incident on the first surface of the main body from a first oblique direction inclined relative to the normal line of the first surface of the main body to enter the main body so that the image light propagates in the main body. The emission expansion region causes the plurality of image lights propagating along the second propagation direction to be emitted from the second surface of the main body portion in a second inclined direction inclined with respect to a normal line of the second surface of the main body portion.

11. The optical system according to claim 10, wherein: The first inclined direction and the second inclined direction are parallel to each other.

12. The optical system according to claim 9, wherein: The propagation angle is greater than 42° and less than 50°, The angle at which the second image light is emitted from the main body is greater than or equal to 25° and less than or equal to 60°, The diffraction pitch of the diffraction structure of the emission expansion region is greater than or equal to 3.02×λ / n and less than or equal to 7.71×λ / n, λ is the central wavelength of the image light, n is the refractive index of the main body.

13. The optical system according to claim 1 or 2, wherein: The diffractive structure of the emission expansion region is a volume hologram element located inside the main body.

14. The optical system according to claim 1 or 2, wherein: The optical system further includes a projection optical system that converts the image light into substantially collimated light and causes the collimated light to enter the incident area of ​​the light guide member.

15. An image display device comprising: The optical system of claim 1 or 2; and The display element.

Images