Optical system and image display device

Abstract

Provided are an optical system and an image display device capable of improving the utilization efficiency of image light from a display element. A light guide member (5) of an optical system is provided with: an emission expansion region (53) having a diffraction structure for dividing, in the first propagation direction, image light (L1B) that is incident into a main body section (50) from an incidence region (51) and that propagates in the first propagation direction intersecting the thickness direction of the main body section (50) into a plurality of image light (L1C) that propagate in the second propagation direction intersecting the first propagation direction; the light is emitted from the light guide member (5). At least a part of the emission expansion region (53) is configured such that the refractive indexes of the media on the incidence side and the emission side of the image light with respect to the emission expansion region (53) are equal to each other. The emission angle [theta] out of the image light (LIC) emitted at the highest diffraction efficiency from the emission expansion region (53) in a given plane (P1) including the normal (N) of the emission expansion region (53) is 15-45 degrees, and the incidence angle [theta] in of the image light (LIB) incident on the emission expansion region (53) in the given plane (P1) is 14 degrees or more larger than the emission angle [theta] out.

Description

Technical Field

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

[0002] In the past, a vehicle information projection system that uses a head-up display device to perform augmented reality (AR) display has been disclosed. The head-up display device projects light representing a virtual image (image light from a display element) onto the windshield of the vehicle, for example, so that the driver can visually recognize the virtual image together with the real scene outside the vehicle.

[0003] Patent Document 1 describes a display system for displaying a virtual image, which describes that a light beam emitted from the inside of a waveguide (light guide) is diffracted by a diffraction element to change the traveling direction of the light beam.

[0004] Prior Art Literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application No. 2018-506068 Summary of the invention

[0007] Problems to be solved by the invention

[0008] In the display system described in Patent Document 1, it is desired to improve the utilization efficiency of image light from a display element.

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

[0010] Means for solving problems

[0011] An optical system according to one embodiment of the present disclosure includes: a light guide member that guides image light output from a display element to form an image as an optical image to a user's field of view. The light guide member includes: a plate-shaped main body; an incident area formed in the main body that allows the image light to be incident on the main body so that the image light propagates in the main body; and an emission expansion area formed in the main body that has a diffraction structure that splits the image light propagating in a first propagation direction intersecting the thickness direction of the main body into a plurality of image lights propagating in a second propagation direction intersecting the first propagation direction, and emits the image light from the light guide member. When the refractive indices of a medium on the incident side of image light relative to the exit expansion area and a medium on the exit side of image light relative to the exit expansion area are equal to each other in at least a portion of the exit expansion area, an exit angle θ_out of image light emitted from the exit expansion area with the highest diffraction efficiency within a given plane including the normal to the exit expansion area is greater than 15° and less than 45°, and an incident angle θ_in of image light incident on the exit expansion area within the given plane is greater than the exit angle θ_out by more than 14°.

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

[0013] Effects of the Invention

[0014] The aspect of the present disclosure can improve the utilization efficiency of image light from a display element. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic diagram of a configuration example of a moving object including an image display device according to an embodiment.

[0016] 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.

[0017] Figure 3 yes Figure 1 A three-dimensional diagram of a structural example of a light guide component of an image display device.

[0018] Figure 4 yes Figure 3 A schematic top view of a light-guiding component.

[0019] Figure 5 This is a schematic diagram of a volume hologram element.

[0020] Figure 6 is a graph showing an example of the relationship between the incident angle and the emission angle.

[0021] Figure 7 yes Figure 3An illustration of the diffraction effect of the output expansion area of ​​the light-guiding component on the image light.

[0022] Figure 8 It is an explanatory diagram of the diffraction effect of image light by the emission expansion region of the light guide member of the comparative example.

[0023] Fig. 9 : is a graph showing an example of the relationship between the incident angle of image light into the emission expansion region and the ratio of -1st order diffracted light.

[0024] Fig.10 is a graph showing an example of the relationship between the diffraction pitch and the diffraction efficiency.

[0025] Fig.11 yes Figure 3 An explanatory diagram of the incident angle and the emission angle of the image light in the XZ plane of the light guide component.

[0026] Fig.12 yes Figure 3 An illustration of the incident angle and the outgoing angle of the image light in the YZ plane of the light guide component.

[0027] Fig.13 This is a schematic diagram for explaining a surface relief type diffraction grating. DETAILED DESCRIPTION

[0028] 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.

[0029] 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.

[0030] 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.

[0031] [1. Implementation Method]

[0032] [1.1, Structure]

[0033] 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 .

[0034] 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.

[0035] Figure 1 The image display device 1 includes a display element 2 , an optical system 3 , and a control device 4 .

[0036] The display element 2 outputs image light L1 that forms an image in order to display an image (video). Figure 1 For the sake of simplicity, the image light L1 is drawn as directional light, 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. As examples of the display element 2, there can be listed known displays such as liquid crystal displays, organic EL displays, scanning MEMS mirrors, LCOS (Liquid Crystal On Silicon), DMD (Digital Mirror Device), and micro LEDs. The image based on the image light L1 is used to visually display various information such as road guidance display, distance to the vehicle ahead, battery level of the vehicle, current vehicle speed, etc.

[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 confirmation area Ac is defined by a rectangular plane. As long as it is within the visual field Ac, 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-axis orthogonal coordinates of XYZ are recorded 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 3The 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 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 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 along a given direction (positive direction of the X axis) orthogonal 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. That is, the incident area 51 changes the traveling direction of the image light L1 incident on the incident area 51 so that it propagates in a given direction in the main body 50 as image light L1A. In the present embodiment, the incident area 51 is used for coupling (Coupling) between the display element 2 and the light guide component 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 component 5 under the condition of total reflection.

[0046] The incident region 51 is formed of a diffractive structure (periodic structure) having a diffractive effect on the image light L1. The diffractive structure of the incident region 51 is, for example, a volume hologram element (holographic diffraction grating). The incident region 51 is formed, for example, inside the main body 50.

[0047] Figure 5 This is a schematic diagram of a volume hologram element. The volume hologram element produces diffraction through periodic modulation of the refractive index. Figure 5 In the figure, the direction of the Z1 axis is the thickness direction of the volume hologram element. The directions of the X1 axis and the Y1 axis are orthogonal to the direction of the Z1 axis and are orthogonal to each other. The direction of the X1 axis is the direction in which the refractive index of the volume hologram element does not change. The direction of the Y1 axis is the direction in which the refractive index of the volume hologram element changes periodically. Figure 5 Gp represents the diffraction period (diffraction pitch) [μm] of the volume hologram element. The diffraction period of the volume hologram element represents the period of change in 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.

[0048] exist Figure 4 , Gp1 represents the diffraction period of the volume hologram element of the incident region 51, and X11, Y11 and Z11 represent the X1, Y1 and Z1 axes of the volume hologram element of the incident region 51, respectively. The direction of the X11 axis (the direction in which the refractive index does not change) of the volume hologram element of the incident region 51 is in a plane orthogonal to the thickness direction of the main body 50 (in the XY plane), and intersects the direction of the Y axis at an angle Ga1.

[0049] 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.

[0050] 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.

[0051] 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. Figure 4 , Gp2 represents the diffraction period of the volume hologram element of the auxiliary extension region 52, and X12, Y12, and Z12 represent the X1, Y1, and Z1 axes of the volume hologram element of the auxiliary extension region 52, respectively. The direction of the X1 axis (the direction in which the refractive index does not change) of the volume hologram element of the auxiliary extension region 52 intersects the direction of the Y axis at an angle Ga2 in a plane orthogonal to the thickness direction of the main body 50 (in the XY plane).

[0052] 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 4 In 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).

[0053] 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 in shape.

[0054] 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). Figure 4 In FIG. 5 , the diffraction period of the volume hologram element of the emission expansion region 53 is represented by Gp3, and the X13 axis, the Y13 axis, and the Z1 axis of the volume hologram element of the emission expansion region 53 are represented by the X13 axis, the Y1 axis, and the Z1 axis, respectively. The direction of the X1 axis (the direction in which the refractive index does not change) of the volume hologram element of the emission expansion region 53 intersects the direction of the Y axis at an angle Ga3 in a plane orthogonal to the thickness direction of the main body 50 (in the XY plane).

[0055] 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 3 In 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.

[0056] In this way, the auxiliary expansion area 52 and the exit 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, thereby replicating the pupil of the image light L1. In the present embodiment, the auxiliary expansion area 52 and the exit 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 area Ac, thereby replicating the pupil of the image light L1. The plurality of image lights L2 arriving at the field of view area Ac may be parallel to each other. The expression "the plurality of image lights L2 are parallel to each other" is not limited to the plurality of image lights L2 being parallel to each other in a strict sense, but includes the case where the plurality of image lights L2 are substantially parallel to each other. Even if the plurality of image lights L2 are not parallel to each other in a strict sense, 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 parallel in optical design. Since the plurality of image lights L2 are parallel to each other, the uniformity of the arrangement of the pupil of the image light in the field of view region Ac can be improved, thereby reducing the leakage filling of the pupil of the image light in the field of view region Ac. Figure 2 As 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.

[0057] 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 and makes it incident on the incident area 51. The projection optical system 6 is, for example, a biconvex lens.

[0058] The control device 4 can be implemented by semiconductor elements and the like. The control device 4 can be composed of, for example, a microcomputer, a CPU, an MPU, a GPU, a DSP, an FPGA or an ASIC. The control device 4 realizes 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 realize the functions of the control device 4. The storage device 4a is realized, 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 as an optical image are stored in the storage device 4a. The control device 4 determines the virtual image Iv to be displayed based on the vehicle-related information obtained from the outside. The control device 4 reads the image data of the determined virtual image Iv from the storage device 4a and outputs it to the display element 2.

[0059] In the image display device 1 described above, the light guiding member 5 is configured so that, when the refractive indices of a medium on the incident side of the image light relative to the exit expansion area 53 and a medium on the exit side of the image light relative to the exit expansion area 53 are equal to each other, the relationship that θ_out is greater than 15° and less than 45° and θ_in is greater than θ_out by more than 14° is satisfied.

[0060] like Figure 3 As shown, θ_in is the incident angle of the image light L1B incident on the exit expansion area 53 within a given plane P1 including the normal line N1 of the exit expansion area 53. θ_out is the exit angle of the image light L1C emitted from the exit expansion area 53 with the highest diffraction efficiency within a given plane P1 including the normal line N1 of the exit expansion area 53.

[0061] This can reduce the generation of unnecessary diffracted light (hereinafter, also simply referred to as unnecessary light) in the emission expansion region 53 . This can improve the utilization efficiency of the image light L1 from the display element 2 .

[0062] In particular, in the present embodiment, the light guide member 5 is configured to satisfy the following formula (1).

[0063] [Mathematical formula 1]

[0064]

[0065] In the present embodiment, when the refractive index of the medium on the incident side of the image light with respect to the emission expansion region 53 and the refractive index of the medium on the emission side of the image light with respect to the emission expansion region 53 are equal to each other, at least a portion of the emission expansion region 53 satisfies the formula (1), thereby reducing the generation of useless diffracted light (hereinafter also referred to as useless light) in the emission expansion region 53. As a result, the utilization efficiency of the image light L1 from the display element 2 can be improved.

[0066] Here, at least a portion of the emission expansion region 53 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, or in 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, Figure 4 In 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 on the negative side of the X-axis of the exit expansion region 53, but the end on the negative side of the Y-axis. In the present embodiment, the end of the exit expansion region 53 on the incident region 51 side may be a region occupying 1 / 4 of the exit expansion region 53 in the first propagation direction from one end 53a 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 reducing the generation of useless light in the portion where the amount of image light L1B incident on the emission expansion region 53 is large, the utilization efficiency of the image light L1 from the display element 2 can be effectively improved. Of course, the light guide member 5 can be configured so that the entire emission expansion region 53 satisfies the formula (1) when the refractive index of the medium on the incident side of the image light relative to the emission expansion region 53 and the refractive index of the medium on the emission side of the image light relative to the emission expansion region 53 are equal.

[0067] The lower limit of the incident angle θ_in satisfying the formula (1) is shown in Table 1. In Table 1, the incident angle θ_in is a value rounded off to the nearest decimal point.

[0068] [Table 1]

[0069]

[0070] Figure 6Graphs showing an example of the relationship between the incident angle θ_in and the outgoing angle θ_out. R1 shows the relationship in Table 1, and R2 shows the relationship of θ_in=θ_out only for reference.

[0071] At least when θ_out is 15° or more and 45° or less, R1 can be approximated as a straight line. Based on this, in this embodiment, the light guide member 5 is configured to satisfy the following equation (2). In the following equation (2), the incident angle θ_in is a value rounded off to the nearest decimal point.

[0072] [Mathematical formula 2]

[0073]

[0074] In the present embodiment, when at least a portion of the emission expansion region 53 is set such that the refractive index of the medium on the incident side of the image light with respect to the emission expansion region 53 and the refractive index of the medium on the exit side of the image light with respect to the emission expansion region 53 are equal to each other, by satisfying equation (2), the generation of useless light in the emission expansion region 53 can be reduced. Thus, the utilization efficiency of the image light L1 from the display element 2 can be improved.

[0075] Next, refer to Figure 7 as well as Figure 8 , the above formula (1) is explained. Figure 7 It is an explanatory diagram of the diffraction effect of the emission expansion region 53 of the light guide member 5 on the image light L1B. Figure 8 1 is an explanatory diagram of the diffraction effect of the emission expansion area 53 on the image light of the light guide member 500 of a comparative example. The diffraction by the emission expansion area 53 is expressed by the following formula (3).

[0076] [Mathematical formula 3]

[0077]

[0078] In formula (3), m is the diffraction order. d is the diffraction pitch (diffraction period). λ is the wavelength of the image light L1B. θm is the emission angle of the image light (m-order diffracted light) diffracted in the mth order and emitted from the emission expansion area 53 in a given plane P1 including the normal line N1 of the emission expansion area 53.

[0079] In formula (3), n_in is the refractive index of the medium on the incident side of the image light relative to the emission expansion area 53. n_out is the refractive index of the medium on the emission side of the image light relative to the emission expansion area 53. In the present embodiment, the medium on the incident side of the image light relative to the emission expansion area 53 and the medium on the emission side of the image light relative to the emission expansion area 53 are both the main body 50 of the light guide member 5. The refractive index n_in and the refractive index n_out are equal. Therefore, if the refractive index of the main body 50 of the light guide member 5 is set to n0, the following formula (4) can be obtained according to the above formula (3).

[0080] [Formula 4]

[0081]

[0082] exist Figure 8 In the embodiment, image light L1C, L1D, and L1E traveling in different directions can be obtained according to image light L1B through the exit expansion area 53. Here, image light L1C is 1st order diffraction light, image light L1D is -1st order diffraction light, and image light L1E is 2nd order diffraction light. Image light L1B on the exit side relative to the exit expansion area 53 is 0th order diffraction light.

[0083] The image light L1C is image light emitted from the emission expansion region 53 with the highest diffraction efficiency. The image light L1C is first-order diffracted light, so m=1, and the following equation (5) holds.

[0084] [Formula 5]

[0085]

[0086] The image light L1D is useless light. Since the image light L1D is -1st order diffracted light, m=-1, and the following equation (6) holds.

[0087] [Mathematical formula 6]

[0088]

[0089] like Figure 7 As shown in FIG. 1 , by eliminating the image light L1D, the amount of the image light L1C increases. As a result, it is expected that the utilization efficiency of the image light L1 from the display element 2 will be improved. The condition for the absence of the image light L1D is that the image light L1D does not exist on the emission side relative to the emission expansion area 53, which is consistent with the absence of θ -1 Based on the above, the condition that the image light L1D does not exist is given by the following equation (7).

[0090] [Mathematical formula 7]

[0091]

[0092] According to equation (6) and equation (7), the following equation (8) can be obtained.

[0093] [Mathematical formula 8]

[0094]

[0095] According to equation (5) and equation (8), the following equation (9) can be obtained.

[0096] [Mathematical formula 9]

[0097]

[0098] Since the image light L1C is image light emitted from the emission expansion region 53 with the highest diffraction efficiency, by replacing θ1 with θ_out in the equation (9) and modifying the equation, the above equation (1) is obtained.

[0099] The term “when the refractive indexes of the medium on the incident side of the image light with respect to the exit expansion area 53 and the medium on the exit side of the image light with respect to the exit expansion area 53 are equal to each other” means, for example, that the exit angle sinθ_out is corrected in advance on the condition that the refractive indexes of the medium on the incident side of the image light with respect to the exit expansion area 53 and the medium on the exit side of the image light with respect to the exit expansion area 53 are equal to each other. For example, the exit angle sinθ_out when the refractive indexes of the medium on the incident side of the image light with respect to the exit expansion area 53 and the medium on the exit side of the image light with respect to the exit expansion area 53 are different from each other is set to sinθ_out1, and the exit angle sinθ_out when the refractive indexes of the medium on the incident side of the image light with respect to the exit expansion area 53 and the medium on the exit side of the image light with respect to the exit expansion area 53 are equal to each other is set to sinθ_out2. If the above-mentioned refractive indexes n_in and n_out are used, sinθ_out2=(n_out / n_in)×sinθ_out1. That is, in the formula (1), sinθ_out2 may be used as sinθ_out.

[0100] Figure 8 The light guide member 500 of the comparative example has Figure 3 The light guide member 5 of the comparative example has the same structure as the light guide member 5 of the comparative example, but unlike the light guide member 5, the emission expansion area 530 does not satisfy the above formula (1) in any part. Therefore, the image light L1D exists in the light guide member 500 of the comparative example. Due to the existence of the image light L1D, the light amount of the image light L1C is reduced, which may be a cause of the decrease in the utilization efficiency of the image light L1 from the display element 2.

[0101] Fig. 9: is a graph showing an example of the relationship between the incident angle (θ_in) of the image light L1B to the emission expansion area 53 and the proportion of the -1st order diffracted light (image light L1D). As an example, when the incident angle is 43°, the proportion of the 1st order diffracted light is 18%, the proportion of the -1st order diffracted light is 10%, and the proportion of the 2nd order diffracted light is 0.6%. As an example, when the incident angle is 51°, the proportion of the 1st order diffracted light is 22%, the proportion of the -1st order diffracted light is 0%, and the proportion of the 2nd order diffracted light is 0.2%. Therefore, by eliminating the -1st order diffracted light (image light L1D), the proportion of the 1st order diffracted light (image light L1C), that is, the amount of light, increases. As a result, it can be expected that the utilization efficiency of the image light L1 from the display element 2 will be improved.

[0102] The diffraction efficiency based on the diffraction structure of the emission expansion region 53 may vary depending on the diffraction pitch (diffraction period Gp3) and the polarization state of the image light. Fig.10 is a graph showing an example of the relationship between the diffraction pitch and the diffraction efficiency. Fig.10 Graph F1 shows a change in the maximum value of the diffraction efficiency due to the diffraction pitch when the polarization state of the image light is changed. Fig.10 The curve F2 shows the change of the minimum value of the diffraction efficiency caused by the diffraction pitch when the polarization state of the image light is changed. Fig.10 In FIG. 5 , the incident angle of the image light to the emission expansion region 53 is 45°, and the wavelength of the image light is 0.52 μm. Fig.10 In FIG. 5 , the diffraction structure of the emission expansion region 53 is a volume hologram element, in which the thickness is 5 μm, the refractive index is 1.505, and the refractive index modulation amount is 0.03.

[0103] according to Fig.10 , in the range of diffraction spacing of 1.4μm to 2.0μm, the maximum and minimum values ​​of the diffraction efficiency become larger. If the diffraction spacing is lower than about 0.45μm, the difference between the maximum and minimum values ​​of the diffraction efficiency increases sharply. The increase in the difference between the maximum and minimum values ​​of the diffraction efficiency leads to an increase in the change in the diffraction efficiency during the propagation of the image light in the exit expansion area 53, which becomes a reason for the decrease in the image quality of the virtual image Iv. This is because, during pupil expansion, any image light is accompanied by a change in polarization state through the diffraction structure. When the diffraction spacing is too large, the maximum and minimum values ​​of the diffraction efficiency also become smaller. Fig.10 In the case where the diffraction pitch is about 3.5 μm, the maximum and minimum values ​​of the diffraction efficiency are about half of the peak value (the maximum and minimum values ​​of the diffraction efficiency in the range of the diffraction pitch of 1.4 μm to 2.0 μm).

[0104] The diffraction structure of the emission expansion region 53 is changed, and at the same time Fig.10 The change of the maximum value and the minimum value of the diffraction efficiency caused by the diffraction pitch when the polarization state of the image light is changed as shown in the figure was simulated, and as a result, it can be confirmed that if the diffraction period of the emission expansion area 53 is greater than 1.23×λ / n and less than 10.0×λ / n, even if the difference between the maximum value and the minimum value of the diffraction efficiency is reduced, the maximum value and the minimum value of the diffraction efficiency can be increased at the same time. That is, the utilization efficiency of the image light L1 from the display element 2 can be improved, and the degradation of the image quality of the virtual image Iv caused by the polarization state of the image light L1 can be reduced. Here, λ is the wavelength of the image light, and n is the refractive index of the emission expansion area 53. In the case where the diffraction structure of the emission expansion area 53 is a volume hologram element, the refractive index of the emission expansion area 53 is the refractive index of the volume hologram element.

[0105] [1.2 Examples and Comparative Examples]

[0106] 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 .

[0107] Tables 2 to 4 below respectively show parameters of image light and parameters of the diffractive structure related to the incident region 51 , the auxiliary expansion region 52 , and the emission expansion region 53 of Examples 1 to 4 and Comparative Examples 1 to 3.

[0108] Parameters of the image light related to the incident region 51 , the auxiliary expansion region 52 , and the exit expansion region 53 include θ_inx[°], θ_iny[°], θ_outx[°], and θ_outy[°].

[0109] θ_inx is Figure 3 θ_outx is the incident angle of the image light in the XZ plane of the light guide member 5. θ_outx is the emission angle of the image light in the XZ plane of the light guide member 5. Fig.11 Let's explain in more detail. Fig.11 yes Figure 3 FIG. 5 is an explanatory diagram of the incident angle θ_inx and the outgoing angle θ_outx of the image light in the XZ plane of the light guide member 5. Fig.11 In FIG. 5 , the diffraction structure 54 represents the diffraction structure of the incident region 51, the auxiliary expansion region 52, or the exit expansion region 53. The image light L11 represents the image light incident on the incident region 51, the auxiliary expansion region 52, or the exit expansion region 53. The image light L12 represents the image light emitted from the incident region 51, the auxiliary expansion region 52, or the exit expansion region 53 with the highest diffraction efficiency. Fig.11In θ_inx, θ_inx is the incident angle of the image light L11 incident on the diffractive structure 54 in a given plane (XZ plane) including the normal line N2 of the diffractive structure 54. Fig.11 In θ_outx, θ_outx is an emission angle of the image light L12 emitted from the diffractive structure 54 with the highest diffraction efficiency in a given plane (XZ plane) including the normal line N2 of the diffractive structure 54 .

[0110] θ_iny is Figure 3 θ_outy is the incident angle of the image light in the YZ plane of the light guide member 5. θ_outy is the outgoing angle of the image light in the YZ plane of the light guide member 5. Fig.12 Let's explain in more detail. Fig.12 yes Figure 3 FIG. 5 is an explanatory diagram of the incident angle θ_iny and the outgoing angle θ_outy of the image light in the YZ plane of the light guide member 5. Fig.12 In FIG. 5 , the diffraction structure 54 represents the diffraction structure of the incident region 51, the auxiliary expansion region 52, or the exit expansion region 53. The image light L11 represents the image light incident on the incident region 51, the auxiliary expansion region 52, or the exit expansion region 53. The image light L12 represents the image light emitted from the incident region 51, the auxiliary expansion region 52, or the exit expansion region 53 with the highest diffraction efficiency. Fig.12 In θ_iny, θ_iny is the incident angle of the image light L11 incident on the diffractive structure 54 in a given plane (YZ plane) including the normal line N2 of the diffractive structure 54. Fig.12 In θ_outy, θ_outy is an emission angle of the image light L12 emitted from the diffractive structure 54 with the highest diffraction efficiency in a given plane (YZ plane) including the normal line N2 of the diffractive structure 54 .

[0111] The parameters of the diffractive structure related to the incident area 51 include Figure 4 The parameters of the diffraction structure related to the auxiliary extension region 52 include Ga1[°] and Gp1[μm]. Figure 4 The parameters of the diffraction structure related to the emission expansion region 53 include Ga2[°] and Gp2[μm]. Figure 4 Ga3[°] and Gp3[μm] are shown.

[0112] [Table 2]

[0113]

[0114] [Table 3]

[0115]

[0116] [Table 4]

[0117]

[0118] Table 5 below shows the left and right sides of formula (1) and the presence or absence of useless light in Examples 1 to 4 and Comparative Examples 1 to 3. Substituting θ_iny in Table 4 as θ_in in formula (1) and θ_outy in Table 4 as θ_out in formula (1) to calculate the left and right sides of formula (1) in Table 5. In addition, in Examples 1 to 4 and Comparative Examples 1 to 3, the refractive index n of the main body 50 of the light guide member 5 is 1.505. In Examples 1, 3, 4 and Comparative Examples 1 and 3, the wavelength of the image light L1 is 0.52 [μm]. In Example 2 and Comparative Example 2, the wavelength of the image light L1 is 0.62 [μm].

[0119] [Table 5]

[0120]

[0121] When Example 1 is compared with Comparative Example 1, in the YZ plane, the presence of useless light is confirmed in Comparative Example 1, but the presence of useless light is not confirmed in Example 1. When Example 2 is compared with Comparative Example 2, in the YZ plane, the presence of useless light is confirmed in Comparative Example 2, but the presence of useless light is not confirmed in Example 2. When Example 3 is compared with Comparative Example 3, in the XY plane, in a plane tilted 7.12° from the Y-axis direction, the presence of useless light is confirmed in Comparative Example 3, but the presence of useless light is not confirmed in Example 3. In Example 4, the presence of useless light is not confirmed in the YZ plane.

[0122] According to Table 5, Examples 1 to 4 satisfy Formula (1), while Comparative Examples 1 to 3 do not satisfy Formula (1). Therefore, by satisfying the following Formula (1) for at least a portion of the emission expansion area 53, the generation of useless light in the emission expansion area 53 can be reduced. Thus, the utilization efficiency of the image light L1 from the display element 2 can be improved. In particular, in Examples 1 to 3, the emission angle θ_outy of the image light in the YZ plane of the light guide member 5 is greater than 15° and less than 45°, and the incident angle θ_iny of the image light in the YZ plane of the light guide member 5 is greater than 14° than the emission angle θ_outy. In addition, Examples 1 to 3 satisfy Formula (2). With respect to Examples 1 to 3, the first inclination angle and the second inclination angle of the image light L1 are not 0°, which are suitable for a head-up display. With respect to Example 4, the first inclination angle and the second inclination angle of the image light L1 are 0°, which are suitable for a head-mounted display.

[0123] [1.3, Effects, etc.]

[0124] 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 area 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 emission 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 L1C that propagate in a second propagation direction that intersects the first propagation direction, and emits the image light L1C from the light guide member 5. When at least a portion of the emission expansion region 53 is set such that the refractive index of the medium on the incident side of the image light with respect to the emission expansion region 53 and the refractive index of the medium on the exit side of the image light with respect to the emission expansion region 53 are equal to each other, the emission angle θ_out of the image light L1C emitted from the emission expansion region 53 with the highest diffraction efficiency in a given plane P1 including the normal line N of the emission expansion region 53 is greater than 15° and less than 45°, and the incident angle θ_in of the image light L1B incident on the emission expansion region 53 in the given plane P1 is greater than the emission angle θ_out by more than 14°. This structure can improve the utilization efficiency of the image light L1 from the display element 2.

[0125] In the optical system 3 , the following formula (1) is satisfied.

[0126] [Formula 10]

[0127]

[0128] This structure can improve the utilization efficiency of the image light L1 from the display element 2 .

[0129] In the optical system 3 , the following formula (2) is satisfied.

[0130] [Mathematical formula 11]

[0131]

[0132] This structure can improve the utilization efficiency of the image light L1 from the display element 2 .

[0133] 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 from the first oblique direction inclined relative to the normal line of the first surface 50a 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 along the second oblique direction inclined relative to the normal line of the second surface 50b. This structure can improve the utilization efficiency of the image light L1 from the display element 2.

[0134] In the optical system 3 , the first tilt direction and the second tilt direction are parallel to each other. This structure can improve the utilization efficiency of the image light L1 from the display element 2 .

[0135] 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.

[0136] 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.

[0137] In the optical system 3, the diffraction pitch of the emission expansion region 53 is greater than or equal to 1.23×λ / n and less than or equal to 10.0×λ / n. λ is the wavelength of the image light L1, L1A, L1B, L1C, and L2. n is the refractive index of the emission expansion region 53. This structure can improve the utilization efficiency of the image light L1 from the display element 2, and can reduce the degradation of the image quality of the optical image (virtual image Iv) caused by the polarization state of the image light L1.

[0138] In the optical system 3, at least a portion of the emission expansion region 53 is included in the end of the emission 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 emission expansion region 53. This structure can improve the utilization efficiency of the image light L1 from the display element 2.

[0139] 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.

[0140] 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.

[0141] The image display device 1 described above includes the optical system 3 and the display element 2. This structure can improve the utilization efficiency of the image light L1 from the display element 2.

[0142] [2. Modifications]

[0143] 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.

[0144] In a modified example, the diffraction structure of the emission expansion area 53 is not limited to a volume hologram element (holographic diffraction grating), but may be a surface relief type diffraction grating. When the surface relief type diffraction grating is a reflective type, the medium on the incident side of the image light relative to the emission expansion area 53 and the medium on the exit side of the image light relative to the emission expansion area 53 are both the main body 50 of the light guide member 5. When the surface relief type diffraction grating is a transmissive type, the medium on the incident side of the image light relative to the emission expansion area 53 is the main body 50 of the light guide member 5, but the medium on the exit side of the image light relative to the emission expansion area 53 is, for example, air. Regardless of whether the surface relief type diffraction grating is a reflective type or a transmissive type, when the refractive indexes of the medium on the incident side of the image light relative to the emission expansion area 53 and the medium on the exit side of the image light relative to the emission expansion area 53 are equal to each other, at least a portion of the emission expansion area 53 only needs to satisfy the formula (1).

[0145] Fig.13 This is a schematic diagram of a surface relief type diffraction grating. In particular, Fig.13 The surface relief type diffraction grating is a reflection type. The surface relief type diffraction grating generates a diffraction effect by periodically arranged concavoconvex parts 55. Fig.13 The concavoconvex part 55 is a groove. Fig.13 In the embodiment, the direction of the Z2 axis is the thickness direction of the surface relief type diffraction grating. The directions of the X2 axis and the Y2 axis are orthogonal to the direction of the Z2 axis and are orthogonal to each other. The direction of the X2 axis is the direction in which the concavoconvex portions 55 extend. The direction of the Y2 axis is the direction in which the concavoconvex portions 55 are arranged. Fig.13 Gp represents the diffraction period (diffraction pitch) [μm] of the surface relief type diffraction grating. Figure 4 The diffraction period Gp3 of the exit expansion region 53 may correspond to Fig.13 The diffraction period Gp. Figure 4 The angle Ga3 of the emission expansion region 53 may correspond to the direction of the Y axis in a plane (in the XY plane) perpendicular to the thickness direction of the main body 50. Fig.13 The angle of the surface relief type diffraction grating in the direction of the X2 axis. The surface relief type diffraction grating is not limited to the same material as the light guide component 5, and can also be formed by a different material. For example, the material of the light guide component 5 can be glass, and the material of the surface relief type diffraction grating can be ultraviolet curing resin. In this case, the surface relief type diffraction grating can be formed by nanoimprinting technology. In addition, in the case where the diffraction structure of the output expansion area 53 is a surface relief type diffraction grating, the refractive index of the output expansion area 53 is the refractive index of the material forming the surface relief type diffraction grating.

[0146] In a modified example, the diffraction structure of the incident area 51 and the auxiliary expansion area 52 is not limited to a volume hologram element (holographic diffraction grating), and can be a surface relief type diffraction grating. In a modified example, the incident area 51 and the auxiliary expansion area 52 can have a half mirror. The light guide component 5 may not have the auxiliary expansion area 52. That is, the light guide component 5 may be a structure that performs a pupil expansion on one axis instead of a two-axis pupil expansion. In this case, the incident area 51 changes the traveling direction of the image light L1 incident on the incident area 51, and causes it to propagate in the main body 50 as the image light L1B along the first propagation direction. The output expansion area 53 only needs to divide the image light L1B from the incident area 51 in the first propagation direction into a plurality of image lights L1C propagating in the second propagation direction, and emit them from the light guide component 5.

[0147] In a modified example, the diffraction pitch of the emission expansion region 53 is greater than or equal to 1.36×λ / n and less than or equal to 3.82×λ / n. λ is the wavelength of the image light L1. n is the refractive index of the main body 50. In this way, the utilization efficiency of the image light L1 from the display element 2 can be improved. 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.

[0148] In a modified example, in the optical system 3, the range of the incident angle θ_in that is greater than the exit angle θ_out by 14° or more or satisfies the formula (1) includes a range determined by the incident angle of the secondary light rays that are related to the given plane P1 and define the two outer edges of the image light L1B incident on the exit expansion area 53. In practice, the image light L1B often has a certain degree of expansion, and sometimes the angles at which the primary light ray and the secondary light ray of the image light L1B are incident on the exit expansion area 53 are different. Therefore, in order to further improve the utilization efficiency of the image light L1 from the display element 2, it is preferred that all the light rays included in the image light L1B are greater than the exit angle θ_out by 14° or more or satisfy the formula (1). That is, by making the range of the incident angle θ_in greater than the exit angle θ_out by 14° or more or satisfying the formula (1) include the range determined by the incident angle of the secondary light rays related to the given plane P1 and defining the two outer edges of the image light L1B incident on the exit expansion area 53, the generation of useless light can be reduced for all the light rays included in the image light L1B. In this way, the utilization efficiency of the image light L1 from the display element 2 can be further improved in the entire field of view area Ac.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] 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.

[0154] 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 this 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 polarized light 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.

[0155] [3. Method]

[0156] 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.

[0157] 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 (L1C) propagating in a second propagation direction intersecting with the first propagation direction, and emitting the image light from the light guide member (5). When at least a portion of the emission expansion region (53) is set such that the refractive indexes of a medium on the incident side of the image light (L1B) relative to the emission expansion region (53) and a medium on the exit side of the image light (L1B) relative to the emission expansion region (53) are equal to each other, an emission angle θ_out of the image light (L1C) emitted from the emission expansion region (53) with the highest diffraction efficiency within a given plane (P1) including a normal line (N) of the emission expansion region (53) is greater than 15° and less than 45°, and an incident angle θ_in of the image light (LIB) incident on the emission expansion region (53) within the given plane (P1) is greater than the emission angle θ_out by more than 14°. This method can improve the utilization efficiency of the image light (L1) from the display element (2).

[0158] The second aspect is an optical system (3) based on the first aspect. In this aspect, the following formula (1) is satisfied.

[0159] [Mathematical formula 12]

[0160]

[0161] This method can improve the utilization efficiency of image light (L1) from the display element (2).

[0162] The third aspect is an optical system (3) based on the first or second aspect. In this aspect, the following formula (2) is satisfied.

[0163] [Mathematical formula 13]

[0164]

[0165] This method can improve the utilization efficiency of image light (L1) from the display element (2).

[0166] The fourth aspect is an optical system (3) based on any one of the first to third aspects. 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) causes the image light (L1) incident on the first surface (50a) from a first inclined direction inclined relative to the normal line of the first surface (50a) to be incident on 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) along the second inclined direction inclined relative to the normal line of the second surface (50b). This aspect can improve the utilization efficiency of the image light (L1) from the display element (2).

[0167] A fifth aspect is an optical system (3) based on the fourth aspect. In this aspect, the first tilt direction and the second tilt direction are parallel to each other. This aspect can improve the utilization efficiency of the image light (L1) from the display element (2).

[0168] A sixth aspect is an optical system (3) according to any one of the first to fifth 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).

[0169] 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.

[0170] The eighth mode is an optical system (3) based on any one of the first to seventh modes. In this mode, the diffraction spacing of the emission expansion region (53) is greater than 1.23×λ / n and less than 10.0×λ / n. λ is the wavelength of the image light (L1, L1A, L1B, L1C, L2). n is the refractive index of the emission expansion region (53). This mode can improve the utilization efficiency of the image light (L1) from the display element (2), and can reduce the degradation of the image quality of the optical image (virtual image Iv) caused by the polarization state of the image light (L1).

[0171] The ninth aspect is an optical system (3) based on any one of the first to eighth aspects. In this aspect, the diffraction pitch of the emission expansion region (53) is greater than or equal to 1.36×λ / n and less than or equal to 3.82×λ / n. λ is the wavelength of the image light (L1, L1A, L1B, L1C, L2). n is the refractive index of the emission expansion region (53). This aspect can improve the utilization efficiency of the image light (L1) from the display element (2).

[0172] The tenth mode is an optical system (3) based on any one of the first to ninth modes. In this mode, the range of the incident angle θ_in that is greater than the exit angle θ_out by 14° or more includes a range determined by the incident angle of the secondary light rays that are related to the given plane (P1) and define the two outer edges of the image light incident on the exit expansion area (53). This mode can further improve the utilization efficiency of the image light (L1) from the display element (2).

[0173] The eleventh aspect is an optical system (3) according to any one of the first to tenth aspects. In this aspect, the at least a portion of the emission expansion region (53) is included in an optical path of the image light (L1) from the incident region (51) to the emission expansion region (53), at an end of the emission expansion region (53) on the incident region (51) side. This aspect can improve the utilization efficiency of the image light (L1) from the display element (2).

[0174] The twelfth aspect is an optical system (3) according to any one of the first to eleventh 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.

[0175] A thirteenth aspect is an optical system (3) according to any one of the first to twelfth 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).

[0176] A fourteenth aspect is an image display device (1) comprising an optical system (3) according to any one of the first to thirteenth aspects and the display element (2). This aspect can improve the utilization efficiency of image light (L1) from the display element (2).

[0177] The above-mentioned second to thirteenth aspects are not essential.

[0178] 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.

[0179] Industrial Applicability

[0180] 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.

[0181] Description of Reference Numerals

[0182] 1 Image display device

[0183] 2Display components

[0184] 3. Optical system

[0185] 5 Light guide components

[0186] 50 Main body

[0187] 50a Side 1

[0188] 50b Side 2

[0189] 51Incident area

[0190] 52 auxiliary expansion area

[0191] 53 Exit expansion area

[0192] 6Projection optical system

[0193] 100 moving bodies

[0194] 101 Windshield (light-transmitting component)

[0195] Ac visual field

[0196] D User

[0197] IV virtual image (optical image)

[0198] L1, L1A, L1B, L1C, L2 Image light

[0199] N Normals

[0200] Refractive index

[0201] P1 given plane

[0202] θ_in Incident angle

[0203] θ_out Output angle

[0204] λ Wavelength.

Claims

1. An optical system comprising: The light guide member guides the image light output from the display element to form an image to the user's field of view 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 lights from the light guide member; When at least a portion of the emission expansion region is set such that the refractive index of a medium on the incident side of the image light relative to the emission expansion region and the refractive index of a medium on the exit side of the image light relative to the emission expansion region are equal to each other, The emission angle θ_out of the image light emitted from the emission expansion area with the highest diffraction efficiency within a given plane including the normal line of the emission expansion area is greater than or equal to 15° and less than or equal to 45°, An incident angle θ_in of the image light incident on the exit expansion region in the given plane is greater than the exit angle θ_out by more than 14°.

2. The optical system according to claim 1, wherein: The optical system satisfies the following formula (1): [Mathematical formula 1] 。 3. The optical system according to claim 1, wherein: The optical system satisfies the following formula (2): [Mathematical formula 2] 。 4. The optical system according to claim 1, 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 from a first oblique direction inclined with respect to a normal line of the first surface 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 along a second oblique direction inclined with respect to a normal line of the second surface.

5. The optical system according to claim 4, wherein: The first inclined direction and the second inclined direction are parallel to each other.

6. The optical system according to any one of claims 1 to 5, wherein: The diffractive structure of the emission expansion region is a volume hologram element located inside the main body.

7. The optical system according to any one of claims 1 to 5, 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 any one of claims 1 to 5, wherein: The diffraction spacing of the emission expansion region is greater than or equal to 1.23×λ / n and less than or equal to 10.0×λ / n, λ is the wavelength of the image light, n is the refractive index of the exit expansion region.

9. The optical system according to any one of claims 1 to 5, wherein: The diffraction spacing of the emission expansion region is greater than or equal to 1.36×λ / n and less than or equal to 3.82×λ / n, λ is the wavelength of the image light, n is the refractive index of the exit expansion region.

10. The optical system according to any one of claims 1 to 5, wherein: The range of the incident angle θ_in that is greater than the exit angle θ_out by 14° or more includes a range determined by the incident angles of the secondary rays that are related to the given plane and define the two outer edges of the image light incident on the exit expansion area.

11. The optical system according to any one of claims 1 to 5, wherein: The at least a portion of the emission expansion region is included in an end portion of the emission expansion region on the incident region side on an optical path of the image light from the incident region to the emission expansion region.

12. The optical system according to any one of claims 1 to 5, 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.

13. The optical system according to any one of claims 1 to 5, wherein: The invention 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.

14. An image display device comprising: The optical system according to any one of claims 1 to 5; and The display element.

Images