WO2023008576A1

WO2023008576A1 - Combiner, head-up display, mobile body, and automobile

Info

Publication number: WO2023008576A1
Application number: PCT/JP2022/029373
Authority: WO
Inventors: 豪山内; 悟吉田; 啓介三浦; 陽祐青木; 寛行國安
Original assignee: 大日本印刷株式会社
Priority date: 2021-07-30
Filing date: 2022-07-29
Publication date: 2023-02-02

Abstract

A combiner 40 is used for a head-up display 20 and receives image light projected thereto. The combiner 40 has: a first substrate 51 that includes a first surface 41 serving as an incident surface for image light; a second substrate 52 that includes a second surface 42; a bonding layer 45 that bonds the first substrate 51 and the second substrate 52; and a holographic element 60 located between the first substrate 51 and the second substrate 52. The holographic element 60 diffracts image light: in a direction of positive reflection relative to the direction of incidence of the image light upon the combiner 40; or in a direction inclined at an angle of 5° or less to the direction of positive reflection. A distance LX between the holographic element 60 and a display position PX of an imaginary image 80 that is caused by the image light diffracted by the holographic element 60 is four or more times greater than a distance LY between the holographic element 60 and a display position PY of a ghost image 81 that is caused by the image light reflected by the first surface 41 or the second surface 42.

Description

Combiners, head-up displays, mobiles, and automobiles

The present disclosure relates to combiners, head-up displays, moving bodies, and automobiles.

The head-up display displays within the user's field of view. The head-up display has a transparent combiner. Image light is projected onto the combiner. In the head-up display disclosed in Patent Document 1 (JP2000-35513A), the combiner includes a hologram element. The hologram element diffracts the image light and directs it to the user. A user can observe the images in the combiner. Also, the user can secure a field of view through the transparent combiner.

When the combiner disclosed in Patent Document 1 is used, noise images such as the sun and outdoor lights can be observed brightly inside the combiner. The noise image is observed at a position different from the actual position, and the user feels uncomfortable with the noise image. Also, part of the image light is specularly reflected on the surface of the combiner to form a ghost image. Noise images and ghost images can degrade the display quality of the head-up display.

The present disclosure aims at improving the display quality of the head-up display.

An embodiment of the present disclosure relates to the following [1] to [30].

[1] A combiner for a head-up display that projects image light,
a first substrate including a first surface serving as an incident surface of the image light;
a second substrate including a second surface facing the first surface;
a bonding layer that bonds the first substrate and the second substrate;
a hologram element positioned between the first substrate and the second substrate;
the hologram element diffracts the image light in a direction of specular reflection with respect to the direction of incidence of the image light on the combiner or in a direction inclined at an angle of 25° or less to the direction of specular reflection;
The distance between the display position of the image by the image light diffracted by the hologram element and the hologram element is the distance between the display position of the image by the image light reflected by the first surface or the second surface and the hologram element. A combiner that is more than four times.

[2] A combiner for a head-up display that projects image light,
a first substrate including a first surface serving as an incident surface of the image light;
a second substrate including a second surface facing the first surface;
a bonding layer that bonds the first substrate and the second substrate;
a hologram element positioned between the first substrate and the second substrate;
An image of an external light source reproduced by light emitted from an external light source, incident on the combiner from the second surface, reflected by the first surface and then diffracted by the hologram element is observed through the combiner. A combiner that is viewed at least partially overlapping a real image of an external light source that is viewed.

[3] The distance between the display position of the image by the image light diffracted by the hologram element and the hologram element is the distance between the display position of the image by the image light reflected by the first surface or the second surface and the hologram element. The combiner for the head-up display of [2], which is more than four times the distance of .

[4] The combiner for a head-up display according to any one of [1] to [3], wherein the first substrate includes an antireflection layer forming the first surface.

[5] A combiner for a head-up display that projects image light,
a first substrate including a first surface serving as an incident surface of the image light;
a second substrate including a second surface facing the first surface;
a bonding layer that bonds the first substrate and the second substrate;
a hologram element positioned between the first substrate and the second substrate;
the hologram element diffracts the image light in a direction of specular reflection with respect to the direction of incidence of the image light on the combiner or in a direction inclined at an angle of 25° or less to the direction of specular reflection;
A combiner for a head-up display, wherein the first substrate includes an antireflection layer forming the first surface.

[6] a projection device that emits image light;
A head-up display comprising a combiner according to any one of [1] to [5].

[7] The head-up display of [6], wherein the difference between the angle of incidence of the image light on the combiner and the angle of diffraction of the image light at the combiner is 3° or more.

[8] The head-up display of [6] or [7], wherein the angle of diffraction of the image light at the combiner is greater than the angle of incidence of the image light on the combiner.

[9] A light shielding member is provided so as to be offset from the optical path of the image light emitted from the projection device and diffracted by the hologram element of the combiner,
The head-up display according to any one of [6] to [8], wherein the light blocking plate blocks part of the image light emitted from the projection device and directed toward the combiner.

[10] The projection device includes an image forming device that emits the image light, and an optical path adjusting member that is arranged between the image forming device and the combiner and adjusts an optical path of the image light,
The head-up display according to any one of [6] to [9], wherein the optical path adjusting member has an anisotropic diffusion function.

[11] The optical path adjustment member is perpendicular to the first evaluation surface and the The head-up display of [10], which has a strong diffusion function in the second evaluation plane parallel to the optical axis.

[12] A moving body equipped with a head-up display according to any one of [6] to [11].

[13] A head-up display according to any one of [6] to [11],
The automobile, wherein the optical path length of the image light from the projection device to the combiner is 200 mm or more.

[14] A head-up display according to any one of [6] to [11],
The formula "Lz × sin θ4" using the optical path length Lz (mm) and the angle θ4 (°) is 10 mm or more,
The optical path length Lz (mm) is the optical path length of the image light from the combiner to the projection device,
The motor vehicle, wherein the angle θ4 is the difference between the magnitude of the incident angle of the image light to the combiner and the magnitude of the diffraction angle of the image light at the combiner.

[15] Equipped with a head-up display according to any one of [6] to [11],
The motor vehicle, wherein the diffraction angle of the image light at the combiner is 30° or more.

[16] Equipped with a head-up display of any one of [6] to [11],
The sum of the tilt angle of the combiner and the incident angle of the image light to the combiner is 70° or more,
The motor vehicle, wherein the tilt angle of the combiner is the angle between the normal direction and the vertical direction of the combiner.

[17] A head-up display according to any one of [6], [7], [9] to [11],
A motor vehicle, wherein a magnitude of an angle of diffraction of said image light at said combiner is smaller than a magnitude of an angle of incidence of said image light on said combiner.

[18] A head-up display according to any one of [6] to [11],
A motor vehicle, wherein part of the image light is reflected by the first surface or the second surface in a direction inclined upward with respect to a horizontal direction.

[19] the magnitude of the incident angle of the image light to the combiner is greater than the magnitude of the tilt angle of the combiner;
The vehicle of [17] or [18], wherein the tilt angle of the combiner is the angle between the normal direction of the combiner and the vertical direction.

[20] A head-up display according to any one of [6] to [11],
The tilt angle of the combiner is 25° or more and 55° or less,
the magnitude of the incident angle of the image light to the combiner is greater than the magnitude of the tilt angle of the combiner by an angle greater than 0° and less than or equal to 60°;
The motor vehicle, wherein the tilt angle of the combiner is the angle between the normal direction and the vertical direction of the combiner.

[21] A head-up display comprising a projection device that emits image light and a combiner that projects the image light,
The combiner is
a first substrate including a first surface serving as an incident surface of the image light;
a second substrate including a second surface facing the first surface;
a bonding layer that bonds the first substrate and the second substrate;
a hologram element positioned between the first substrate and the second substrate;
The head-up display, wherein a diffraction angle of the image light at the combiner is larger than an incident angle of the image light to the combiner.

[22] A motor vehicle with a head-up display,
The head-up display includes a projection device that emits image light and a combiner that projects the image light,
The combiner is
a first substrate including a first surface serving as an incident surface of the image light;
a second substrate including a second surface facing the first surface;
a bonding layer that bonds the first substrate and the second substrate;
a hologram element positioned between the first substrate and the second substrate;
The automobile, wherein the optical path length of the image light from the projection device to the combiner is 200 mm or more.

[23] A motor vehicle with a head-up display,
The head-up display includes a projection device that emits image light and a combiner that projects the image light,
The combiner is
a first substrate including a first surface serving as an incident surface of the image light;
a second substrate including a second surface facing the first surface;
a bonding layer that bonds the first substrate and the second substrate;
a hologram element positioned between the first substrate and the second substrate;
The formula "Lz × sin θ4" using the optical path length Lz (mm) and the angle θ4 (°) is 10 mm or more,
The optical path length Lz (mm) is the optical path length of the image light from the projection device to the combiner,
The motor vehicle, wherein the angle θ4 (°) is a difference between an incident angle of the image light to the combiner and a diffraction angle of the image light at the combiner.

[24] A motor vehicle with a head-up display,
The head-up display includes a projection device that emits image light and a combiner that projects the image light,
The combiner is
a first substrate including a first surface serving as an incident surface of the image light;
a second substrate including a second surface facing the first surface;
a bonding layer that bonds the first substrate and the second substrate;
a hologram element positioned between the first substrate and the second substrate;
The motor vehicle, wherein the diffraction angle of the image light at the combiner is 30° or more.

[25] A motor vehicle comprising a head-up display,
The head-up display includes a projection device that emits image light and a combiner that projects the image light,
The combiner is
a first substrate including a first surface serving as an incident surface of the image light;
a second substrate including a second surface facing the first surface;
a bonding layer that bonds the first substrate and the second substrate;
a hologram element positioned between the first substrate and the second substrate;
The sum of the inclination angle of the combiner and the incident angle of the image light to the combiner is 70° or more,
The motor vehicle, wherein the tilt angle of the combiner is the angle between the normal direction and the vertical direction of the combiner.

[26] A motor vehicle with a head-up display,
The head-up display includes a projection device that emits image light and a combiner that projects the image light,
The combiner is
a first substrate including a first surface serving as an incident surface of the image light;
a second substrate including a second surface facing the first surface;
a bonding layer that bonds the first substrate and the second substrate;
a hologram element positioned between the first substrate and the second substrate;
A motor vehicle, wherein a magnitude of an angle of diffraction of said image light at said combiner is smaller than a magnitude of an angle of incidence of said image light on said combiner.

[27] A motor vehicle with a head-up display,
The head-up display includes a projection device that emits image light and a combiner that projects the image light,
The combiner is
a first substrate including a first surface serving as an incident surface of the image light;
a second substrate including a second surface facing the first surface;
a bonding layer that bonds the first substrate and the second substrate;
a hologram element positioned between the first substrate and the second substrate;
A motor vehicle, wherein part of the image light is reflected by the first surface or the second surface in a direction inclined upward with respect to a horizontal direction.

[28] A motor vehicle comprising a head-up display,
The head-up display includes a projection device that emits image light and a combiner that projects the image light,
The combiner is
a first substrate including a first surface serving as an incident surface of the image light;
a second substrate including a second surface facing the first surface;
a bonding layer that bonds the first substrate and the second substrate;
a hologram element positioned between the first substrate and the second substrate;
The tilt angle of the combiner is 25° or more and 55° or less,
the magnitude of the incident angle of the image light to the combiner is greater than the magnitude of the tilt angle of the combiner by an angle greater than 0° and less than or equal to 60°;
The motor vehicle, wherein the tilt angle of the combiner is the angle between the normal direction and the vertical direction of the combiner.

[29] An image forming device that emits image light;
a combiner projected with the image light;
an optical path adjustment member disposed between the image forming apparatus and the combiner and adjusting an optical path of the image light;
The combiner is
a first substrate including a first surface serving as an incident surface of the image light;
a second substrate including a second surface facing the first surface;
a bonding layer that bonds the first substrate and the second substrate;
a hologram element positioned between the first substrate and the second substrate;
The magnitude of the diffraction angle of the image light at the combiner is different from the magnitude of the incident angle of the image light to the combiner,
the hologram element diffracts the image light in a direction inclined with respect to a specular reflection direction with respect to an incident direction of the image light to the combiner;
The optical path adjustment member is perpendicular to the first evaluation surface and the optical path of the combiner rather than in the first evaluation surface parallel to both the normal direction of the combiner and the optical axis of the image light incident on the combiner. A head-up display having a strong diffusion function in a second evaluation plane parallel to the normal direction.

[30] A head-up display comprising a projection device that emits image light and a combiner that projects the image light,
The combiner is
a first substrate including a first surface serving as an incident surface of the image light;
a second substrate including a second surface facing the first surface;
a bonding layer that bonds the first substrate and the second substrate;
a hologram element positioned between the first substrate and the second substrate;
The head-up display according to claim 1, wherein a difference between an incident angle of the image light to the combiner and a diffraction angle of the image light at the combiner is 3° or more.

According to the present disclosure, the display quality of the head-up display can be improved.

FIG. 1 is a diagram for explaining an embodiment, and is a side view showing a specific example of a moving body and a head-up display. 2 is a side sectional view showing the combiner of the head-up display shown in FIG. 1; FIG. 3A is a cross-sectional view showing an example of a first substrate that may be included in the combiner shown in FIG. 2. FIG. 3B is a cross-sectional view showing another example of a first substrate that can be included in the combiner shown in FIG. 2. FIG. 3C is a cross-sectional view showing yet another example of a first substrate that can be included in the combiner shown in FIG. 2. FIG. FIG. 4 is a diagram illustrating a method of manufacturing a hologram recording layer that can be included in the combiner shown in FIG. 2; 5 is a graph showing an example of spectral transmittance of a hologram element that can be included in the combiner shown in FIG. 2. FIG. FIG. 6 is a diagram illustrating the operation of the combiner shown in FIG. 2; FIG. 7 is a diagram illustrating the operation of the combiner shown in FIG. 2; FIG. 8 is a cross-sectional view showing the configuration of samples 1 to 5. FIG. FIG. 9 is a diagram explaining the action of the combiner. FIG. 10 is a diagram explaining the operation of the combiner. FIG. 11 is a diagram corresponding to FIG. 7 and for explaining the operation of the combiner. FIG. 12 is a diagram corresponding to FIG. 7 and for explaining the action of the combiner. FIG. 13 is a diagram for explaining the action of the combiner. FIG. 14 is a graph showing an example of the angular distribution of luminance on the most light-emitting surface of the optical path adjusting member. FIG. 15 is a perspective view showing an example of an optical path adjustment member. FIG. 16 is a perspective view showing another example of the optical path adjusting member. FIG. 17 is a perspective view showing still another example of the optical path adjustment member.

An embodiment of the present disclosure will be described below with reference to the drawings. In the drawings attached to this specification, for the convenience of illustration and ease of understanding, the scale and the ratio of vertical and horizontal dimensions are changed and exaggerated from those of the real thing. In addition, configurations and the like shown in some drawings may be omitted in other drawings.

In this specification, terms that specify shapes and geometric conditions and their degrees, such as "parallel", "perpendicular", "identical", length and angle values, etc., are limited to strict meanings. It is interpreted to include the extent to which similar functions can be expected without being

In this specification, terms such as "sheet", "film" and "plate" are not distinguished from each other based only on the difference in designation. For example, a "transparent plate" cannot be distinguished from a member called a transparent film or a transparent sheet only by the difference in name.

In this specification, the normal direction of the sheet-like (film-like, plate-like) member refers to the normal direction to the sheet surface of the target sheet-like (film-like, plate-like) member. In addition, the "sheet surface (film surface, plate surface)" refers to the sheet-like member (film-like) that is the target when the target sheet-like (film-like, plate-like) member is viewed as a whole and from a broad perspective. member, plate-shaped member).

In order to clarify the directional relationships among the figures, some of the figures show the first direction D1, the second direction D2, the third direction D3 and the normal direction ND as common directions by means of commonly labeled arrows. is shown as In the following examples, the first direction D1 and the second direction D2 are parallel to the horizontal direction, and the third direction D3 is parallel to the vertical direction. An arrow pointing forward from the plane of the drawing along a direction perpendicular to the plane of the drawing is indicated by a dot in a circle, as shown in FIG. 2, for example.

1 to 17 are diagrams for explaining one embodiment. As shown in FIGS. 1 and 2, the head-up display 20 has a projection device 25 and a combiner 40. FIG. The head-up display 20 uses the combiner 40 to display the image formed by the projection device 25 toward the user 5 . A user 5 of the head-up display 20 can observe behind the combiner 40 through the combiner 40 . An imaging device may image the user 5 observing the combiner 40 via the combiner 40 . This embodiment is designed to make the noise image 91, which has been a problem in the conventional head-up display, inconspicuous. An embodiment will now be described with reference to specific examples shown in the drawings.

The head-up display 20 according to this embodiment is applicable to various fields. Head-up display 20 may be applied to a head-mounted display. A heads-up display 20 may be applied to the prompter. The prompter may be used for lectures, imaging, and the like.

In the illustrated example, the head-up display 20 is applied to the moving body 10. The moving body 10 is a movable device. The mobile object 10 may be movable with a person on it. Examples of mobile objects 10 include ships, airplanes, drones, railway vehicles, and illustrated automobiles 12 . In the example shown in FIG. 1 , the combiner 40 constitutes the windshield 14 of the motor vehicle 12 .

The projection device 25 emits image light that forms an image. A user 5 observes the image by receiving the image light. The projection device 25 is not particularly limited, and various devices capable of forming an image can be used. In the example shown in FIG. 1, the projection device 25 is arranged in the dashboard. The projection device 25 is hidden by the dashboard.

The projection device 25 includes an image forming device 30 . Projection device 25 may include a glare trap. Image forming apparatus 30 may employ a dot matrix method. The dot matrix image forming apparatus 30 includes a plurality of pixels forming each dot. This image forming apparatus 30 forms a desired image by controlling the light emission state of each pixel. Examples of the image forming device 30 include a transmissive liquid crystal display device, a reflective liquid crystal display device, a laser display device, an electroluminescence display device also called an EL display device, a digital mirror device, and the like. The glare trap may be the tip of the image forming device 30 that emits image light. The glare trap may constitute the image emitting surface of the imaging device 30 . The glare trap may include a low reflection film, an antiglare sheet, or the like.

The image light from the image forming device 30 is projected onto the combiner 40 . The projection device 25 may include an optical path adjustment member 34 indicated by a two-dot chain line in FIG. The optical path adjusting member 34 adjusts the optical path of image light from the image forming apparatus 30 to the combiner 40 . The optical path adjustment member 34 may be the projection optical system 35 . Projection optics 35 guide image light from image forming device 30 to combiner 40 . Projection optics 35 may include mirrors, lenses, prisms, diffractive optical elements, and combinations thereof.

The optical path adjustment member 34 may include an optical sheet and a light source that illuminates the optical sheet from behind. The optical sheet may include a transparent film and a printed layer having visible light transmittance printed on the transparent film. As another example, the optical sheet may be a light shielding plate provided with openings and transmissive portions. The light source may be a surface light source device that emits light in a planar manner. According to these display devices, display corresponding to the optical sheet, such as pictograms and marks, can be displayed.

The combiner 40 directs the image light from the projection device 25 to the user 5, as shown in FIG. As shown in FIG. 2 , the combiner 40 may include a first substrate 51 , a second substrate 52 , a bonding layer 45 and a hologram element 60 . Combiner 40 may have a high visible light transmission. Combiner 40 may be transparent. Combiner 40 may be transparent if the incident light does not satisfy the Bragg condition of hologram element 60 . Components of combiner 40 may also be transparent to provide combiner 40 with high visible light transmission.

"Transparent" as used herein means that the visible light transmittance is 50% or more, preferably 80% or more. The visible light transmittance is measured using a spectrophotometer ("UV-3100PC" manufactured by Shimadzu Corporation, compliant with JISK0115) at an incident angle of 0° for every 1 nm within a measurement wavelength range of 380 nm or more and 780 nm or less. , is specified as the average value of the total light transmittance at each wavelength. The incident angle is the angle (°) formed by the traveling direction of the incident light with respect to the normal direction to the plane of incidence, and is less than 90°.

The combiner 40 has a first surface 41 and a second surface 42 . In the example shown in FIG. 2, the combiner 40 is plate-shaped. The combiner 40 has a normal direction ND. The first surface 41 and the second surface 42 form a pair of main surfaces of the combiner 40 . The first surface 41 and the second surface 42 face each other in the normal direction ND. The first surface 41 and the second surface 42 spread in a direction perpendicular to the normal direction ND. In the example shown in FIG. 2 , the first substrate 51 constitutes the first surface 41 and the second substrate 52 constitutes the second surface 42 . The first surface 41 serves as an incident surface for image light from the projection device 25 .

The first substrate 51 and the second substrate 52 are stacked in the normal direction ND. The bonding layer 45 is located between the first substrate 51 and the second substrate 52 in the normal direction ND. The bonding layer 45 is in direct or indirect contact with the first substrate 51 and the second substrate 52 . The bonding layer 45 is bonded to the first substrate 51 and the second substrate 52 . As a result, the bonding layer 45 bonds the first substrate 51 and the second substrate 52 together.

The hologram element 60 is positioned between the first substrate 51 and the second substrate 52 in the normal direction ND. The hologram element 60 is in direct or indirect contact with the bonding layer 45 at least partially. In the illustrated example, the hologram element 60 is separated from both the first substrate 51 and the second substrate 52 in the normal direction ND. A bonding layer 45 is positioned between the hologram element 60 and the first substrate 51 . A bonding layer 45 is positioned between the hologram element 60 and the second substrate 52 . The hologram element 60 is in contact with the bonding layer 45 on all its outer surfaces.

In the illustrated example, the normal direction ND of the combiner 40 is the normal direction of the first surface 41, the normal direction of the second surface 42, the normal direction of the first substrate 51, and the normal direction of the second substrate 52. , the normal direction of the bonding layer 45 , and the normal direction of the hologram element 60 . For convenience of understanding, the combiner 40 is shown in a flat plate shape in FIG. 2 and the like. As shown in FIG. 1, combiner 40 may be curved. For example, combiner 40 may be curved to follow the shape of windshield 14 .

The first substrate 51 and the second substrate 52 are transparent plates. The first substrate 51 and the second substrate 52 function as substrates that support the hologram element 60 . In the illustrated example, the first substrate 51 and the second substrate 52 function as windshield members. As a material for the first substrate 51 and the second substrate 52, a glass such as soda lime glass or soda lime glass may be used. As a material for the first substrate 51 and the second substrate 52, a resin such as acrylic resin or polycarbonate may be used. The thickness along the normal direction ND of the first substrate 51 and the second substrate 52 may be 1 mm or more and 5 mm or less. The first substrate 51 and the second substrate 52 may be identically configured with the same material, may be configured with different materials, or may have different configurations.

The first substrate 51 and the second substrate 52 may include multiple layers, as indicated by the two-dot chain lines in FIG. At least one of first substrate 51 and second substrate 52 may include transparent plate 56 and antireflection layer 57 . The antireflection layer 57 may constitute the first surface 41 , which is the outermost surface of the combiner 40 . The antireflection layer 57 may constitute the second surface 42 , which is the outermost surface of the combiner 40 .

The transparent plate 56 may be a glass plate such as soda lime glass or blue plate glass. The transparent plate 56 may be a resin plate such as acrylic resin or polycarbonate.

The antireflection layer 57 suppresses reflection of light. The antireflection layer 57 may employ various configurations capable of suppressing reflection. Antireflection layer 57 may have the configuration shown in FIGS. 3A-3C. FIG. 3A shows a single layer antireflection layer 57 . The antireflection layer 57 shown in FIG. 3A has a low refractive index lower than the refractive index of the layer (the transparent plate 56 in the illustrated example) adjacent to this antireflection layer 57 in the normal direction ND. Layer 57a. The antireflection layer 57 shown in FIG. 3B includes a low refractive index layer 57a and a high refractive index layer 57b in order from the outermost surface in the normal direction ND. The antireflection layer 57 shown in FIG. 3C includes multiple low refractive index layers 57a and multiple high refractive index layers 57b. In the example shown in FIG. 3C, the low refractive index layers 57a and the high refractive index layers 57b are repeatedly arranged in order from the first surface 41 side in the normal direction ND. In the example shown in FIGS. 3A-3C, antireflection layer 57 suppresses reflections by causing light reflected at different optical interfaces to cancel. The thickness and refractive index of the layers included in the antireflection layer 57 can be appropriately selected according to the wavelength of light whose reflection is to be suppressed. The thickness of the low refractive index layer 57a and the high refractive index layer 57b included in the antireflection layer 57 is less than 780 nm.

The low refractive index layer 57a and the high refractive index layer 57b can be produced by applying a liquid ultraviolet curable resin composition to form a layer and irradiating the layer with ultraviolet rays. The liquid ultraviolet curable resin composition for making the low refractive index layer 57a contains (a) particles for adjusting the refractive index, such as hollow silica, (b) an initiator, and (c) a fluorine additive. It may include the above. The liquid ultraviolet curable resin composition for producing the high refractive index layer 57b may contain one or more of (d) particles for adjusting the refractive index, such as a high refractive index filler, and (e) an initiator. The low refractive index layer 57a and the high refractive index layer 57b can also be produced by physical vapor deposition such as vacuum deposition and sputtering.

From the viewpoint of making a noise image 91 and a ghost image 81 (to be described later) inconspicuous, the reflectance on the surface of the combiner 40 constituted by the antireflection layer 57 may be 1% or less, or 0.5% or less. The reflectance is measured using a spectrophotometer ("UV-3100PC" manufactured by Shimadzu Corporation, compliant with JISK0115) at intervals of 1 nm within a range of measurement wavelengths of 400 nm or more and 700 nm or less. specified as the maximum value. The angle of incidence for measuring the reflectance is the angle of incidence on the combiner 40 at which the diffraction efficiency of the hologram element 60 takes the maximum value. However, if the incident angle to the combiner 40 at which the diffraction efficiency of the hologram element 60 takes the maximum value is less than 5°, it becomes difficult to measure the reflectance. 5°. The incident angle is the angle (°) formed by the traveling direction of the incident light with respect to the normal direction to the plane of incidence, and is less than 90°. The reflectance of the combiner 40 is measured with a black sheet attached to the surface of the combiner 40 opposite to the incident surface. As the black sheet, a sheet having a lightness L ^* value of 30 in the L ^* a ^* b ^* color system specified using a spectrophotometer (“CM-700d” manufactured by Konica Minolta) is used.

The first substrate 51 and the second substrate 52 are not limited to the illustrated example, and may include other functional layers expected to exhibit specific functions. One functional layer may exhibit two or more functions. Examples of functions that can be imparted to the first substrate 51 and the second substrate 52 include a scratch-resistant hard coat (HC) function, an infrared shielding (reflecting) function, an ultraviolet shielding (reflecting) function, an antifouling function, and the like. be.

The bonding layer 45 bonds the first substrate 51 and the second substrate 52 together. The bonding layer 45 is a transparent layer. As the bonding layer 45, a layer made of various materials having adhesiveness or cohesiveness may be used. As an example, the material of the bonding layer 45 may be a thermoplastic resin. The bonding layer 45 made of thermoplastic resin bonds to the first substrate 51 and the second substrate 52 by being heated and pressurized between the first substrate 51 and the second substrate 52 . Polyvinyl butyral (PVB) may be used as the thermoplastic resin forming the bonding layer 45 . The thickness of the bonding layer 45 in the normal direction ND is, for example, 20 μm or more and 1000 μm or less. The bonding layer 45 may be given various functions. Examples of various functions include an antistatic function and an ultraviolet absorption function.

The hologram element 60 diffracts the image light and directs it to the user 5 . Hologram element 60 may be transparent to provide transparency to combiner 40 . Hologram element 60 may have a high visible light transmittance. The hologram element 60 is sheet-like.

In the present embodiment, the hologram element 60 diffracts the image light incident on the combiner 40 in the specular reflection direction or in a direction inclined at an angle of 25° or less to the specular reflection direction. That is, as shown in FIG. 2, the magnitude of the difference between the incident angle θ1 to the hologram element 60 and the diffraction angle θ2 at the hologram element 60 is 25° or less. The difference between the incident angle θ1 and the diffraction angle θ2 may be 20° or less, 15° or less, 10° or less, 5° or less, or 3° or less. By setting an upper limit on the magnitude of the difference between the incident angle θ1 to the hologram element 60 and the diffraction angle θ2 at the hologram element 60, the noise image 91, which will be described later, is made inconspicuous, and discomfort when observing the noise image 91. can be suppressed.

The incident angle is the angle (°) formed by the traveling direction of the incident light before entering the incident target, that is, the incident direction, with respect to the normal direction to the incident target, and is less than 90°. In the illustrated example, the incident angle θ1 of the light L31 is the angle (°) between the incident direction to the combiner 40 and the normal direction ND. The diffraction angle is the angle (°) formed by the traveling direction of the diffracted light after being emitted from the diffraction target, that is, the diffraction direction, with respect to the normal direction to the diffraction target, and is less than 90°. In the illustrated example, the diffraction angle θ2 is the angle (°) between the output direction of the light L32 from the combiner 40 and the normal direction ND. Incident angle θ 1 and diffraction angle θ 2 are specified on a plane including incident light L 31 , diffracted light L 32 , and normal direction ND to hologram element 60 .

It should be noted that the incident angle and the reflection angle may change depending on the incident position on the combiner 40 and the like. The incident direction when measuring the incident angle is determined by the optical path having the highest intensity among the optical paths toward the center (center of gravity) of the area of the hologram element 60 where the image light from the projection device 25 can enter. , is specified. The emission direction for measuring the diffracted light and the reflected light is the highest of the optical paths emitted from the center (center of gravity) of the region of the hologram element 60 where the image light from the image forming apparatus 30 can enter. It is specified by the optical path of intensity.

The hologram element 60 includes a hologram recording layer 62 . The hologram recording layer 62 is a reflective hologram. The hologram recording layer 62 diffracts light of a specific wavelength incident from a specific incident direction with high diffraction efficiency and directs it in a specific direction. The hologram recording layer 62 records interference fringes for realizing a diffraction function. The hologram recording layer 62 diffracts incident light that satisfies the Bragg condition with high diffraction efficiency and directs it in a specific direction. The hologram recording layer 62 diffracts the image light from the image forming device 30 with high efficiency. The image forming device 30 is arranged at a predetermined position with respect to the combiner 40 so that the image light satisfies the Bragg condition of the hologram recording layer 62 . The hologram recording layer 62 diffracts the image light toward a predetermined direction with respect to the combiner 40 .

In the example shown in FIG. 2, the hologram recording layer 62 highly efficiently diffracts the image light that travels in the direction orthogonal to the first direction D1 and enters the hologram element 60 at the incident angle θ1 (°). The hologram recording layer 62 diffracts the image light with high efficiency in a direction orthogonal to the first direction D1 and having a diffraction angle of θ2 (°).

Information about the interference fringes can be recorded in the hologram recording layer 62 in various forms. The hologram recording layer 62 may be a phase-type hologram or an amplitude-type hologram. The hologram recording layer 62 may be a surface relief hologram, or may be a surface relief hologram as a computer generated hologram (CGH). The hologram recording layer 62 may be a volume hologram in that it is easy to increase the area. The hologram recording layer 62 may be a reflective volume hologram with sharp wavelength selectivity and angle selectivity.

FIG. 4 shows a method of exposing the photosensitive material layer 63 when creating a reflective volume hologram. Examples of the photosensitive material layer 63, which is the raw material of the hologram recording layer 62, include layers such as silver salt sensitive material, gelatin dichromate, crosslinkable polymer, and photopolymer. The thickness of the photosensitive material layer 63 and the obtained hologram recording layer 62 along the normal direction ND may be 1 μm or more and 100 μm or less, or may be 5 μm or more and 40 μm or less.

Coherent light emitted from a single light source is split into reference light L4A and object light L4B. The reference light L4A is shaped into divergent light by the lens 71 for reference light. The photosensitive material layer 63 is irradiated with the shaped reference light L4A. The incident direction of the reference light L4A to the photosensitive material layer 63 matches the incident direction of the image light to the hologram element 60 shown in FIG. The object light L4B is shaped into divergent light by the lens 72 for object light. The photosensitive material layer 63 is irradiated with the shaped object light L4B. Different surfaces of the photosensitive material layer 63 are irradiated with the object light L4B and the reference light L4A. An interference pattern is generated on the photosensitive material layer 63 by the object light L4B and the reference light L4A interfering with each other. The interference pattern is recorded as interference fringes in the photosensitive material layer 63 . In the photosensitive material layer 63 using a crosslinkable polymer, interference fringes are recorded as a pattern of refractive index change. The hologram recording layer 62 is obtained by desensitizing the photosensitive material layer 63 in which the interference fringes are recorded by exposing the entire surface.

The produced hologram recording layer 62 diffracts the illumination light L3A incident from the same direction as the reference light L4A with high diffraction efficiency. That is, the illumination light L3A incident from the same direction as the reference light L4A can satisfy the Bragg condition for the hologram recording layer 62. FIG. By matching or corresponding the optical path of the reference light L4A with the optical path of the image light, the hologram recording layer 62 can be given the desired angle dependency. The reproduction light L3B diffracted by the fabricated hologram recording layer 62 travels along the optical path of the object light L4B that has passed through the photosensitive material layer 63. FIG. By matching or corresponding the optical path of the object light L4B from the combiner 40 to the user 5, the hologram recording layer 62 can be given a desired angle dependency.

The produced hologram recording layer 62 diffracts light of the same wavelength as the reference light L4A and the object light L4B with high efficiency. That is, light having the same wavelength as the reference light L4A and the object light L4B can satisfy the Bragg condition of the hologram recording layer 62. FIG. Desired wavelength dependence can be imparted to the hologram recording layer 62 by matching or corresponding the wavelengths of the reference light L4A and the object light L4B to the center wavelength of the image light. When the image light is blue light, a laser beam with a wavelength of 430 nm or more and 490 nm or less may be used for exposure of the photosensitive material layer 63 . When the image light is green light, a laser beam with a wavelength of 490 nm or more and 550 nm or less may be used for exposure of the photosensitive material layer 63 . When the image light is red light, a laser beam with a wavelength of 600 nm or more and 660 nm or less may be used for exposure of the photosensitive material layer 63 .

The hologram element 60 may include multiple hologram recording layers 62 . The plurality of hologram recording layers 62 can diffract light of different wavelengths with high efficiency. For example, image light from projection device 25 may include blue light, green light, and red light. In this example, the hologram element 60 includes a hologram recording layer 62 that diffracts blue light with high efficiency, a hologram recording layer 62 that diffracts green light with high efficiency, and a hologram recording layer that diffracts red light with high efficiency. 62 may be included. When the hologram recording layer 62 is a volume hologram, the single hologram recording layer 62 may efficiently diffract light in a plurality of wavelength bands by multiple recording.

In the example shown in FIG. 2, the hologram element 60 includes a hologram recording layer 62 and a first sheet 64 and a second sheet 66 stacked in the normal direction ND. Hologram recording layer 62 is located between first sheet 64 and second sheet 66 . In the illustrated example, hologram recording layer 62 is bonded to first sheet 64 and second sheet 66 .

The first sheet 64 and the second sheet 66 function as base materials that support the hologram recording layer 62 . The first sheet 64 and the second sheet 66 function as protective layers that protect the hologram recording layer 62 . The first sheet 64 and the second sheet 66 are transparent sheets. Examples of materials for the first sheet 64 and the second sheet 66 include polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polystyrene, cyclic polyolefin, and the like. The thickness along the normal direction ND of the first sheet 64 and the second sheet 66 may be 10 μm or more and 100 μm or less. The first sheet 64 and the second sheet 66 may be identically constructed of the same material, may be constructed of different materials, or may have different constructions. Hologram element 60 may include one of first sheet 64 and second sheet 66 . Hologram element 60 may not include both first sheet 64 and second sheet 66 .

FIG. 5 shows an example of the spectral transmittance of the hologram element 60. FIG. That is, FIG. 5 shows the transmittance of the hologram element 60 for each wavelength. In the spectral transmittance of FIG. 5, the transmittance is lowered at wavelengths λ1, λ2, and λ3. Light corresponding to the drop in transmittance is diffracted by the hologram element 60 . That is, wavelength λ 1 , wavelength λ 2 and wavelength λ 3 are the centers of the selected wavelengths of hologram element 60 . A hologram element 60 having the optical properties shown in FIG. 5 may include three hologram recording layers 62 fabricated using the exposure method of FIG. The three hologram recording layers 62 use, as reference light L4A and object light L4B, light of three different wavelengths λ1, λ2, and λ3 corresponding to the minimum values of the spectral transmittance shown in FIG. can be made.

From the viewpoint of making the noise image 91 described later inconspicuous, it is preferable to set an upper limit on the diffraction efficiency of the hologram element 60 . The diffraction efficiency of the hologram element 60 may be 60% or less, 40% or less, or 20% or less. When light of a plurality of wavelengths is used when exposing the hologram recording layer 62, the hologram element 60 has a peak value of diffraction efficiency for the light of the plurality of wavelengths. For example, light with a wavelength of 460 nm, light with a wavelength of 532 nm, and light with a wavelength of 640 nm can be used to expose the photosensitive material layer 63 . When the hologram element 60 has diffraction efficiency peak values for light of a plurality of wavelengths, the "diffraction efficiency of the hologram element 60" means the maximum value of diffraction efficiency for light of each wavelength.

The diffraction efficiency of the hologram element 60 is measured by any one appropriate measurement method conforming to JISZ8791:2011. The diffraction efficiency (%) of the hologram element 60 means the maximum ratio of the radiant flux (watts) of the first-order diffracted light to the radiant flux (watts; W) of the illumination light to the hologram element 60 . Therefore, the radiant flux (watts) of the first-order diffracted light is measured while the hologram element 60 is irradiated with the illumination light satisfying the Bragg condition. Specifically, the optical axis of the illumination light L3A with respect to the hologram element 60 is aligned with the optical axis of the reference light L4A with respect to the photosensitive material layer 63 during exposure. The radiant flux (watts) of the first-order diffracted light can be specified by measuring the radiant flux of the diffracted light emitted from the hologram element 60 in a direction parallel to the optical path of the object light L4B during exposure. The optical axis is identified as the optical path of highest intensity.

From the viewpoint of making the noise image 91 described later inconspicuous, it is preferable to set an upper limit to the full width at half maximum (nm) in the wavelength distribution of the diffraction efficiency of the hologram element 60 . The full width at half maximum (nm) in the wavelength distribution of the diffraction efficiency of the hologram element 60 may be 20 nm or less, 10 nm or less, or 5 nm or less. The full width at half maximum means an interval (nm) between two wavelengths located on both sides of a wavelength at which a peak value of diffraction efficiency is obtained and at which half of the peak value of diffraction efficiency is ensured. When the hologram element 60 has diffraction efficiency peak values for light of a plurality of wavelengths, the “full width at half maximum (nm) in the wavelength distribution of the diffraction efficiency of the hologram element 60” is the maximum value of the full width at half maximum for light of each wavelength. means

Next, the action of the illustrated head-up display 20 will be described.

As shown in FIG. 6, image light L61 is emitted from the projection device 25. Image light L<b>61 is formed by image forming device 30 and directed to combiner 40 by projection optics 35 . The image light L61 enters the combiner 40 from the first surface 41 . The image light L61 enters the hologram element 60 of the combiner 40 as illumination light L62. The hologram recording layer 62 of the hologram element 60 diffracts the image light L61 as the illumination light L62 with high efficiency. The image light L61 diffracted by the hologram element 60 is reflected by the hologram element 60 toward the user 5 as reproduction light L63. The user 5 can observe the image formed by the image light L61. The user 5 observes the image not at the position of the image forming apparatus 30 but at a position behind the combiner 40 along the direction parallel to the optical path of the reproduction light L63. That is, according to the head-up display 20, the virtual image 80 observed by the user 5 can be displayed behind the combiner 40 with the user 5 as a reference.

In the illustrated head-up display 20, the position where the virtual image 80 is displayed can be adjusted by the hologram element 60. By adjusting the distance DY from the object light lens 72 to the photosensitive material layer 63 with respect to the distance DX from the reference light lens 71 to the photosensitive material layer 63 shown in FIG. You can adjust the position and size. Specifically, the virtual image 80 can be displayed farther from the user 5 and the combiner 40 by increasing the ratio of the distance DY to the distance DX (DY/DX). The size of the virtual image 80 can be increased by increasing the ratio of the distance DY to the distance DX (DY/DX).

By the way, when a conventional head-up display is used in a place where the sun, outdoor lights, etc. are installed, the external light source 90 may be reflected in the combiner 140 as an unintended noise image 91 . Here, the external light source is a light source provided in the installation environment of the head-up display, such as the sun or an outdoor lamp. An external light source is a light source that emits light that is not intended to enter the combiner. As an external light source, a light source that emits environmental light such as the sun or an outdoor light is exemplified. Moreover, the noise image 91 of the sun, an outdoor lamp, etc. is observed at a position different from the actual position of the external light source 90, such as the sun or an outdoor lamp. The appearance of such a noise image 91 degrades the display quality of the head-up display 120 and reduces visibility through the combiner 140 .

The appearance of the noise image 91 is considered to be due to the following reasons. As shown in FIG. 11, the noise light L112 from the external light source 90 enters the combiner 140 via the second surface 142 unlike the image light L111. The noise light L112 reaches the first surface 141 and is reflected by the first surface 141 . After that, noise light L112 enters hologram element 160 . When the optical path of the noise light L112 satisfies the Bragg diffraction condition of the hologram recording layer 162, the noise light L112 is diffracted by the hologram recording layer 162 with high efficiency and travels toward the user 5. User 5 observes noise image 91 located behind combiner 140 .

On the other hand, in the present embodiment, the hologram element 60 diffracts the image light in the specular reflection direction with respect to the incident direction of the image light to the combiner 40 or in a direction inclined at an angle of 25° or less to the specular reflection direction. That is, the hologram element 60 diffracts the image light L61 in a direction that is not greatly inclined with respect to the regular reflection direction with respect to the incident direction of the image light L61 to the combiner 40 .

In the example shown in FIG. 7, the hologram element 60 diffracts incident light that satisfies the Bragg condition in the specular direction. In this example, the noise light L71 emitted from the external light source 90 passes through the second surface 42 and enters the combiner 40 . The noise light L71 then travels through the combiner 40 toward the first surface 41 . The noise light L71 is specularly reflected by the first surface 41 . That is, the incident angle θa of the noise light L71 to the first surface 41 is the same as the reflection angle θb of the reflected light L72 reflected by the first surface 41 . The angle of reflection is the angle (°) formed by the traveling direction of the reflected light with respect to the normal direction to the object to be reflected, and is less than 90°.

The noise light L72 reflected by the first surface 41 then travels toward the hologram element 60. In the example shown in FIG. 7, the noise light L72 travels in a direction parallel to the image light L74 and enters the hologram element 60. In the example shown in FIG. Therefore, the noise light L72 satisfies the Bragg condition of the hologram recording layer 62 of the hologram element 60 and is diffracted by the hologram recording layer 62 with high efficiency. Due to the diffraction at the hologram recording layer 62, the noise light L72 is diffracted at the hologram recording layer 62 in the regular reflection direction. The diffracted light L73 reflected by the hologram element 60 is emitted from the combiner 40 toward the user 5. FIG.

The incident angle θc of the noise light L72 to the hologram element 60 is the same as the reflection angle θb of the reflected light L72 reflected by the first surface 41 . Also, the incident angle θc of the noise light L72 to the hologram element 60 is the same as the diffraction angle θd of the diffracted light L73 reflected and diffracted by the hologram element 60 . As a result, the noise light L73 directed toward the user 5 travels in a direction parallel to the noise light L71 emitted from the external light source 90 . The thickness of the combiner 40 in the normal direction ND is sufficiently thin with respect to the distance from the combiner 40 to the external light source 90 and the size of the external light source 90 . Therefore, the user 5 observes a noise image 91 of the external light source 90 at a position overlapping the external light source 90 . That is, the real image of the external light source 90 that can be observed through the combiner 40 and the noise image 91 of the external light source 90 are at least partially overlapped and observed. Therefore, it is possible to greatly reduce the sense of incongruity when the user 5 observes the noise image 91 . Furthermore, it is assumed that the user 5 does not notice the noise image 91 . Thereby, the display quality of the head-up display 20 is improved, and the visibility through the combiner 40 is improved.

Unlike the illustrated example, the hologram element 60 may diffract the image light in a direction inclined at an angle of 25° or less in the regular reflection direction with respect to the incident direction of the image light to the combiner 40 . The traveling direction of the noise light L73 toward the user 5 can be inclined by an angle of 25° or less with respect to the traveling direction of the noise light L71 emitted from the external light source 90 . This example also allows the user 5 to observe the noise image 91 of the external light source 90 at a position at least partially overlapping the external light source 90 . That is, the real image of the external light source 90 that can be observed through the combiner 40 and the noise image 91 of the external light source 90 overlap each other, making it difficult to distinguish them from each other. For this reason, it is possible to greatly suppress discomfort when the user 5 observes the noise image 91 . Furthermore, it is assumed that the user 5 does not notice the noise image 91 . Thereby, the display quality of the head-up display 20 is improved, and the visibility through the combiner 40 is improved.

Thus, by setting an upper limit on the difference between the angle of incidence θ1 of the combiner 40 on the hologram element 60 and the angle of diffraction θ2 of the combiner 40 at the hologram element 60, the noise image 91 is observed when the noise image 91 is observed. Discomfort can be suppressed. The difference between the incident angle θ1 and the diffraction angle θ2 may be 25° or less, 20° or less, 15° or less, 10° or less, 5° or less, or 3° or less.

As described above, according to the embodiment in which the hologram element 60 diffracts the image light in the specular reflection direction with respect to the incident direction of the image light to the combiner 40 or in a direction inclined at an angle of 25° or less to the specular reflection direction, noise The image 91 can be made inconspicuous. However, when the hologram element 60 having this diffraction characteristic is used, a new problem described below may occur.

As shown in FIG. 6, part of the image light L61 can be specularly reflected by the first surface 41. Also, part of the image light L61 may be specularly reflected by the second surface 42 . These reflected lights L64 travel in a direction parallel or substantially parallel to the light diffracted by the hologram element 60. FIG. That is, the reflected light L64 is also reflected toward the user 5. FIG. Therefore, the user 5 observes the ghost image 81 of the image by the reflected light L64 reflected by the

surfaces

41 and 42 of the combiner 40. FIG. As shown in FIGS. 2 and 6, the ghost image 81 not intended for display is viewed in the same direction as the virtual image 80 of the image intended for display. Overlapping of the ghost image 81 with the virtual image 80 may cause a problem that the visibility of the virtual image 80 intended to be displayed is reduced.

To deal with this new problem, in the present embodiment, as shown in FIG. The distance LY between the image by the image light L64 reflected by the first surface 41 or the second surface 42, that is, the display position PX of the ghost image 81 and the hologram element 60 is four times or more. The distance LX may be 6 times or more the distance LY, the distance LX may be 8 times or more the distance LY, the distance LX may be 12 times or more the distance LY, or the distance LX may be 16 times or more the distance LY. good. Also, the difference between the distance LX and the distance LY may be 1 m or more, 2 m or more, 4 m or more, or 8 m or more. When the distance LX and the distance LY are adjusted in this way, the display position PX of the virtual image 80 is sufficiently separated from the display position PY of the ghost image 81 . Therefore, when changing the observation target from the ghost image 81 to the virtual image 80, the user 5 needs to change the focus position of the eye. That is, it is possible to prevent the ghost image 81 from being clearly observed together with the virtual image 80 . Accordingly, it is possible to prevent the visibility of the virtual image 80 from being impaired by the ghost image 81 .

As described above, in order to make the noise image 91 inconspicuous, it is effective to reduce the reflectance of the antireflection layer 57 forming the first surface 41 . By reducing the reflectance of the antireflection layer 57, the radiant flux (W) of the noise light L72 incident on the hologram element 60 can be reduced. In addition, the antireflection layer 57 can also suppress reflection of the image light L61 on the surface of the combiner 40 . Thereby, the ghost image 81 can be made inconspicuous. Specifically, the reflectance of the antireflection layer 57 may be 1% or less, or 0.5% or less. The reflectance (%) of the antireflection layer 57 can be adjusted by the thickness of the antireflection layer 57, the number of layers included in the antireflection layer 57, the refractive index of the material forming the antireflection layer 57, and the like.

Furthermore, reducing the diffraction efficiency of the hologram element 60 is effective in making the noise image 91 inconspicuous. By reducing the diffraction efficiency of the hologram element 60, the noise image 91 can be darkened. Specifically, the diffraction efficiency of the hologram element 60 may be 60% or less, 40% or less, or 20% or less.

Furthermore, in order to make the noise image 91 inconspicuous, it is effective to reduce the full width at half maximum W (nm) in the wavelength distribution of the diffraction efficiency of the hologram element 60 . The noise image 91 can be darkened by reducing the full width at half maximum W (nm) in the wavelength distribution of the diffraction efficiency of the hologram element 60 . Specifically, the full width at half maximum W (nm) in the wavelength distribution of the diffraction efficiency of the hologram element 60 may be 20 nm or less, 10 nm or less, or 5 nm or less.

The diffraction efficiency (%) of the hologram element 60 and the full width at half maximum (nm) in the wavelength distribution of the diffraction efficiency of the hologram element 60 can be adjusted by changing the manufacturing conditions of the hologram element 60 . For example, the diffraction efficiency (%) and The full width at half maximum (nm) is adjustable. The diffraction efficiency (%) and the full width at half maximum (nm) can be adjusted also by the intensity of the exposure light and the exposure time when the photosensitive material layer 63 is exposed.

Here, an example of an experiment conducted by the inventors will be explained.

Samples 1 to 5 of the combiner 40 shown in FIG. 8 were produced. Combiners 40 of samples 1-5 included first substrate 51 , second substrate 52 , bonding layer 45 , and hologram element 60 . Hologram element 60 included first sheet 64 , hologram recording layer 62 and second sheet 66 . The combiner 40 according to Samples 1 to 5 was laminated glass in which the hologram element 60 was arranged in the bonding layer 45 .

The first substrate 51 and the second substrate 52 had a square shape of 150 mm×150 mm when observed from the normal direction ND. The hologram element 60 had a square shape of 100 mm×100 mm when observed from the normal direction ND. The hologram element 60 was arranged with respect to the first substrate 51 and the second substrate 52 so that the periphery of the hologram element 60 was located 25 mm inside from the periphery of the first substrate 51 and the second substrate 52 .

<Sample 1>
In sample 1, the thickness T1 along the normal direction ND of the first substrate 51 was set to 2 mm. The thickness T2 along the normal direction ND of the second substrate 52 was set to 2 mm. Soda plate glass was used as the second substrate 52 . Polyvinyl butyral (PVB) was used as the bonding layer 45 . A thickness T3 of the bonding layer 45 between the hologram element 60 and the first substrate 51 was set to 380 μm. A thickness T3 of the bonding layer 45 between the hologram element 60 and the second substrate 52 was set to 380 μm.

The hologram element 60 included a single hologram recording layer 62 . The hologram recording layer 62 is a reflective volume hologram. This single hologram recording layer 62 had wavelength selectivity with respect to blue wavelength (460 nm) light, green wavelength (532 nm) light, and red wavelength (640 nm) light by multiple exposure. . That is, the blue wavelength light, the green wavelength light, and the red wavelength light each satisfied the Bragg condition for the single hologram recording layer 62 . The hologram recording layer 62 was produced under the exposure conditions shown in FIG. 4 using blue wavelength light, green wavelength light, and red wavelength light. The hologram element 60 was made to satisfy the Bragg condition with light incident at an incident angle of 56°. The hologram element 60 was made to have a diffraction characteristic of reflecting light incident at an incident angle of 56° in the regular reflection direction.

The hologram recording layer 62 was produced using a crosslinkable polymer. The thickness T6 of the hologram recording layer 62 was 15 μm. The first sheet 64 and the second sheet 66 were polyethylene terephthalate sheets. The thickness T7 of the first sheet 64 was 50 μm. The thickness T8 of the second sheet 66 was 38 μm.

<Sample 2>
Sample 2 differed from Sample 1 in the diffraction characteristics of the hologram element. Sample 2 was otherwise similar to Sample 1.

In Sample 2, the manufacturing method of the hologram recording layer 62 was the same as the manufacturing method of the hologram recording layer 62 in Sample 1, except for the incident direction of the object light. The hologram element 60 was made so that the Bragg condition was satisfied by light incident at an incident angle of 54°. The hologram element 60 was made to have a diffraction characteristic of reflecting light incident at an incident angle of 54° in a direction inclined by 10° with respect to the regular reflection direction.

<Sample 3>
Sample 3 differed from samples 1 and 2 in the diffraction properties of the hologram element. Sample 3 was otherwise similar to Samples 1 and 2.

In sample 3, the method of manufacturing the hologram recording layer 62 was the same as the method of manufacturing the hologram recording layer 62 in sample 1, except for the incident direction of the object light. The hologram element 60 was made to satisfy the Bragg condition with light incident at an incident angle of 52°. The hologram element 60 was made to have a diffraction characteristic of reflecting light incident at an incident angle of 52° in a direction inclined by 20° with respect to the regular reflection direction.

<Sample 4>
Sample 4 differed from Samples 1 to 3 in the diffraction characteristics of the hologram element. Sample 4 was otherwise similar to Samples 1-3.

In sample 4, the method of manufacturing the hologram recording layer 62 was the same as the method of manufacturing the hologram recording layer 62 in sample 1, except for the incident direction of the object light. The hologram element 60 was made to satisfy the Bragg condition with light incident at an incident angle of 56°. The hologram element 60 was made to have a diffraction characteristic of reflecting light incident at an incident angle of 56° in a direction inclined by 25° with respect to the regular reflection direction.

<Sample 5>
Sample 5 differed from Samples 1 to 4 in the diffraction characteristics of the hologram element. Sample 5 was otherwise similar to Samples 1-4.

In sample 5, the method of manufacturing the hologram recording layer 62 was the same as the method of manufacturing the hologram recording layer 62 in sample 1, except for the incident direction of the object light. The hologram element 60 was made to satisfy the Bragg condition with light incident at an incident angle of 56°. The hologram element 60 was made to have a diffraction characteristic of reflecting light incident at an incident angle of 56° in a direction inclined by 30° with respect to the specular reflection direction.

<Evaluation 1>
Samples 1-5 were placed on the windshield of an actual automobile. A noise image 91 of an external light source 90 was observed in the combiner 40 of samples 1-5 by adjusting the position and orientation of the automobile. The external light source 90 was an outdoor lamp. In sample 1, the noise image 91 was mostly observed overlapping the real image of the external light source 90, and was not noticeable. In samples 2 to 4, the noise image 91 was not large and conspicuous, and the noise image 91 did not distract attention. In sample 5, the noise image 91 was observed at a position greatly deviated from the real image of the external light source 90, and felt uncomfortable. In addition, the size of the noise image 91 observed was the largest in sample 5 and the smallest in sample 1. FIG. The color of the noise image 91 of sample 5 was significantly different from the color of the external light source 90, and was partially rainbow colored.

<Evaluation 2>
A head-up display 20 was produced by combining Samples 1 to 5 with a projection device 25 . As the projection device 25, a commercially available projection device for the head-up display 20 was used. The projection device 25 was common among the samples 1-5. A virtual image 80 of an image displayed by the head-up display 20 and a ghost image 81 were observed. In any of Samples 1 to 5, the display position PX of virtual image 80 was 2 m away from combiner 40 . In all samples 1 to 5, the display position PY of the ghost image 81 was 50 cm away from the combiner 40 . In the head-up display 20 using any of Samples 1 to 5, the virtual image 80 could be observed without the ghost image 81 being conscious. That is, the ghost image 81 did not deteriorate the visibility of the virtual image 80 . In order to carefully observe the ghost image 81, it was necessary to stop observing the virtual image 80 and adjust the focus position.

In the embodiment described above, the combiner 40 projects image light used for the head-up display 20 . The combiner 40 includes a first substrate 51 including a first surface 41 that serves as an incident surface for image light, a second substrate 52 including a second surface 42, and a bonding layer 45 that bonds the first substrate 51 and the second substrate 52 together. and a hologram element 60 positioned between the first substrate 51 and the second substrate 52 .

In one embodiment, the hologram element 60 may diffract the image light in a specular reflection direction with respect to the incident direction of the image light to the combiner 40 or in a direction inclined at an angle of 25° or less to the specular reflection direction. Also, the external light source 90 is observed by the light emitted from the external light source 90 , incident on the combiner 40 from the second surface 42 , reflected by the first surface 41 , diffracted by the hologram element 60 , and emitted from the first surface 41 . may at least partially overlap the real image of the external light source 90 viewed through the combiner 40 . According to this combiner 40, the real image of the external light source 90 and the noise image 91 are hardly distinguished from each other, and the noise image 91 can be made inconspicuous. Therefore, the display quality of the head-up display 20 can be improved, and the visibility through the combiner 40 can be improved.

According to one embodiment, the noise image 91 can be made inconspicuous, but new problems may arise. That is, a ghost image 81 not intended for display can be observed in the same direction as the virtual image 80 of the image intended for display. At this time, ghost image 81 overlaps virtual image 80, which may reduce the visibility of virtual image 80 intended to be displayed. In order to deal with this problem, in one embodiment, the distance LX between the display position PX of the image (virtual image) 80 by the image light diffracted by the hologram element 60 and the hologram element 60 is adjusted to the first surface 41 or the second surface. It may be four times or more the distance LB between the display position PB of the image 81 by the image light reflected by 42 and the hologram element 60 . When the distance LX and the distance LY are adjusted in this way, the display position PX of the virtual image 80 is greatly separated from the display position PY of the ghost image 81 . Therefore, when changing the observation target from the ghost image 81 to the virtual image 80, the user 5 needs to change the focus position of the eye. That is, it is possible to prevent the ghost image 81 from being clearly observed together with the virtual image 80 . Also, the ghost image 81 is sufficiently small compared to the virtual image 80 that is enlarged and projected. These can prevent the ghost image 81 from impairing the visibility of the virtual image 80 . The display quality of the head-up display 20 is improved.

In a specific example of one embodiment, the first substrate 51 may include an antireflection layer 57 forming the first surface 41 . The antireflection layer 57 can make unintended noise images 91 and ghost images 81 inconspicuous.

Although one embodiment has been described with reference to specific examples, the above specific examples do not limit one embodiment. The embodiment described above can be implemented in various other specific examples, and various omissions, replacements, changes, additions, etc. can be made without departing from the scope of the invention. For example, the second substrate 52 may include an antireflection layer forming the second surface 42 .

Further examples of deformation will be described below with reference to the drawings. In the following description and the drawings used in the following description, the same reference numerals as those used for the corresponding portions in the above-described specific example are used for portions that can be configured in the same manner as in the above-described specific example, and redundant description is omitted. omitted.

As shown in FIG. 9, the hologram element 60 may diffract the image light in a direction inclined with respect to the specular reflection direction with respect to the incident direction of the image light to the combiner 40 . FIG. 9 shows the incident angle θ1 of the image light L91 to the combiner 40 and the hologram element 60, the diffraction angle θ2 of the image light L91 at the hologram element 60, and the reflection angle θ3 of the image light L91 at the combiner 40. . Light L92 shown in FIG. 9 is the optical path of reflected light specularly reflected by the first surface 41 or the second surface 42 of the combiner 40 . The angle of incidence θ1 and the angle of reflection θ3 are equal. The diffraction angle θ2 is different from the incident angle θ1 and the reflection angle θ3. Therefore, the direction in which the user 5 observes the virtual image 80 is non-parallel to the direction in which the user 5 observes the ghost image 81 . According to this example, the virtual image 80 can be displayed by being shifted from the ghost image 81 . Therefore, it becomes easier for the user 5 to distinguish between the virtual image 80 and the ghost image 81 . That is, the visibility of the virtual image 80 can be improved.

When the difference between the incident angle θ1 of the image light L111 on the hologram element 60 and the diffraction angle θ2 of the image light L111 on the hologram element 60 is large, the virtual image 80 can be easily distinguished from the ghost image 81 and visually recognized. Therefore, by increasing the difference between the incident angle θ1 of the combiner 40 to the hologram element 60 and the diffraction angle θ2 of the combiner 40 at the hologram element 60, that is, by increasing the angle θ4 in FIG. 9, the visibility of the virtual image 80 is further improved. can. The difference θ4 between the incident angle θ1 to the combiner 40 and the diffraction angle θ2 at the combiner 40 may be 3° or more, 5° or more, or 10° or more. This setting can sufficiently improve the visibility of the virtual image 80 .

Note that in the example shown in FIG. 9, the incident direction and the diffraction direction of the image light are inclined to different sides with respect to the normal direction ND. In this example, the magnitude of the diffraction angle θ2 may be smaller than the magnitude of the incident angle θ1. That is, the diffraction angle θ2 may be smaller than the reflection angle θ3. According to this example, the user 5 observes the ghost image 81 due to the reflected light L92 below the virtual image 80 due to the diffracted light in the vertical direction. In the head-up display 20 using the front window 14 of the automobile 12, the ghost image 81 is observed at a position closer to the dashboard than the virtual image 80 is. The ghost image 81 becomes less likely to enter the field of view of the user 5 . That is, by making the magnitude of the diffracted light θ2 smaller than the magnitude of the incident angle θ1, the ghost image 81 can be made inconspicuous and the virtual image 80 can be easily observed.

As shown in FIG. 9, the image light L92 reflected by the first surface 41 or the second surface 42 of the combiner 40 and directed toward the user 5 is horizontally (in the illustrated example, the second direction D2) It may proceed in an upwardly sloping direction. According to this example, as shown in FIG. 13, the user 5 observes the ghost image 81 in a direction tilted downward from the horizontal direction. In the head-up display 20 using the front window 14 of the automobile 12, a ghost image 81 is observed overlapping the hood or at a position close to the hood. Therefore, it becomes easy to distinguish the virtual image 80 from the ghost image 81 and observe it.

In the example shown in FIG. 7, the magnitude of the incident angle .theta.1 of the image light is larger than the magnitude of the tilt angle .theta.5 of the combiner 40. In the example shown in FIG. According to such a configuration, the magnitude of the diffracted light θ2 tends to be smaller than the magnitude of the incident angle θ1. According to such a configuration, the reflected light L92 of the image light reflected by the first surface 41 or the second surface 42 of the combiner 40 tends to travel in a direction inclined upward with respect to the horizontal direction. Here, the tilt angle θ5 (°) of the combiner 40 is the magnitude of the angle formed by the normal direction ND of the combiner 40 with respect to the vertical direction (the third direction D3 in the illustrated example), and is less than 90°. is the value of The tilt angle θ5 (°) of the combiner 40 is specified as the tilt angle at the central position (gravity center position) of the region of the hologram element 60 where the image light can enter. The incident angle θ1 (°), the diffraction angle θ2 (°), and the reflection angle θ3 (°) of the image light are, as already explained, at the center position (center of gravity) of the region of the hologram element 60 where the image light can enter. It is specified by the optical path of the incident image light.

Furthermore, the optical path length Lz of the image light L91 from the projection device 25 to the combiner 40 may be lengthened. As shown in FIG. 9 , the optical path length Lz is the optical path length of image light from the projection device 25 to the combiner 40 . More precisely, Lz is the output end 25a of the projection device 25 for the image light traveling to the center position (center of gravity) of the region on which the image light is incident on the hologram element 60, that is, from the most light-emitting surface of the projection device 25 to the combiner 40. is the optical path length to In the example shown in FIG. 9, the optical path length Lz is lengthened from the position of the first projection device 25A to the position of the second projection device 25B. When the optical path length Lz of the image light L91 from the projection device 25 to the combiner 40 is lengthened in this way, the position where the ghost image 81 is observed moves from the first ghost image position PY1 to the second ghost image position PY2. and approaches the position where the virtual image 80 is observed. However, the direction in which the user 5 observes the ghost image 81 is inclined to the direction in which the user 5 observes the virtual image 80 . Therefore, overlapping of the ghost image 81 and the virtual image 80 is suppressed, and it becomes easy to distinguish the virtual image 80 from the ghost image 81 and visually recognize it.

The optical path length Lz of the image light L91 from the combiner 40 to the image forming apparatus 30 may be 200 mm or longer, 250 mm or longer, 300 mm or longer, 350 mm or longer, or 400 mm or longer. By setting in this way, the visibility of the virtual image 80 can be effectively improved in the head-up display 20 using the front window 14 of the automobile 12 shown in FIG.

Further, the value of the formula "Lz × sin θ4" using the optical path length Lz (mm) and the angle difference θ4 (°) may be 10 mm or more, 20 mm or more, 30 mm or more, or 40 mm or more. Well, it may be 50 mm or more. “Lz×sin θ4” is an index indicating how far the ghost image 81 is observed from the direction in which the virtual image 80 is observed. By adjusting the magnitude of the formula “Lz×sin θ4”, the visibility of the virtual image 80 can be effectively improved in the head-up display 20 using the front window 14 of the automobile 12 shown in FIG.

In the example shown in FIG. 9, the optical path length Lz of the image light L91 from the combiner 40 to the projection device 25 is linear. Unlike the example shown in FIG. 9, an optical element that changes the optical path of the image light L91, such as a reflecting mirror, may be installed between the combiner 40 and the projection device 25. FIG. By providing one or more optical elements for folding back the optical path of the image light L91, the optical path length Lz can be increased.

As shown in FIG. 13, when the diffraction angle θ2 is different from the incident angle θ1, the ghost image 81 due to specularly reflected light at the combiner 40 is observed in a different direction from the virtual image 80. The image light L131 displaying the virtual image 80 and the image light L132 displaying the ghost image 81 enter different regions of the combiner 40 . The image light L131 displaying the virtual image 80 enters the area of the combiner 40 where the hologram element 60 is located. At least a portion of the image light L132 displaying the virtual image 80 may enter a region of the combiner 40 where the hologram element 60 is not located. By restricting the incidence of the image light L132 to the combiner 40, the ghost image 81 can be made inconspicuous.

As shown in FIG. 13 , the head-up display 20 may include a light blocking member 32 that blocks part of the image light emitted from the image forming device 30 . The light shielding member 32 may be arranged so as to be shifted from the optical path of the image light L131 emitted from the image forming apparatus 30 and diffracted by the hologram element 60 of the combiner 40 . The light shielding member 32 is arranged outside the optical path of the image light L131. Therefore, the light blocking member 32 does not block the image light L131. Thereby, the virtual image 80 can be observed brightly. The light shielding member 32 is positioned outside the optical path of the image light L131 and absorbs the image light L132 that does not enter the hologram element 60 .

The light shielding member 32 has a visible light shielding property. The visible light shielding property means that the visible light transmittance is (numerical value) % or less, preferably (numerical value) % or less. As described above, the visible light transmittance is measured using a spectrophotometer ("UV-3100PC" manufactured by Shimadzu Corporation, compliant with JIS K0115) at a wavelength of 380 nm or more and 780 nm or less. It is specified as the average total light transmittance at each wavelength, measured in degrees. The visible light blocking property of the light blocking member 32 may be light absorption or light reflection.

The configuration of the light shielding member 32 is not particularly limited. The material of the light shielding member 32 may be metal with high reflectance. The material of the light shielding member 32 may contain absorptive pigments such as carbon black and titanium black. The shape of the light shielding member 32 is not particularly limited. The light shielding member 32 may be plate-shaped or box-shaped.

From the viewpoint of shielding the image light L132 that displays the ghost image 81 without shielding the image light L131 that displays the virtual image 80, the difference between the diffraction angle θ2 and the incident angle θ1 may be increased. The difference θ4 between the diffraction angle θ2 and the incident angle θ1 may be 3° or more, 5° or more, or 10° or more. From the viewpoint of shielding only the image light L132 that displays the ghost image 81, the optical path length Lz of the image light from the projection device 25 to the combiner 40 may be lengthened. From the viewpoint of shielding only the image light L132 that displays the ghost image 81, the size of the projection image projected from the image forming apparatus 30 onto the combiner 40 may be reduced. At this time, by adjusting the diffraction characteristics of the hologram recording layer 62, the magnification of the virtual image 80 with respect to the projected image can be increased, and a large virtual image 80 can be displayed.

The image light incident on the combiner 40 is diffused to some extent. Due to the diffusion of the image light, the virtual image 80 can be observed even if the observer's viewpoint position is shifted. On the other hand, when the image light becomes divergent light and enters the combiner 40, the ghost image 81 can be observed in a direction different from the virtual image 80 as described above. By controlling the divergence of the image light, the ghost image 81 is less likely to be observed. The head-up display 20 and the projection device 25 may include an optical path adjusting member 34 arranged between the image forming device 30 and the combiner 40 . The optical path adjusting member 34 may adjust the optical path of the image light. The optical path adjusting member 34 may have an anisotropic diffusion function. The optical path adjusting member 34 having an anisotropic diffusion function can suppress the generation of the ghost image 81 .

The optical path adjustment member 34 may suppress diffusion in each direction in the first evaluation plane P1 parallel to both the normal direction ND of the combiner 40 and the optical axis 95 of the image light directed toward the hologram element 60. The optical path adjusting member 34 has a stronger diffusing function in the second evaluation plane P2, which is perpendicular to the first evaluation plane P1 and parallel to the optical axis 95 of the image light directed to the hologram element 60, than in the first evaluation plane P1. may have.

The optical axis 95 of the image light directed to the hologram element 60 is the optical path having the highest intensity among the optical paths of the image light directed to the center (center of gravity) of the area of the hologram element 60 where the image light can enter. match. The paper plane of FIG. 13 is parallel to the first evaluation plane P1. In the example shown in FIG. 13, the second evaluation plane P2 is a plane that passes through the optical axis 95 and is orthogonal to the plane of FIG. In the example shown in FIG. 13, the second evaluation plane P2 is a plane parallel to both the optical axis 95 and the first direction D1.

The diffusion function of the optical path adjusting member 34 within the first evaluation plane P1 is evaluated based on the luminance distribution on the optical path adjusting member 34 in various directions along the first evaluation plane P1. The diffusion function of the optical path adjusting member 34 within the second evaluation plane P2 is evaluated based on the luminance distribution on the optical path adjusting member 34 in various directions along the second evaluation plane P2. When the full width at half maximum in the angular distribution of luminance is large, the diffusion function is strong, and when the full width at half maximum FWHM in the angular distribution of luminance is small, the diffusion function is weak. The angular distribution of luminance is measured using parallel light traveling in the normal direction to the light exit surface of the optical path adjusting member 34 as incident light. The full width at half maximum FWHM is an angular range (°) in which luminance equal to or greater than half the maximum luminance is obtained in the angular distribution of luminance. In the example shown in FIG. 14, the full width at half maximum FWHM2 at the second evaluation plane P2 is significantly larger than the full width at half maximum FWHM1 at the first evaluation plane P1. In the example shown in FIG. 14, the optical path adjustment member 34 has a stronger diffusion function within the second evaluation plane P2 than within the first evaluation plane P1.

The optical path adjusting member 34 having the anisotropic diffusion function is not particularly limited. 15 to 17 show specific examples of the optical path adjustment member 34. FIG.

As shown in FIG. 15, the optical path adjusting member 34 may include a lens sheet 36. The lens sheet 36 may be a lenticular lens. The lens sheet 36 includes a sheet-like body portion 36a and a plurality of unit lenses 36b supported by the body portion 36a. A plurality of unit lenses may constitute a linear array lens. A plurality of unit lenses 36b are arranged in the X direction DX. Each unit lens 36b may extend in a direction non-parallel to the X direction DX. The illustrated unit lens 36b extends linearly in the Y direction orthogonal to the X direction DX. The body portion 36 a may face the image forming apparatus 30 and the plurality of unit lenses 36 b may face the combiner 40 . The body portion 36 a may face the combiner 40 and the plurality of unit lenses 36 b may face the image forming apparatus 30 . The illustrated lens sheet 36 has a strong diffusion function in the X direction DX and a weak diffusion function in the Y direction DY. Therefore, the lens sheet 36 may be incorporated into the head-up display 20 so that the X direction DX crosses the first evaluation plane P1. The lens sheet 36 may be incorporated into the head-up display 20 so that the X direction DX is orthogonal to the first evaluation plane P1.

At least one of the body portion 36a and the unit lens 36b may contain a diffusion component. Examples of diffusion components include metal compounds, gas-containing porous substances, resin beads around which metal compounds are retained, white fine particles, and simple air bubbles. The lens sheet 36 shown in FIG. 15 may be used in combination with other optical sheets. As an optical sheet, a light diffusion sheet having an isotropic diffusion function is exemplified.

As shown in FIG. 16, the optical path adjustment member 34 may include a light control sheet 37. The light control sheet 37 is a so-called louver sheet in which a louver-shaped structure is formed inside the sheet. The light control sheet 37 includes absorption portions 37a and transmission portions 37b alternately arranged in the X direction DX. The absorbing portion 37a has visible light absorbing properties. The absorption part 37a may contain a pigment having visible light absorption properties. The transmissive portion 37b may be transparent. The absorbing portion 37a and the transmitting portion 37b may extend in a direction non-parallel to the X direction DX. The illustrated absorbing portion 37a and transmitting portion 37b linearly extend in the Y direction orthogonal to the X direction DX. The illustrated light control sheet 37 includes a sheet-like base portion 37c. The base portion 37c supports the absorbing portion 37a and the transmitting portion 37b from the Z direction DZ. The Z-direction DZ is orthogonal to the X-direction DX and orthogonal to the Y-direction DY. The base portion 37c is transparent. The base portion 37c may be made of the same material as the transmissive portion 37b. The base portion 37c may be seamless with the transparent portion 37b. The base portion 37c may be integrally molded with the transmission portion 37b. The width of each transmissive portion 37b in the X direction DX is wide at positions close to the base portion 37c and narrows away from the base portion 37c. The light control sheet 37 may be arranged such that the base portion 37 c faces the combiner 40 . The light control sheet 37 may be arranged such that the base portion 37 c faces the image forming apparatus 30 .

The light control sheet 37 regulates the traveling direction of transmitted light within a plane parallel to both the X-direction DX and the Z-direction DZ within a certain angular range. The light control sheet 37 does not restrict the traveling direction of transmitted light within a plane parallel to both the Y direction DY and the Z direction DZ. The light control sheet 37 has the function of strongly restricting the output angle in the X direction DX, but does not have the function of strongly restricting the output angle in the Y direction DY. The light control sheet 37 strongly controls the traveling direction in the X direction DX and does not strongly control the traveling direction in the Y direction DY. Therefore, the optical path adjustment member 34 including the light control sheet 37 has a strong diffusion function in the Y direction DY and a weak diffusion function in the X direction DX. The optical path adjustment member 34 including the light control sheet 37 may be incorporated into the head-up display 20 so that the Y direction DY crosses the first evaluation plane P1. The optical path adjustment member 34 including the light control sheet 37 may be incorporated into the head-up display 20 so that the Y direction DY is orthogonal to the first evaluation plane P1.

As shown in FIG. 16 , the optical path adjustment member 34 may include a light diffusion sheet 38 together with the light control sheet 37 . The light diffusion sheet 38 may have an isotropic diffusion function. The light diffusion sheet 38 may include a sheet-like transparent portion and a diffusion component dispersed within the transparent portion. Also, the base portion 37c of the light control sheet 37 may contain a diffusion component. Examples of diffusion components include metal compounds, gas-containing porous substances, resin beads around which metal compounds are retained, white fine particles, and simple air bubbles.

As shown in FIG. 17, the optical path adjustment member 34 may include an anisotropic light diffusion sheet 39. The anisotropic light diffusion sheet 39 is not particularly limited. The anisotropic light diffusion sheet 39 shown in FIG. 17 is subjected to hairline processing. The anisotropic light diffusion sheet 39 shown in FIG. 17 mainly diffuses in the X direction DX. The illustrated anisotropic light diffusion sheet 39 has a strong diffusion function in the X direction DX and a weak diffusion function in the Y direction DY. Therefore, the anisotropic light diffusion sheet 39 may be incorporated into the head-up display 20 so that the X direction DX crosses the first evaluation surface P1. The anisotropic light diffusion sheet 39 may be incorporated into the head-up display 20 such that the X direction DX is orthogonal to the first evaluation surface P1.

The anisotropic light diffusion sheet 39 is not limited to hairline processing. For example, the anisotropic light diffusion sheet 39 may include a base material and a diffusion component having a refractive index different from that of the base material. The anisotropic light diffusion sheet 39 can exhibit an anisotropic diffusion function by arranging the diffusion components in one direction having the longitudinal direction.

In addition, as a result of extensive studies by the inventors of the present invention, a second noise image of the external light source 90 as shown in FIG. 92 were observed. The reason for the appearance of the second noise image 92 is as follows. As shown in FIG. 12, the noise light L122 from the external light source 90 is incident on the combiner 140 via the second surface 142 unlike the image light L121 from the image forming apparatus 130 . This noise light L122 travels in the opposite direction parallel to the image light L121. The noise light L122 satisfies the Bragg condition of the hologram recording layer 162, like the image light L121. Noise light L122 is diffracted by hologram element 160 with high diffraction efficiency. The diffracted noise light L122 reaches the second surface 142 and is reflected by the second surface 142 . Reflection on the second surface 142 is regular reflection. After that, noise light L122 passes through hologram element 160 without being diffracted by hologram element 160 . Noise light L122 is emitted from combiner 140 toward user 5 . The noise light L122 forms a second noise image 92, and the user 5 observes the second noise image 92 of the external light source 90 behind the combiner 140. FIG. Like the noise image 91, the second noise image 92 can be observed at a position greatly deviated from the position of the external light source 90 that should be there. Therefore, the user 5 feels uncomfortable. The appearance of the second noise image 92 reduces the display quality of the head-up display 120 and reduces visibility through the combiner 140 .

In FIG. 10, the dotted line indicates the optical path along which the hologram recording layer 62 diffracts the image light L101 in the specular direction. Noise light L102A, which travels in the opposite direction along the incident optical path of image light L101 to combiner 40 and enters second surface 42 of combiner 40, is diffracted by hologram recording layer 62 in the specular direction. The noise light L102A is further specularly reflected by the second surface 42 . The direction of emission from the combiner 40 of the noise light L102A forming the second noise image 92 is parallel to the direction of incidence on the combiner 40 . The thickness of the combiner 40 is sufficiently thin, and the second noise image 92 is observed overlapping the external light source 90 .

That is, the hologram element 60 diffracts the image light L101 in the regular reflection direction with respect to the incident direction of the image light L101 to the combiner 40, thereby making the second noise image 92 inconspicuous. Therefore, it is possible to suppress discomfort caused by the second noise image 92, thereby improving the visibility. As confirmed by the inventors of the present invention, the hologram element 60 diffracts the image light L101 in a direction inclined at an angle of 25° or less in the specular direction with respect to the incident direction of the image light L101 to the combiner 40, resulting in the second noise The sense of discomfort caused by the image 92 can be sufficiently suppressed. As in the case of suppressing the discomfort due to the noise image 91, from the viewpoint of suppressing the discomfort due to the second noise image 92, the difference between the incident angle θ1 to the hologram element 60 and the diffraction angle θ2 at the hologram element 60 is determined. The height may be 20° or less, 15° or less, 10°, 5°, or 3°.

As described above, the diffraction angle θ2 may be different from the incident angle θ1 in terms of making it easier to distinguish the virtual image 80 from the ghost image 81 of the image light. In this case, the diffraction angle θ2 of the image light L101 may be larger than the incident angle θ1 of the image light L101. According to this setting, the traveling direction of the noise light L102 that has passed through the combiner 40 is greatly inclined from the traveling direction of the image light L101 that forms the virtual image 80 .

Here, in the example shown in FIG. 10, the image light L101 indicated by the solid line is diffracted by the hologram element 60 so that the diffraction angle θ2 is larger than the incident angle θ1. A solid line in FIG. 10 shows the optical path of the noise light L102 when the hologram element 60 having this diffraction characteristic is used.

The image light L101A indicated by the dotted line in FIG. 10 is diffracted by the hologram element 60 so that the diffraction angle θ2 becomes equal to the incident angle θ1. The optical path of the noise light L102 when the hologram element 60 having this diffraction characteristic is used is indicated by a dotted line in FIG.

The image light L101B indicated by the two-dot chain line in FIG. 10 is diffracted by the hologram element 60 so that the diffraction angle θ2 is smaller than the incident angle θ1. The optical path of the noise light L102B when the hologram element 60 having this diffraction characteristic is used is indicated by a chain double-dashed line in FIG.

As shown in FIG. 10, the optical path of the noise light forming the second noise image 92 is symmetrical with the optical path of the image light forming the virtual image 80 with respect to the normal direction ND. In the head-up display 20 applied to the front window 14 of the automobile 12, in a cross section including the image light L101 and the normal direction ND of the combiner 40, the incident light and the diffracted light of the image light L101 are normally normal It inclines to the opposite side with respect to the direction ND. Therefore, when the diffraction angle θ3 of the image light L101 becomes larger than the incident angle θ1 of the image light L101, the traveling direction of the noise light is greatly inclined with respect to the traveling direction of the image light. As a result, even if the hologram element 60 is enlarged to some extent, the noise light travels to a position different from the position to which the image light travels. That is, the noise light stops advancing toward the user 5 . As a result, even if the second noise image 92 of the external light source 90 is displayed, it is not observed by the user 5 . That is, the hologram element 60 diffracts the image light so that the diffraction angle θ2 is larger than the incident angle θ1, thereby effectively suppressing the discomfort caused by the second noise image 92 of the external light source 90 .

From the viewpoint of suppressing the discomfort caused by the second noise image 92 of the external light source 90, the diffraction angle θ2 may be increased. Since the image light L101 and the noise light L102 travel in symmetrical directions with respect to the normal direction ND, the second noise image 92 can also be made difficult for the user 5 to observe by increasing the diffracted light θ2. The magnitude of the diffraction angle θ2 can be appropriately set according to the application. A head-up display 20 applied to a front window 14 of an automobile 12
Then, the diffraction angle θ2 of the image light by the hologram element 60 of the combiner 40 may be 30° or more, 35° or more, 40° or more, or 45° or more. This setting makes it difficult for the noise light to travel toward the user 5 .

As described above, by adjusting the direction in which the image light is diffracted by the hologram element 60, it is possible to suppress the discomfort of the noise image 91. In the head-up display 20 applied to the front window 14 of the automobile 12, the discomfort of the noise image 91 can also be suppressed by adjusting the tilt angle θ5 of the combiner 40 and the incident angle θ1 of the image light L74. As shown in FIG. 7, the tilt angle θ5 (°) of the combiner 40 is the magnitude of the angle formed by the normal direction ND of the combiner 40 with respect to the vertical direction (the third direction D3 in the illustrated example). , is less than 90°. The tilt angle θ5 (°) of the combiner 40 is specified as the tilt angle at the central position (center of gravity position) of the region of the combiner 40 where the image light can enter. The incident angle θ1 (°) of the image light is specified as the incident angle of the image light incident on the central position of the region of the combiner 40 where the image light can be incident, as described above.

In the head-up display 20 applied to the front window 14 of the automobile 12, the image light L74 from the image forming device 30 normally enters the combiner 40 from below in the vertical direction. Then, in a cross section including the image light L74 and the normal direction ND of the combiner 40, the incident light and the diffracted light of the image light L74 are generally inclined opposite to the normal direction ND. At this time, by increasing the angle θ6 (°), which is the sum of the tilt angle θ5 (°) of the combiner 40 and the incident angle θ1 (°) of the image light to the combiner 40, the discomfort due to the noise image 91 can be suppressed. As the angle θ6 (°) increases, the noise light L71 forming the noise image 91 enters the combiner 40 from a direction greatly inclined with respect to the vertical direction. An external light source 90 such as an outdoor light or the sun is normally positioned vertically above the vehicle 12 . Therefore, by increasing the angle θ6 (°), it becomes difficult for the noise light L71 forming the noise image 91 to enter the combiner 40 . As a result, by increasing the angle θ6 (°), the noise image 91 can be made inconspicuous, and discomfort caused by the noise image 91 can be suppressed. From the viewpoint of suppressing discomfort caused by the noise image 91, the angle θ6 (°), which is the sum of the tilt angle θ5 (°) of the combiner 40 and the incident angle θ1 (°) of the image light to the combiner 40, may be 70° or more. , may be 80° or more, may be 90° or more, may be greater than 90°, or may be 100° or more.

In the head-up display 20 using the front window 14 of the automobile 12, the tilt angle θ5 of the combiner 40 and the incident angle θ1 of the image light to the combiner 40 may be set as follows. The inclination angle θ5 of the combiner 40 is set to 25° or more and 55° or less, and the magnitude of the incident angle θ1 of the image light to the combiner 40 is set to an angle larger than 0° and 60° or less than the magnitude of the inclination angle θ5 of the combiner 40. You can make it bigger. The tilt angle θ5 of the combiner 40 is set to 25° or more and 50° or less, and the magnitude of the incident angle θ1 of the image light to the combiner 40 is set to be 10° or more and 60° or less than the magnitude of the tilt angle θ5 of the combiner 40. You can make it bigger. The inclination angle θ5 of the combiner 40 is set to 25° or more and 45° or less, and the magnitude of the incident angle θ1 of the image light to the combiner 40 is increased by an angle larger than 20° and 60° or less than the magnitude of the inclination angle θ5 of the combiner 40. You can make it bigger. The tilt angle θ5 of the combiner 40 is set to 25° or more and 40° or less, and the magnitude of the incident angle θ1 of the image light to the combiner 40 is set to be more than 30° and 60° or less than the magnitude of the tilt angle θ5 of the combiner 40. You can make it bigger. According to the above settings, the size of the diffracted light θ2 is likely to be smaller than the size of the incident angle θ1, thereby facilitating observation of the virtual image 80 while distinguishing it from the ghost image 81 . Further, according to the above setting, the diffraction angle θ2 of the image light at the combiner 40 tends to be large, and the second noise image 92 can be made difficult to observe. Furthermore, according to the above settings, the angle θ6 (°), which is the sum of the tilt angle θ5 of the combiner 40 and the incident angle θ1 (°) of the image light to the combiner 40, tends to increase, and the noise image 91 is formed. The image can be made difficult to enter the combiner 40 .

In the above, the means for suppressing the discomfort due to the noise image 91, the means for suppressing the discomfort due to the second noise image 92, and the means for suppressing the decrease in visibility due to the ghost image 81 have been described. may be used.

D1: first direction, D2: second direction, D3: third direction, ND: normal direction, L4A: reference light, L4B: object light, L3A: illumination light, L3B: reproduced light, 5: user, 10 : moving body 12: automobile 14: front window 20: head-up display 25: projection device 25a: emission end 30: image forming device 31: image forming unit 32: light shielding member 34: optical path adjustment Member 35: Projection optical system 36: Lens sheet 36a: Body portion 36b: Unit lens 37: Light control sheet 37a: Absorption portion 37b: Transmission portion 37c: Base portion 38: Light diffusion sheet 39: anisotropic light diffusion sheet, 40: combiner, 41: first surface, 42: second surface, 45: bonding layer, 51: first substrate, 52: second substrate, 56: transparent plate, 57: antireflection layer , 57a: low refractive index layer, 57b: high refractive index layer, 60: hologram element, 62: hologram recording layer, 63: photosensitive material layer, 64: first sheet, 66: second sheet, 71: for reference light Lens 72: Object light lens 80: Virtual image 81: Ghost image 90: External light source 91: Noise image 95: Optical axis

Claims

A combiner for a head-up display that projects image light,
a first substrate including a first surface serving as an incident surface of the image light;
a second substrate including a second surface facing the first surface;
a bonding layer that bonds the first substrate and the second substrate;
a hologram element positioned between the first substrate and the second substrate;
the hologram element diffracts the image light in a direction of specular reflection with respect to the direction of incidence of the image light on the combiner or in a direction inclined at an angle of 25° or less to the direction of specular reflection;
The distance between the display position of the image by the image light diffracted by the hologram element and the hologram element is the distance between the display position of the image by the image light reflected by the first surface or the second surface and the hologram element. A combiner for a head-up display that is 4x or more.
A combiner for a head-up display that projects image light,
a first substrate including a first surface serving as an incident surface of the image light;
a second substrate including a second surface facing the first surface;
a bonding layer that bonds the first substrate and the second substrate;
a hologram element positioned between the first substrate and the second substrate;
An image of an external light source reproduced by light emitted from an external light source, incident on the combiner from the second surface, reflected by the first surface and then diffracted by the hologram element is observed through the combiner. A combiner for a head-up display that is viewed at least partially overlapping a real image of an external light source.
The distance between the display position of the image by the image light diffracted by the hologram element and the hologram element is the distance between the display position of the image by the image light reflected by the first surface or the second surface and the hologram element. 3. The combiner for head-up display according to claim 2, which is 4 times or more.
The combiner for a head-up display according to any one of claims 1 to 3, wherein said first substrate includes an antireflection layer forming said first surface.
A combiner for a head-up display that projects image light,
a first substrate including a first surface serving as an incident surface of the image light;
a second substrate including a second surface facing the first surface;
a bonding layer that bonds the first substrate and the second substrate;
a hologram element positioned between the first substrate and the second substrate;
the hologram element diffracts the image light in a direction of specular reflection with respect to the direction of incidence of the image light on the combiner or in a direction inclined at an angle of 25° or less to the direction of specular reflection;
A combiner for a head-up display, wherein the first substrate includes an antireflection layer forming the first surface.
a projection device that emits image light;
and the combiner according to claim 1, 2 or 5 for projecting the image light.
7. The head-up display according to claim 6, wherein a difference between an incident angle of said image light to said combiner and a diffraction angle of said image light at said combiner is 3° or more.
7. The head-up display according to claim 6, wherein the diffraction angle of said image light at said combiner is greater than the angle of incidence of said image light on said combiner.
a light shielding member arranged to be shifted from the optical path of the image light emitted from the projection device and diffracted by the hologram element of the combiner;
7. The head-up display according to claim 6, wherein said light shielding member shields part of image light emitted from said projection device and directed toward said combiner.
The projection device includes an image forming device that emits the image light, and an optical path adjusting member that is arranged between the image forming device and the combiner and adjusts an optical path of the image light,
7. The head-up display according to claim 6, wherein said optical path adjustment member has an anisotropic diffusion function.
The optical path adjusting member is perpendicular to the first evaluation surface and the optical axis rather than the first evaluation surface parallel to both the normal direction of the combiner and the optical axis of the image light incident on the combiner. 11. The head-up display according to claim 10, having a strong diffusion function in the parallel second evaluation plane.
A moving body comprising the head-up display according to claim 6.
A head-up display according to claim 6,
The automobile, wherein the optical path length of the image light from the projection device to the combiner is 200 mm or more.
A head-up display according to claim 6,
The formula "Lz × sin θ4" using the optical path length Lz (mm) and the angle θ4 (°) is 10 mm or more,
The optical path length Lz (mm) is the optical path length of the image light from the projection device to the combiner,
The motor vehicle, wherein the angle θ4 is the difference between the magnitude of the incident angle of the image light to the combiner and the magnitude of the diffraction angle of the image light at the combiner.
A head-up display according to claim 6,
The motor vehicle, wherein the diffraction angle of the image light at the combiner is 30° or more.
A head-up display according to claim 6,
The sum of the tilt angle of the combiner and the incident angle of the image light to the combiner is 70° or more,
The motor vehicle, wherein the tilt angle of the combiner is the angle between the normal direction and the vertical direction of the combiner.
A head-up display according to claim 6,
A motor vehicle, wherein a magnitude of an angle of diffraction of said image light at said combiner is smaller than a magnitude of an angle of incidence of said image light on said combiner.
A head-up display according to claim 6,
A motor vehicle, wherein part of the image light is reflected by the first surface or the second surface in a direction inclined upward with respect to a horizontal direction.
the magnitude of the incident angle of the image light to the combiner is greater than the magnitude of the tilt angle of the combiner;
18. Vehicle according to claim 17, wherein the tilt angle of the combiner is the angle between the normal direction of the combiner and the vertical direction.
A head-up display according to claim 6,
The tilt angle of the combiner is 25° or more and 55° or less,
the magnitude of the incident angle of the image light to the combiner is greater than the magnitude of the tilt angle of the combiner by an angle greater than 0° and less than or equal to 60°;
The motor vehicle, wherein the tilt angle of the combiner is the angle between the normal direction and the vertical direction of the combiner.
A head-up display comprising a projection device that emits image light and a combiner that projects the image light,
The combiner is
a first substrate including a first surface serving as an incident surface of the image light;
a second substrate including a second surface facing the first surface;
a bonding layer that bonds the first substrate and the second substrate;
a hologram element positioned between the first substrate and the second substrate;
The head-up display, wherein a diffraction angle of the image light at the combiner is larger than an incident angle of the image light to the combiner.
A vehicle equipped with a head-up display,
The head-up display includes a projection device that emits image light and a combiner that projects the image light,
The combiner is
a first substrate including a first surface serving as an incident surface of the image light;
a second substrate including a second surface facing the first surface;
a bonding layer that bonds the first substrate and the second substrate;
a hologram element positioned between the first substrate and the second substrate;
The automobile, wherein the optical path length of the image light from the projection device to the combiner is 200 mm or more.
A vehicle equipped with a head-up display,
The head-up display includes a projection device that emits image light and a combiner that projects the image light,
The combiner is
a first substrate including a first surface serving as an incident surface of the image light;
a second substrate including a second surface facing the first surface;
a bonding layer that bonds the first substrate and the second substrate;
a hologram element positioned between the first substrate and the second substrate;
The formula "Lz × sin θ4" using the optical path length Lz (mm) and the angle θ4 (°) is 10 mm or more,
The optical path length Lz (mm) is the optical path length of the image light from the projection device to the combiner,
The motor vehicle, wherein the angle θ4 (°) is a difference between an incident angle of the image light to the combiner and a diffraction angle of the image light at the combiner.
A vehicle equipped with a head-up display,
The head-up display includes a projection device that emits image light and a combiner that projects the image light,
The combiner is
a first substrate including a first surface serving as an incident surface of the image light;
a second substrate including a second surface facing the first surface;
a bonding layer that bonds the first substrate and the second substrate;
a hologram element positioned between the first substrate and the second substrate;
The motor vehicle, wherein the diffraction angle of the image light at the combiner is 30° or more.
A vehicle equipped with a head-up display,
The head-up display includes a projection device that emits image light and a combiner that projects the image light,
The combiner is
a first substrate including a first surface serving as an incident surface of the image light;
a second substrate including a second surface facing the first surface;
a bonding layer that bonds the first substrate and the second substrate;
a hologram element positioned between the first substrate and the second substrate;
The sum of the inclination angle of the combiner and the incident angle of the image light to the combiner is 70° or more,
The motor vehicle, wherein the tilt angle of the combiner is the angle between the normal direction and the vertical direction of the combiner.
A vehicle equipped with a head-up display,
The head-up display includes a projection device that emits image light and a combiner that projects the image light,
The combiner is
a first substrate including a first surface serving as an incident surface of the image light;
a second substrate including a second surface facing the first surface;
a bonding layer that bonds the first substrate and the second substrate;
a hologram element positioned between the first substrate and the second substrate;
A motor vehicle, wherein a magnitude of an angle of diffraction of said image light at said combiner is smaller than a magnitude of an angle of incidence of said image light on said combiner.
A vehicle equipped with a head-up display,
The head-up display includes a projection device that emits image light and a combiner that projects the image light,
The combiner is
a first substrate including a first surface serving as an incident surface of the image light;
a second substrate including a second surface facing the first surface;
a bonding layer that bonds the first substrate and the second substrate;
a hologram element positioned between the first substrate and the second substrate;
A motor vehicle, wherein part of the image light is reflected by the first surface or the second surface in a direction inclined upward with respect to a horizontal direction.
A vehicle equipped with a head-up display,
The head-up display includes a projection device that emits image light and a combiner that projects the image light,
The combiner is
a first substrate including a first surface serving as an incident surface of the image light;
a second substrate including a second surface facing the first surface;
a bonding layer that bonds the first substrate and the second substrate;
a hologram element positioned between the first substrate and the second substrate;
The tilt angle of the combiner is 25° or more and 55° or less,
the magnitude of the incident angle of the image light to the combiner is greater than the magnitude of the tilt angle of the combiner by an angle greater than 0° and less than or equal to 60°;
The motor vehicle, wherein the tilt angle of the combiner is the angle between the normal direction and the vertical direction of the combiner.
an image forming device that emits image light;
a combiner projected with the image light;
an optical path adjustment member disposed between the image forming apparatus and the combiner and adjusting an optical path of the image light;
The combiner is
a first substrate including a first surface serving as an incident surface of the image light;
a second substrate including a second surface facing the first surface;
a bonding layer that bonds the first substrate and the second substrate;
a hologram element positioned between the first substrate and the second substrate;
The magnitude of the diffraction angle of the image light at the combiner is different from the magnitude of the incident angle of the image light to the combiner,
the hologram element diffracts the image light in a direction inclined with respect to a specular reflection direction with respect to an incident direction of the image light to the combiner;
The optical path adjustment member is perpendicular to the first evaluation surface and the optical path of the combiner rather than in the first evaluation surface parallel to both the normal direction of the combiner and the optical axis of the image light incident on the combiner. A head-up display having a strong diffusion function in a second evaluation plane parallel to the normal direction.