Display device

Abstract

A display device of the present invention comprises: an image light emission unit (50) that outputs image light; and a light guide plate (30) that includes a hologram element (40), on which the image light emitted by the image light emission unit (50) is incident, and a light guide unit containing the hologram element (40). The hologram element (40) is provided with an incident hologram element (41) on which the image light is incident. The image light emission unit (50) varies the widths (W11, W12, W13) of the image light incident on the incident hologram element (41), on the basis of the viewing angle of the image light.

Description

Display device

[0001] The present disclosure relates to a display device.

[0002] As a conventional technology, a light guide plate for a head-up display that includes a plurality of hologram elements in the light guide plate is known. For example, Patent Document 1 discloses an optical device including a first light guide plate, a second light guide plate, a first deflection unit provided on the first light guide plate and having a volume hologram diffraction grating, and a second deflection unit provided on the second light guide plate and having a volume hologram diffraction grating, wherein the first deflection unit and the second deflection unit emit diffracted light.

[0003] Japanese Unexamined Patent Publication No. 2020-112746

[0004] In the optical device of the conventional art, when light diffracted by the volume hologram diffraction grating propagates, the propagation angle varies depending on the viewing angle, and the shift distance of the emitted light may differ during one round trip in the thickness direction of the light guide plate. In this case, part of the light emitted from the light guide plate may overlap, while other parts of the light do not overlap. Therefore, when the light emitted from the optical device is projected onto a display medium, bright streaks or dark streaks occur, which degrades the image quality.

[0005] Therefore, the present disclosure can improve the quality of an image projected onto a display medium.

[0006] A display device according to an aspect of the present disclosure includes: an image light emitting unit that outputs image light; and a light guide plate having a hologram element into which the image light emitted from the image light emitting unit enters, and a light guide section enclosing the hologram element. The hologram element includes an incident hologram element on which the image light is incident, and the image light emitting unit varies the width of the image light incident on the incident hologram element based on the angle of view of the image light.

[0007] According to the display device of the present disclosure, the quality of an image projected onto a display medium can be improved.

[0008] Figure 1A is a schematic diagram showing an example of a vehicle on which the display device according to the embodiment is installed. Figure 1B is a schematic diagram showing the display device and vehicle according to the embodiment viewed from the side. Figure 2 is a perspective view showing the display device according to the embodiment. Figure 3 is a diagram showing the display device according to the embodiment. Figure 4A is a diagram showing the first image light emitted from the first hologram element when image light of different angles of view is incident on the first hologram element according to the embodiment. Figure 4B is an explanatory diagram showing the intensity distribution of image light of each angle of view incident on the incident surface according to the embodiment. Figure 4C is a diagram showing the second image light emitted from the second hologram element when image light of different angles of view is incident on the first hologram element according to the embodiment. Figure 5A is a diagram showing the second image light emitted from the second hologram element when first image light of different angles of view is incident on the second hologram element according to the embodiment. Figure 5B is a diagram showing the third image light emitted from the third hologram element when first image light of different angles of view is incident on the second hologram element according to the embodiment. Figure 6 is an explanatory diagram showing each image light propagating within the light guide plate when the width of the image light at each field of view is the same, which is a comparative example. Figure 7 is an explanatory diagram showing the internal configuration of the image light emission unit according to the embodiment. Figure 8 is a perspective view showing the second optical body according to the embodiment. Figure 9 is an explanatory diagram showing each image light propagating within the light guide plate when the width of the image light at each field of view is different in the image light emission unit according to the embodiment. Figure 10 is an explanatory diagram showing the relationship between the aperture size of the second lens and the transmitted light according to the embodiment. Figure 11 is a cross-sectional view showing an example of the second optical body according to the embodiment.

[0009] The embodiments will be described in detail below with reference to the drawings.

[0010] The embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, arrangement and connection configurations of components, steps, and the order of steps shown in the following embodiments are examples only and are not intended to limit this disclosure. Furthermore, any components in the following embodiments that are not described in an independent claim will be described as optional components.

[0011] Furthermore, each figure is a schematic diagram and not necessarily a strictly accurate representation. Also, the same component is denoted by the same reference numeral in each figure.

[0012] Furthermore, in the following embodiments, expressions such as rectangular, substantially parallel, and in the X-axis direction are used. For example, rectangular, substantially parallel, and in the X-axis direction not only means that it is perfectly rectangular, parallel, and in the X-axis direction, but also substantially rectangular, parallel, and in the X-axis direction, that is, including an error of a few percent. Also, rectangular, parallel, and in the X-axis direction means rectangular, substantially parallel, and in the X-axis direction to the extent that the effects of this disclosure can be achieved. The same applies to other expressions using "shape," "subjectively," and "direction."

[0013] In Figure 1B, the alignment direction of the second hologram element relative to the first hologram element is defined as the positive X-axis direction, the alignment direction of the second hologram element relative to the third hologram element is defined as the positive Y-axis direction, and the alignment direction of the first hologram element relative to the image generation device is defined as the positive Z-axis direction. The correspondence in Figure 1B may be applied to each figure.

[0014] (Embodiment) <Configuration> First, the configuration of the display device 1 will be explained using Figures 1A to 3.

[0015] Figure 1A is a schematic diagram showing an example of a vehicle 2 on which the display device 1 according to the embodiment is installed. Figure 1B is a schematic diagram showing the display device 1 and vehicle 2 according to the embodiment viewed from the side. Figure 2 is a perspective view showing the display device 1 according to the embodiment. Figure 3 is a diagram showing the display device 1 according to the embodiment. Figure 3(a) is a front view of the display device 1, Figure 3(b) is a side view of the display device 1, and Figure 3(c) is a front view of the display device 1.

[0016] As shown in Figures 1A and 1B, the display device 1 can cause image light to enter a person's eye by emitting and reflecting image light from a light reflector. For example, when the display device 1 is used in a vehicle 2, the display device 1 can cause image light to enter a person's eye by reflecting image light emitted from a display medium such as a front windshield 3, which is a light-transmitting member. In this case, by emitting image light, the display device 1 projects the image shown by the image light onto the light-transmitting member, and displays a virtual image corresponding to the image in front of the light-transmitting member. Image light is light that shows an image and displays a virtual image in front of the front windshield 3. The image can be a still image or a moving image, and is an image that shows numbers, letters, figures, etc.

[0017] As shown in Figures 1B and 2, the display device 1 comprises an image light emission unit 50 and a light guide plate 30.

[0018] The image light emission unit 50 is an image generation device that emits image light onto the light guide plate 30. The image light emission unit 50 emits image light representing a rectangular image, which is then projected onto the front windshield 3 via the light guide plate 30. This allows the user to perceive a virtual image. Details of the image light emission unit 50 will be described later.

[0019] The light guide plate 30 is a hologram light guide plate that displays the image indicated by the image light to the user. The light guide plate 30 is light-transmitting and can extend the image indicated by the image light emitted by the image light emission unit 50 in the X-axis and Y-axis directions before emission. The light guide plate 30 is arranged such that one side (emission surface 31b) faces the front windshield 3 and the other side (incident surface 31a) faces the image light emission unit 50.

[0020] The light guide plate 30 has an incident surface 31a and an exit surface 31b.

[0021] The incident surface 31a is positioned to face the output surface of the image light output unit 50. Image light emitted from the output surface of the image light output unit 50 is incident on the incident surface 31a. The incident surface 31a is part of the back surface of the light guide plate 30. The back surface is the surface of the light guide plate 30 opposite to the output surface 31b.

[0022] The emission surface 31b is the image light incident from the incident surface 31a, which propagates through the inside of the light guide plate 30 and is emitted toward the front windshield 3. The emission surface 31b faces the front windshield 3 and is positioned at a predetermined distance from the front windshield 3. The emission surface 31b is a part of the surface of the light guide plate 30.

[0023] As shown in Figures 2 and 3, the light guide plate 30 has a light-transmitting light guide portion 31 and a plurality of hologram elements 40.

[0024] The light guide section 31 has an incident surface 31a that faces the image light emission section 50. The incident surface 31a is a part of the back surface of the light guide section 31. The light guide section 31 also has an emission surface 31b that faces the front windshield 3. The emission surface 31b is a part of the front surface of the light guide section 31.

[0025] The light guide section 31 is made of a light-transmitting material such as glass and resin.

[0026] The light guide section 31 contains a plurality of holographic elements 40. As shown in Figure 3, the plurality of holographic elements 40 are light-transmitting optical elements that diffract and emit light propagating through the light guide section 31. The plurality of holographic elements 40 are contained within the light guide section 31 so as to be positioned substantially parallel to the incident surface 31a and the outgoing surface 31b of the light guide section 31.

[0027] Such a plurality of hologram elements 40 are made of a light-transmitting material. The plurality of hologram elements 40 includes a first hologram element 41, a second hologram element 42, and a third hologram element 43. In this embodiment, three hologram elements are given as an example of the plurality of hologram elements 40, but the embodiment is not limited to this. For example, the plurality of hologram elements 40 may be two. Specifically, the plurality of hologram elements may include an incident hologram element into which image light is incident and an exit hologram element into which image light is incident.

[0028] The first hologram element 41 and the second hologram element 42 are arranged side by side along the X-axis. The second hologram element 42 and the third hologram element 43 are arranged side by side along the Y-axis. Furthermore, the first hologram element 41 is positioned so that, when viewed along the Z-axis, it overlaps with the incident surface 31a of the light guide plate 30 and also overlaps with the emission surface of the image light emission unit 50 located on the Z-minus side of the light guide plate 30.

[0029] The first hologram element 41 is an incident hologram element to which the image light emitted from the image light emission unit 50 is incident.

[0030] Image light traveling along the positive Z-axis direction, emitted from the emission surface of the image light emission unit 50, is incident on the first hologram element 41. The first hologram element 41 emits the incident image light toward the second hologram element 42. Specifically, the first hologram element 41 emits first image light (bent light), which is the image light from the image light emission unit 50 that was incident from the incidence surface 31a, toward the second hologram element 42. More specifically, as the image light incident on the light guide plate 30 propagates within the light guide plate 30, the first hologram element 41 deflects the image light by diffraction according to the diffraction efficiency of the first hologram element 41, and emits it as first image light propagating along the positive X-axis direction. The first image light deflected by diffraction in the first hologram element 41 is incident on the second hologram element 42.

[0031] The second hologram element 42 is located on the positive X-axis side of the first hologram element 41, on the light emission side of the first hologram element 41, and on the positive Y-axis side of the third hologram element 43, on the light incidence side of the third hologram element 43.

[0032] The second hologram element 42 is elongated along the X-axis and is a folded hologram element that diffracts the first image light emitted from the first hologram element 41 and emits the second image light to the third hologram element 43.

[0033] The first image light emitted from the first hologram element 41 is incident on the second hologram element 42. The second hologram element 42 further deflects the first image light, which has been deflected by diffraction by the first hologram element 41, by further diffraction, and emits a deflected second image light (deflected light). Specifically, in the second hologram element 42, the first image light that has passed through the first hologram element 41 is incident (transmitted) while repeatedly reflecting off the light guide plate. Each time the first image light is incident on the second hologram element 42, the second hologram element 42 emits a second image light, which has been further deflected by diffraction, toward the third hologram element 43. More specifically, as the first image light incident on the second hologram element 42 propagates through the light guide plate 30 along the positive X-axis direction, the second hologram element 42 further deflects the first image light by diffraction according to the diffraction efficiency of the second hologram element 42. At this time, the second hologram element 42 stretches the image of the first image light along the X-axis direction. As a result, the second hologram element 42 emits the second image light, which has been stretched along the X-axis, along the negative Y-axis direction. The second image light, deflected by diffraction in the second hologram element 42, is incident on the third hologram element 43.

[0034] The third hologram element 43 is located on the negative Y-axis side of the second hologram element 42 and is positioned on the light-emitting side of the second hologram element 42. Furthermore, the third hologram element 43 is positioned so as to overlap with and face the light-emitting surface 31b of the light guide plate 30.

[0035] The third hologram element 43 is an emission hologram element that has a rectangular shape when viewed along the Z-axis.

[0036] The second image light emitted from the second hologram element 42 is incident on the third hologram element 43. The third hologram element 43 further deflects the second image light, which has been deflected by diffraction by the second hologram element 42, by diffraction, and emits the deflected third image light (deflected light) to the outside of the light guide plate 30. Specifically, the second image light that has passed through the second hologram element 42 is incident on (transmitted) to the third hologram element 43. Each time the second image light is incident on the third hologram element 43, the third hologram element 43 emits third image light, which has been further deflected by diffraction by the incident second image light, at a predetermined emission angle. More specifically, as the second image light, which has been deflected by diffraction by the second hologram element 42, propagates through the light guide plate 30 along the negative Y-axis direction, the third hologram element 43 further deflects the second image light by diffraction according to the diffraction efficiency of the third hologram element 43. At this time, the third hologram element 43 further stretches the image of the second image light, which has been stretched along the X-axis, along approximately the Y-axis. As a result, the third hologram element 43 emits the third image light, which has been stretched along the X-axis and approximately the Y-axis, to the outside of the light guide plate 30 at a predetermined emission angle. In other words, the third hologram element 43 emits the third image light, which has been expanded in the X-axis and Y-axis directions, at a predetermined emission angle by further stretching the second image light emitted by the second hologram element 42 along approximately the Y-axis. In this embodiment, the third hologram element 43 emits the third image light in the Z-axis positive direction so that it is directed toward the front windshield 3.

[0037] Here, the predetermined emission angle is the emission angle of the third image light emitted from the third hologram element 43, and is the angle of the light emitted with respect to the normal of the emission surface of the third hologram element 43.

[0038] Next, using Figures 4A to 5B, we will explain the intensity distribution of image light emitted from the light guide plate 30 according to the field of view.

[0039] Figure 4A shows the first image light emitted from the first hologram element 41 when image light with a different field of view is incident on the first hologram element 41 according to the embodiment. Figure 4B is an explanatory diagram showing the intensity distribution of image light with each field of view incident on the incident surface 31a according to the embodiment. Figure 4C shows the second image light emitted from the second hologram element 42 when image light with a different field of view is incident on the first hologram element 41 according to the embodiment. Figure 5A shows the second image light emitted from the second hologram element 42 when first image light with a different field of view is incident on the second hologram element 42 according to the embodiment. Figure 5B shows the third image light emitted from the third hologram element 43 when first image light with a different field of view is incident on the second hologram element 42 according to the embodiment. Furthermore, Figure 4B(a) shows the case when image light with a field of view of g1 is incident on the incident surface 31a, Figure 4B(b) shows the case when image light with a field of view of g2 is incident on the incident surface 31a, and Figure 4B(c) shows the case when image light with a field of view of g3 is incident on the incident surface 31a. The same applies to Figures 4C and 5B.

[0040] As shown in Figure 4A, the image light emitted from the image light emission unit 50 is incident on the incident surface 31a of the light guide plate 30, but the angle of the image light incident on the incident surface 31a differs depending on the field of view. For example, image light with field of view g1, image light with field of view g2, and image light with field of view g3 are incident on the incident surface 31a.

[0041] The first hologram element 41, the second hologram element 42, and the third hologram element 43 have uniform diffraction efficiency. Therefore, as shown in Figure 4B, the intensity distribution of the first hologram element 41, the intensity distribution of the second hologram element 42 in the second direction, and the intensity distribution of the third hologram element 43 in both the first and second directions are all rectangular in shape.

[0042] In this case, as shown in (a) of FIG. 5B, when the image light that has entered the first hologram element 41 at an angle of view g1 is emitted as third image light from the third hologram element 43, the intensity distribution shifts, and a gap is formed between the intensity distributions of two adjacent third image light beams. For this reason, when the third image light is projected onto the front window 3, dark streaks are visible in the image.

[0043] Further, as shown in (b) of FIG. 5B, when the image light that has entered the first hologram element 41 at an angle of view g2 is emitted as third image light from the third hologram element 43, no gap is formed between the intensity distributions of two adjacent third image light beams. For this reason, when the third image light is projected onto the front window 3, the image is visible appropriately.

[0044] Further, as shown in (c) of FIG. 5B, when the image light that has entered the first hologram element 41 at an angle of view g3 is emitted as third image light from the third hologram element 43, the intensity distribution shifts, and parts of the intensity distributions of two adjacent third image light beams overlap. For this reason, the third image light beams strengthen each other as indicated by the broken line, and when the third image light is projected onto the front window 3, bright streaks are visible in the image.

[0045] This can occur when image light beams with different angles of view g1, g2, and g3 have respectively equal widths when entering the first hologram element 41. FIG. 6 is an explanatory diagram showing each image light propagating through the light guide plate 30 in a comparative example where the widths of the image light beams at angles of view g1, g2, and g3 are equal. In FIG. 6, light at one end side in the width direction of each image light is indicated by a solid line, and light at the other end side is indicated by a broken line. The image light at the angle of view g1 is illustrated with the thickest line, the image light at the angle of view g3 is illustrated with the thinnest line, and the image light at the angle of view g2 is illustrated with a line of intermediate thickness. The image light emitting section 50 emits the image light beams at angles of view g1, g2, and g3 with equal widths W1, W2, and W3.

[0046] In this case, the image light with an angle of view g2 propagates through the light guide plate 30 along substantially the same path for the solid line and the broken line. In contrast, for the image light with an angle of view g1, a gap is formed when the solid line and the broken line are reflected, which is one of the causes of dark streaks in the image. Furthermore, for the image light with an angle of view g3, the solid line and the broken line overlap when reflected, which is one of the causes of bright streaks in the image. To suppress this, the image light emitting unit 50 varies the width of the image light incident on the first hologram element 41 based on the angle of view of the image light.

[0047] The details of the image light emitting unit 50 will be described. FIG. 7 is an explanatory diagram showing the internal structure of the image light emitting unit 50 according to the embodiment. As shown in FIG. 7, the image light emitting unit 50 includes a plurality of light sources 51, a plurality of reflectors 53, a plurality of lenses 52, a first optical body 54, a collimating lens 55, a second optical body 56, an image display element 59, and a polarizing beam splitter 58.

[0048] Each of the plurality of light sources 51 is a laser light source that emits light beams in different predetermined wavelength bands. In this embodiment, as an example of the plurality of light sources 51, a first light source 51a, a second light source 51b, and a third light source 51c are provided. For example, the first light source 51a can emit blue light. The second light source 51b can emit green light. The third light source 51c can emit red light.

[0049] The first light source 51a emits light toward the first optical body 54. The second light source 51b emits light in a direction different from that toward the first optical body 54. The third light source 51c emits light in a direction different from that toward the first optical body 54. That is, the direction of light emitted by the first light source 51a is different from the direction of light emitted by the second light source 51b and the third light source 51c. In this embodiment, the directions of light emitted by the second light source 51b and the third light source 51c are the same.

[0050] The light emitted from each of the multiple light sources 51 is focused by multiple lenses 52, which correspond one-to-one with each of the multiple light sources 51. In other words, the multiple lenses 52 are arranged in the direction of emission of the light emitted from each of the multiple light sources 51, so as to correspond one-to-one with each of the multiple light sources 51. The light focused by each of the multiple lenses 52 is incident on each of the multiple reflectors 53.

[0051] Each of the multiple reflectors 53 is positioned on the light rays emitted by the multiple light sources 51, and can reflect light rays of a predetermined wavelength band and transmit light rays of other wavelength bands. The reflectors 53 are, for example, dichroic mirrors with wavelength selectivity. Each of the multiple reflectors 53 may have different wavelength selectivity.

[0052] In this embodiment, as an example of multiple reflectors 53, a first reflector 53a, a second reflector 53b, and a third reflector 53c are provided. In this embodiment, the third reflector 53c, the second reflector 53b, the first reflector 53a, and the first light source 51a are arranged in that order from the first optical body 54 side.

[0053] The second reflector 53b is positioned opposite the third light source 51c. The second reflector 53b has the property of reflecting red light (light with a red wavelength component) and transmitting light other than red light. Therefore, the second reflector 53b reflects the red light emitted by the third light source 51c toward the first optical body 54.

[0054] The first reflector 53a is positioned to face the second light source 51b and the first light source 51a. Specifically, the first reflector 53a is positioned such that one side of the first reflector 53a faces the second light source 51b, and the other side of the first reflector 53a faces the first light source 51a.

[0055] The first reflector 53a has the property of reflecting green light (light with a green wavelength component). Therefore, the first reflector 53a reflects the green light emitted by the second light source 51b toward the second reflector 53b, that is, toward the first optical body 54.

[0056] Furthermore, the first reflector 53a also has the property of transmitting light other than green light. Therefore, the first reflector 53a transmits the blue light emitted by the first light source 51a and emits it towards the second reflector 53b.

[0057] The first optical element 54 is positioned between the third reflector 53c and the collimating lens 55. Light transmitted through the third reflector 53c is incident on the first optical element 54. The first optical element 54 is capable of shaping the contour of the incident light before emitting it. The contour of light refers to the shape of the light when it is shone onto a virtual plane. In this embodiment, the first optical element 54 can shape the contour of the light transmitted through the third reflector 53c and emit light with a rectangular contour towards the collimating lens 55.

[0058] The first optical element 54 is, for example, a microlens array or a lenticular lens. The first optical element 54 has a plurality of microlenses capable of shaping the outline of light emitted by the light source 51.

[0059] The collimating lens 55 is positioned between the first optical body 54 and the second optical body 56. Light emitted from the first optical body 54 enters the collimating lens 55, collimates the incident light, and directs it toward the second optical body 56.

[0060] The second optical element 56 is positioned between the collimating lens 55 and the polarizing beam splitter 58. The second optical element 56 is capable of shaping and emitting the outline of light from the collimating lens 55.

[0061] Figure 8 is a perspective view showing a second optical body 56 according to an embodiment. As shown in Figure 8, the second optical body 56 is a microlens array. The second optical body 56 is positioned optically conjugate to the first hologram element 41. The second optical body 56 has a plurality of second lenses 56a that can further refine the outline of the light emitted from the first optical body 54.

[0062] The second optical body 56 has a second incident surface 56a1 and a second exit surface 56a2 which is the surface opposite to the second incident surface 56a1. A plurality of second lenses 56a are formed on at least one of the second incident surface 56a1 and the second exit surface 56a2. In this embodiment, a plurality of second lenses 56a are formed on the second exit surface 56a2. The second lenses 56a are an example of microlenses. The plurality of second lenses 56a are arranged in an array (matrix).

[0063] As shown in Figure 7, the second incident surface 56a1 faces the collimating lens 55. Therefore, light emitted from the collimating lens 55 is incident on the second incident surface 56a1. The second exit surface 56a2 faces the polarizing beam splitter 58. Therefore, the second exit surface 56a2 emits light incident from the second incident surface 56a1 towards the polarizing beam splitter 58 via the field lens 57a. The field lens 57a focuses the light emitted by the second optical body 56 and emits it towards the polarizing beam splitter 58.

[0064] Light whose outline has been refined by the second optical body 56 is incident on the polarizing beam splitter 58. The polarizing beam splitter 58 reflects the light emitted by the second optical body 56 toward the image display element 59 and causes it to be incident on the image display element 59. Specifically, the image display element 59 is a liquid crystal display element such as LCOS (Liquid Crystal On Silicon), and is irradiated with light of multiple wavelength bands from the polarizing beam splitter 58. The image display element 59 then emits the irradiated light as image light toward the first hologram element 41a via the polarizing beam splitter 58 and projection lens 57b.

[0065] The projection lens 57b focuses the image light emitted by the image display element 59, which has passed through the polarizing beam splitter 58, and directs it to the incident surface of the light guide plate 30. The image light incident on the incident surface of the light guide plate 30 is then incident on the first hologram element 41, which becomes the pupil.

[0066] Here, as described above, the image light emitting unit 50 varies the width of the image light incident on the first hologram element 41 based on the field of view of the image light. Specifically, the image light emitting unit 50 varies the width of the image light based on the field of view using a plurality of second lenses 56a provided in the second optical body 56.

[0067] Figure 9 is an explanatory diagram showing the image light propagating within the light guide plate 30 when the image light emission unit 50 according to the embodiment has different widths for each of the field angles g1, g2, and g3. In Figure 9, the light at one end in the width direction of each image light is shown with a solid line, and the light at the other end is shown with a dashed line. The image light at field angle g1 is shown with the thickest line, the image light at field angle g3 is shown with the thinnest line, and the image light at field angle g2 is shown with a line of medium thickness. The image light emission unit 50 emits image light with different widths W11, W12, and W13 for each of the field angles g1, g2, and g3. Specifically, the width W11 of the image light at the largest field angle g1 is the largest, and the width W13 of the image light at the smallest field angle g3 is the smallest. In other words, as the field angle increases, the width of the image light also increases.

[0068] In this case, the image light for each field of view g1, g2, and g3 propagates through the light guide plate 30 along roughly the same path as the solid and dashed lines. Therefore, unlike the comparative example shown in Figure 6, dark and bright streaks are suppressed, and the quality of the image projected onto the front windshield 3 is improved.

[0069] In order for the image light emission unit 50 to produce different widths of image light for each field of view g1, g2, and g3, the following parameters are determined. The reflection period of the image light propagating within the light guide plate 30 is uniquely determined by the propagation angle of the light after diffraction by the first hologram element 41, the thickness of the light guide plate 30, the refractive index of the light guide plate 30, and the widths W11, W12, and W13 of the image light for each field of view g1, g2, and g3 incident from the image light emission unit 50 to the first hologram element 41. In other words, the widths W11, W12, and W13 of the image light for each field of view g1, g2, and g3 are determined by the reflection period, the propagation angle, and the thickness and refractive index of the light guide plate 30.

[0070] More specifically, in the case of a transmission diffraction grating such as a light guide plate 30 equipped with a first holographic element 41, Bragg's condition is expressed by the following equation (1).

[0071] d(sinθm−sinθi)=mλ...(1)

[0072] d is the lattice constant (lattice spacing), θi is the incident angle, θm is the diffraction angle (emission angle) of the mth-order light, m ​​is the diffraction order, and λ is the wavelength of light. In this embodiment, θm is approximately the diffraction angle of the first-order light. Based on this equation (1), by making the reflection period of the image light propagating within the light guide plate 30 equivalent to the width of the image light incident from the image light emission unit 50 to the first hologram element 41, as shown in Figure 9, the images for each field of view g1, g2, and g3 propagate within the light guide plate 30 along approximately the same path for both solid and dashed lines. In other words, dark and bright streaks can be suppressed.

[0073] For example, the reflection period of the image light with a field of view of g1 propagating within the light guide plate 30 is made equal to the width W11 of the image light with a field of view of g1 incident from the image light emission unit 50 to the first hologram element 41. In this case, if the thickness of the light guide plate 30 is T and the θm of the image light with a field of view of g1 is θm(-fov), then the reflection period p1 of the image light with a field of view of g1 and the width W11 are 2T・tanθm(-fov).

[0074] Similarly, the reflection period of the image light with a field of view of g2 propagating within the light guide plate 30 is made equal to the width W12 of the image light with a field of view of g2 incident from the image light emission unit 50 to the first hologram element 41. In this case, if the thickness of the light guide plate 30 is T and the θm of the image light with a field of view of g2 is θm(ctr), then the reflection period p2 of the image light with a field of view of g2 and the width W12 are 2T・tanθm(ctr).

[0075] Furthermore, the reflection period of the image light with a field of view of g3 propagating within the light guide plate 30 is made equal to the width W13 of the image light with a field of view of g3 incident from the image light emission unit 50 to the first hologram element 41. In this case, if the thickness of the light guide plate 30 is T and the θm of the image light with a field of view of g3 is θm(+fov), then the reflection period p3 of the image light with a field of view of g3 and the width W13 are 2T・tanθm(+fov).

[0076] By controlling the aperture size and aperture position of each of the multiple second lenses 56a so as described above, the widths W11, W12, and W13 of the image light incident on the first hologram element 41 can be determined.

[0077] Figure 10 is an explanatory diagram showing the relationship between the aperture size of the second lens 56a and the transmitted light according to the embodiment. Figure 10(a) shows the second lens 56aa with an aperture size of 100%. The light transmitted through this second lens 56aa is focused once and then spreads out. The FOV (Field of View) of this second lens 56aa is set to +θ to -θ. The percentage relative to the aperture size indicates the size of the aperture. For example, when the aperture size is 100%, the aperture size of the second lens 56a is the same as the lens pitch, and when the aperture size is 50%, the aperture size of the second lens 56a is half the lens pitch. When the aperture size is 0%, it represents the line or surface of the inclination of the lens slope near 0%. In other words, even if the aperture size is 0%, the second lens 56a has a certain size.

[0078] Figure 10(b) shows the second lens 56ab with an aperture size of 75%, and the FOV of this second lens 56ab is +θ to -θ / 2. Figure 10(c) shows the second lens 56ac with an aperture size of 50%, and the FOV of this second lens 56ac is +θ to 0. Figure 10(d) shows the second lens 56ad with an aperture size of 25%, and the FOV of this second lens 56ad is +θ to +θ / 2. Figure 10(e) shows the second lens 56ae with an aperture size of 0%, and the FOV of this second lens 56ae is +θ. Each of the second lenses 56aa to 56ae transmits only light near the FOV. In this way, the width of the image light can be adjusted by combining second lenses 56aa to 56ae with different aperture sizes.

[0079] Figure 11 is a cross-sectional view showing an example of a second optical body 56 according to an embodiment. As shown in Figure 11, in the second optical body 56, the multiple second lenses 56aa arranged in the central part have an aperture size of 100%. In this 100% area, light is transmitted when the FOV is between +θ and -θ. Outside the first range (100% area), the second lens 56ab is arranged, then the second lens 56ac is arranged outside of that, then the second lens 56ad is arranged outside of that, and then the second lens 56ae is arranged outside of that. The further you go from the 100% area, the smaller the aperture size becomes. In other words, light with an FOV near +θ has a wide range, and light with an FOV between +θ and -θ has a narrow range. In this way, by controlling the aperture size and aperture position of each of the multiple second lenses 56a, the width of the image light incident on the first hologram element 41 can be determined.

[0080] The multiple second lenses 56a have different lens thicknesses as the aperture size changes. In the example in Figure 11, the lens thickness of the second lens 56a increases as the aperture size of the second lens 56a changes from the first range toward the right in the drawing. Conversely, the lens thickness of the second lens 56a decreases as the aperture size of the second lens 56a changes from the first range toward the left in the drawing.

[0081] <Effects, etc.> As described above, according to the above embodiment, the image light emitting unit 50 varies the width of the image light incident on the first hologram element 41 based on the field of view of the image light, so that dark streaks and bright streaks are suppressed and the quality of the image projected onto the front windshield 3 is improved.

[0082] Furthermore, since the reflection periods p1, p2, and p3 of the image light propagating within the light guide plate 30 are equivalent to the widths W11, W12, and W13 of the image light incident from the image light emission unit 50 to the first hologram element 41, dark and bright streaks appearing in the image can be suppressed more reliably.

[0083] Furthermore, the widths W11, W12, and W13 of the image light incident on the first hologram element 41 are determined by controlling the aperture size and aperture position of each of the multiple second lenses 56a (microlenses) provided in the second optical body 56 (microlens array). Therefore, the widths W11, W12, and W13 of the image light incident on the first hologram element 41 can be determined by the second optical body 56 alone, and can be realized with a simple structure.

[0084] (Other) The display devices relating to this disclosure have been described above based on the embodiments described above, but this disclosure is not limited to these embodiments. Various modifications to the embodiments that a person skilled in the art can conceive of may also be included in the scope of this disclosure, as long as they do not depart from the spirit of this disclosure.

[0085] Furthermore, this disclosure also includes forms that can be obtained by applying various modifications to the above embodiments that a person skilled in the art could conceive, as well as forms that can be realized by arbitrarily combining the components and functions of the embodiments without departing from the spirit of this disclosure.

[0086] (Note) The features of the display device described based on the above embodiment are shown below.

[0087] <Technology 1> A display device comprising: an image light emitting unit that outputs image light; and a light guide plate comprising a hologram element into which the image light emitted by the image light emitting unit is incident, and a light guide unit that encloses the hologram element, wherein the hologram element comprises an incident hologram element into which the image light is incident, and the image light emitting unit causes the width of the image light incident on the incident hologram element to vary based on the field of view of the image light.

[0088] <Technology 2> The display device according to Technology 1, wherein the reflection period of the image light propagating within the light guide plate is equal to the width of the image light incident from the image light emission unit to the incident hologram element.

[0089] <Technology 3> The display device according to Technology 2, wherein the image light emitting unit comprises a microlens array positioned optically conjugate to the incident hologram element, the microlens array comprises a plurality of microlenses arranged in an array, and the width of the image light incident on the incident hologram element is determined by controlling the aperture size and aperture position of each of the plurality of microlenses.

[0090] This disclosure can be used in vehicle head-up display devices, etc.

[0091] 1 Display device 2 Vehicle 3 Front windshield 30 Light guide plate 31 Light guide section 31a Incident surface 31b Emitting surface 40 Hologram element 41, 41a First hologram element (incident hologram element) 42 Second hologram element 43 Third hologram element 50 Image light emission section 51 Light source 51a First light source 51b Second light source 51c Third light source 52 Lens 53 Reflector 53a First reflector 53b Second reflector 53c Third reflector 54 First optical body 55 Collimating lens 56 Second optical body 56a, 56aa, 56ab, 56ac, 56ad, 56ae Second lens 56a1 Second incident surface 56a2 Second emitting surface 57a Field lens 57b Projection lens 58 Polarizing beam splitter 59 Image display elements g1, g2, g3 Field of view p1, p2, p3 Reflection period W1, W2, W3, W11, W12, W13 Width

Claims

1. A display device comprising: an image light emitting unit that outputs image light; and a light guide plate having a hologram element into which the image light emitted by the image light emitting unit is incident, and a light guide unit enclosing the hologram element, wherein the hologram element comprises an incident hologram element into which the image light is incident, and the image light emitting unit causes the width of the image light incident on the incident hologram element to vary based on the field of view of the image light.

2. The display device according to claim 1, wherein the reflection period of the image light propagating within the light guide plate is equal to the width of the image light incident from the image light emission unit to the incident hologram element.

3. The display device according to claim 2, wherein the image light emitting unit comprises a microlens array positioned optically conjugate to the incident hologram element, the microlens array comprises a plurality of microlenses arranged in an array, and the width of the image light incident on the incident hologram element is determined by controlling the aperture size and aperture position of each of the plurality of microlenses.

Images