Indication device

Abstract

To provide a display device capable of improving efficiency in light utilization.SOLUTION: A display device includes an illumination device that emits illumination light, a display panel that modulates the illumination light and emits image light, a holographic optical element that reflects the image light emitted from the display panel, and a concave mirror that reflects the image light reflected by the holographic optical element. When the image light reflected by the concave mirror enters a projection member, a virtual image is projected. The holographic optical element reflects light incident at a specific angle of incidence on a Bragg reflection surface and transmits the light incident at an angle of incidence different from the specific angle of incidence.SELECTED DRAWING: Figure 5

Description

Technical Field

[0006]

[0001] Embodiments of the present invention relate to a display device.

Background Art

[0002] An optical system for observing a virtual image using a hologram has been developed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present embodiment is to provide a display device of a projection system using a holographic optical element, which can improve the light utilization efficiency.

Means for Solving the Problems

[0005] A display device according to an embodiment includes: a lighting device that emits illumination light; a display panel that modulates the illumination light and emits video light; [[ID=At47]] a holographic optical element that reflects the video light emitted from the display panel; a concave mirror that reflects the video light reflected by the holographic optical element; [[ID=5l]] and is provided with the video light reflected by the concave mirror is incident on a projection member, thereby projecting a virtual image. The holographic optical element reflects light incident at a specific incident angle with a Bragg reflection surface, and transmits light incident at an incident angle different from the specific incident angle.

Brief Description of the Drawings

[0006] [Figure 1] Figure 1 shows the basic configuration of the display device according to the embodiment. [Figure 2] Figure 2 shows a head-up display installed inside a vehicle. [Figure 3] Figure 3 shows the positional relationship between the virtual image and the windshield. [Figure 4] Figure 4 shows a part of the display device of the embodiment. [Figure 5] Figure 5 shows an example of a schematic configuration of the display device according to the embodiment. [Figure 6] Figure 6 is an enlarged view of a portion of Figure 5. [Figure 7] Figure 7 shows the positional relationship between the virtual image formed using the holographic optical element of the embodiment and the windshield. [Figure 8] Figure 8 shows an example of the configuration of a display device in an embodiment. [Figure 9] Figure 9 shows an example of the configuration of a display device in an embodiment. [Figure 10] Figure 10 is an enlarged view of a portion of Figure 9. [Figure 11] Figure 11 shows a head-up display of this configuration example installed inside a vehicle. [Figure 12] Figure 12 shows an example of the configuration of a display device in an embodiment. [Modes for carrying out the invention]

[0007] The embodiments of the present invention will be described below with reference to the drawings. Note that the disclosure is merely an example, and modifications that can be easily conceived by those skilled in the art while maintaining the spirit of the invention are naturally included within the scope of the present invention. Furthermore, in order to clarify the explanation, the drawings may schematically represent the width, thickness, shape, etc., of each part compared to the actual embodiment, but these are merely examples and do not limit the interpretation of the present invention. In addition, in this specification and in each drawing, elements similar to those described above in previously shown drawings are denoted by the same reference numerals, and detailed explanations may be omitted as appropriate. A display device according to one embodiment will be described in detail below with reference to the drawings.

[0008] In this embodiment, the first direction X, the second direction Y, and the third direction Z are orthogonal to each other, but they may intersect at angles other than 90 degrees. The direction toward the tip of the arrow in the third direction Z is defined as up or upward, and the direction opposite to the direction toward the tip of the arrow in the third direction Z is defined as down or downward. The first direction X, the second direction Y, and the third direction Z may also be referred to as the X direction, the Y direction, and the Z direction, respectively.

[0009] Furthermore, when referring to "the second member above the first member" and "the second member below the first member," the second member may be in contact with the first member or may be located away from the first member. In the latter case, a third member may be interposed between the first member and the second member. On the other hand, when referring to "the second member above the first member" and "the second member below the first member," the second member is in contact with the first member.

[0010] Furthermore, assuming that there is an observation position for observing the display device on the tip side of the arrow in the third direction Z, viewing from this observation position toward the XY plane defined by the first direction X and the second direction Y is called a planar view. Viewing a cross-section of the display device in the XZ plane defined by the first direction X and the third direction Z, or in the YZ plane defined by the second direction Y and the third direction Z, is called a cross-sectional view.

[0011] [Embodiment] FIG. 1 is a diagram showing the basic configuration of the display device of the embodiment. The display device is mainly a display device for projecting an image onto the front windshield WSD of a vehicle, that is, an in-vehicle display device. More specifically, the display device of the embodiment is, for example, an in-vehicle head-up display (HUD).

[0012] The head-up display HUD shown in FIG. 1 includes an illumination device ILD, a display panel PNL, and a concave mirror CMR. The illumination device ILD includes a plurality of light source elements and illuminates the display panel PNL. The light emitted from the illumination device ILD is defined as illumination light ILL. The illumination light ILL is emitted onto the display panel PNL. The display panel PNL is assumed to be inclined at an angle α1 with respect to the third direction Z. The illumination device ILD is similarly inclined. Therefore, the illumination device ILD and the display panel PNL are arranged in parallel.

[0013] The display panel PNL of the present embodiment is a transmissive liquid crystal display panel. The light emitted from the display panel PNL is defined as video light IML. The display panel PNL is an optical modulation element that modulates the illumination light ILL from the illumination device ILD and emits the video light IML. However, the display panel PNL is not limited to the transmissive type and may be a reflective liquid crystal display panel.

[0014] Alternatively, the display panel PNL may be a display device using organic electroluminescence (EL), that is, a so-called OLED (Organic Light Emiting Device) display device. Further alternatively, it may be a display panel including self-emitting light-emitting elements such as micro LEDs and mini LEDs.

[0015] As described above, when projecting an image onto the vehicle front windshield WSD by the head-up display HUD, as shown in FIG. 2, it is necessary to install the head-up display HUD inside the vehicle VCL.

[0016] Figure 2 shows a head-up display installed inside a vehicle. The head-up display (HUD) is mounted on the instrument panel (INP) of the vehicle's VCL. As will be explained in more detail later, the head-up display (HUD) projects a virtual image (VTI) onto the windshield (WSD, also called the windscreen) of the vehicle's VCL. In Figure 2, the head-up display (HUD) is installed in front of the driver's seat where the steering wheel (WHL) is located. However, the installation location of the head-up display (HUD) is not limited to this.

[0017] If the display panel PNL is a transmissive display panel, the illumination device ILD is positioned on the rear side of the display panel PNL. As will be explained in detail later, a laser backlight is preferred for the illumination device ILD. On the other hand, if the display panel PNL is a reflective display panel, the display panel PNL displays an image by selectively reflecting illumination light ILL from the illumination device ILD. In this case, the illumination device ILD is positioned on the front side of the display panel PNL. That is, the illumination device ILD is a front light, not a backlight.

[0018] Returning to Figure 1, the concave mirror CMR is a component that reflects the image light IML (including image light IML1, IML2, and IML3 described later) emitted from the display panel PNL toward the windshield WSD.

[0019] The image light (IML) emitted from the head-up display (HUD) is projected onto the vehicle's windshield (WSD). The user DRV using the head-up display (HUD) can see the virtual image (VTI) in front of the windshield WSD. In the example shown in Figure 1, the windshield WSD is given as the projection member onto which the image light (IML) is projected, but it is not limited to this. Other members such as a combiner may be used instead of the windshield WSD.

[0020] The display panel PNL shown in Figure 1 is assumed to be tilted at an angle α1 with respect to the third direction Z. If the angle α1 is small, the virtual image VTI is fixed roughly along the third direction Z. Such a virtual image VTI has the problem of having less depth perception compared to the background viewed through the windshield WSD.

[0021] For example, if the virtual image VTI is an image for a vehicle's route guidance service, the user DRV needs to perceive depth information based on the virtual image VTI, which is roughly fixed in the third direction Z, relative to the background that extends horizontally (the direction in which the XY plane expands). Therefore, the virtual image VTI does not provide a natural sense of depth relative to the background. In order for the virtual image VTI to provide a more natural sense of depth, it is necessary to display the virtual image VTI in a position that matches the actual background.

[0022] Figure 3 shows the positional relationship between the virtual VTI image and the windshield when the angle α1 is small. The virtual VTI image shown in Figure 3 is an arrow indicating a left turn. However, because the depth perception of the virtual VTI image does not match that of the background, the virtual VTI image does not have a natural sense of depth. As mentioned above, in order for the virtual VTI image to have a more natural sense of depth, it is necessary to display the virtual VTI image in a position that matches the actual background.

[0023] To resolve the above problem, for example, the display panel PNL can be tilted with respect to the third direction Z. That is, the display panel PNL should be positioned so that the angle is greater than the angle α1.

[0024] Figure 4 shows a part of the display device of the embodiment. In the head-up display (HUD) shown in Figure 4, the illumination device (ILD) is omitted. The display panel (PNL) of the head-up display (HUD) shown in Figure 4 is tilted by an angle α2 greater than angle α1 with respect to the third direction Z compared to Figure 1 (α2 > α1).

[0025] The image light IML1, IML2, and IML3 are image light emitted from the regions of the display panel PNL, corresponding to the upper region, central region, and lower region of the virtual image VTI, respectively. In Figure 4, the image light emitted from the lower region, central region, and upper region of the display panel PNL becomes the image light of the upper region, central region, and lower region of the virtual image VTI. In this embodiment, the regions of the display panel PNL corresponding to the upper region, central region, and lower region of the virtual image VTI are also referred to as the first region, second region, and third region. In Figure 4, the first region, second region, and third region are the lower region, central region, and upper region of the display panel PNL.

[0026] Image light emitted from the lower region of the display panel PNL and reaching the concave mirror CMR is designated as IML1b, and image light reflected by the concave mirror CMR and reaching the windshield WSD is designated as IML1a. Image light emitted from the central region of the display panel PNL and reaching the concave mirror CMR is designated as IML2b, and image light reflected by the concave mirror CMR and reaching the windshield WSD is designated as IML2a. Image light emitted from the upper region of the display panel PNL and reaching the concave mirror CMR is designated as IML3b, and image light reflected by the concave mirror CMR and reaching the windshield WSD is designated as IML3a. Image lights IML1, IML2, and IML3 are also referred to as the first image light, the second image light, and the third image light, respectively.

[0027] Image light IML1 is reflected by the concave mirror CMR, resulting in image light for the upper region of the virtual image VTI. Image light IML2 is reflected by the concave mirror CMR, resulting in image light for the region near the center of the virtual image VTI. Image light IML3 is reflected by the concave mirror CMR, resulting in image light for the lower region of the virtual image VTI.

[0028] In the image light IML1, the distance AD1 from the virtual image VTI to the windshield WSD is the sum of the distance LP1 from the concave mirror CMR to the windshield WSD, and the distance FP1 from the display panel PNL to the concave mirror CMR multiplied by the magnification mg of the concave mirror CMR. That is, AD1 = LP1 + (FP1 × mg) (Equation 1) holds true. Similarly, AD2 = LP2 + (FP2 × mg) (Equation 2) and AD3 = LP3 + (FP3 × mg) (Equation 3) hold true.

[0029] By increasing distance AD1 and decreasing distance AD3, the sense of depth of the virtual image VTI increases. The larger the angle α2, the longer distance AD1 and the shorter distance AD3 can be. To increase distance AD1, distance FP1 should be increased. To decrease distance AD3, distance FP3 should be decreased.

[0030] The principal rays of the image light from the display panel PNL are emitted in the direction normal to the display surface. Therefore, the more the display panel PNL is tilted, that is, the larger the angle α2 becomes, the smaller the proportion of the principal rays becomes in each of the image light IML1, IML2, and IML3. This may lead to deterioration of optical characteristics such as reduced brightness, reduced contrast, and worsened viewing angle characteristics.

[0031] In this embodiment of the head-up display (HUD), the image light emitted from the display panel (PNL) is emitted onto a concave mirror (CMR) via a holographic optical element. The holographic optical element is an optical element that reflects light incident at a specific angle of incidence on a Bragg reflecting surface and transmits light incident at an angle of incidence different from that specific angle. The holographic optical element in this embodiment is a volume hologram formed not only in the plane but also in the depth direction. By utilizing this, the principal rays of each image light can be reflected. This makes it possible to increase the distance AD1 and decrease the distance AD3 while maintaining brightness. Therefore, it is possible to give the virtual image VTI a sense of depth.

[0032] Figure 5 shows an example of a schematic configuration of the display device of the embodiment. The head-up display (HUD) shown in Figure 5 comprises a display panel (PNL), a holographic optical element (HOE), and a concave mirror (CMR). The display panel (PNL) and the holographic optical element (HOE) are arranged in parallel.

[0033] The image light IML1b, IML2b, and IML3b emitted from the display panel PNL are reflected by the holographic optical element HOE and reach the concave mirror CMR. The image light IML1b, IML2b, and IML3b are emitted from the display surface of the display panel PNL, corresponding to the upper region, the central region, and the lower region of the virtual image VTI, respectively.

[0034] The holographic optical element HOE reflects light incident at a specific angle of incidence on the Bragg reflector BR and transmits light incident at an angle of incidence different from that specific angle. The Bragg reflectors of the image light IML1b, IML2b, and IMLb are designated as Bragg reflectors BR1, BR2, and BR3, respectively.

[0035] Figure 6 is an enlarged view of a portion of Figure 5. In Figure 6, only the display panel PNL, the holographic optical element HOE, and the concave mirror CMR are shown. The image light emitted from the display panel PNL and reaching the holographic optical element HOE is denoted as image light IML1b1, IML2b1, and IML3b1. The image light reflected by the holographic optical element HOE and reaching the concave mirror CMR is denoted as image light IML1b2, IML2b2, and IML3b2.

[0036] Video light IML1b1 and IML1b2 correspond to video light IML1b. Video light IML2b1 and IML2b2 correspond to video light IML2b. Video light IML3b1 and IML3b2 correspond to video light IML3b.

[0037] The sum of the distances between video light sources IML1b1 and IML1b2 corresponds to distance FP1. The sum of the distances between video light sources IML2b1 and IML2b2 corresponds to distance FP2. The sum of the distances between video light sources IML3b1 and IML3b2 corresponds to distance FP3.

[0038] Let θ1, θ2, and θ3 be the angles formed by the plane HM of the holographic optical element HOE and the Bragg reflectors BR (BR1, BR2, and BR3), respectively.

[0039] The display panel PNL and the holographic optical element HOE are arranged in parallel. Furthermore, the holographic optical element HOE is a holographic optical element that reflects at a uniform angle within the plane. As a result, angles θ1, θ2, and θ3 are equal (θ1=θ2=θ3). Angles θ1, θ2, and θ3 are also referred to as the first angle, second angle, and third angle, respectively.

[0040] As shown in Figure 6, by arranging the display panel PNL and the holographic optical element HOE, the distance FP1 can be made longer and the distance FP3 shorter. In addition, the image light IML1b1, IML2b1, and IML3b1 are reflected by the Bragg reflectors BR1, BR2, and BR3, respectively, and emitted as image light IML1b2, IML2b2, and IML3b2. By being reflected by the Bragg reflectors, the brightness of each image light can be maintained when it reaches the concave mirror CMR.

[0041] The illumination device ILD of this embodiment preferably uses a laser backlight having multiple laser light source elements. The laser light source elements emit light with a predetermined wavelength as the main wavelength. The holographic optical element HOE has wavelength selectivity. If the wavelength selectively reflected by the holographic optical element HOE is set as the main wavelength of the laser light source element, the light incident on the holographic optical element HOE can be utilized efficiently. By using an illumination device ILD having laser light source elements, it is possible to obtain a virtual image VTI with high brightness.

[0042] Furthermore, it is preferable to apply an AR film to the holographic surface of the holographic optical element (HOE). By applying the AR film, surface reflection of the holographic optical element (HOE) can be prevented, making it possible to achieve good optical properties.

[0043] Figure 7 shows the positional relationship between the virtual image formed using the holographic optical element of the embodiment and the windshield. As explained in Figures 5 and 6, when distance FP1 is long and distance FP3 is short, distance AD1 is long and distance AD3 is short. Therefore, the virtual image VTI can obtain a sense of depth along with the background. In Figure 7, the arrow indicating a left turn in the virtual image VTI is an arrow that follows the sense of depth of the road. Thus, this embodiment makes it possible to increase the sense of depth of the virtual image VTI.

[0044] <Configuration Example 1> Figure 8 shows another example of the display device configuration in the embodiment. The configuration example shown in Figure 8 differs from the configuration example shown in Figure 6 in that the display panel and the holographic optical element are not arranged in parallel, and the angles between the plane of the holographic optical element and the Bragg reflector are different.

[0045] In the head-up display (HUD) shown in Figure 8, similar to the embodiment, the video light emitted from the lower region, central region, and lower region of the display panel PNL corresponds to the upper region, central region, and lower region of the virtual image VTI. The angles θ1, θ2, and θ3 formed by the video light IML1b (IML1b1 and IML1b2), IML2b (IML2b1 and IML2b2), and IML3b (IML3b1 and IML3b2) corresponding to the upper region, central region, and lower region of the virtual image VTI, and the planar HM of the holographic optical element HOE and the Bragg reflecting surface BR (BR1, BR2, and BR3) are in increasing order (θ1 < θ2 < θ3). In other words, angle θ3 is larger than angles θ1 and θ2, and angle θ2 is larger than angle θ1.

[0046] To change the angle at the Bragg reflecting surface BR, the holographic optical element HOE can be given the effect of a concave mirror.

[0047] By changing angles θ1, θ2, and θ3, the distances FP1, FP2, and FP3, which are the optical path distances of the image light IML1b, IML2b, and IML3b, can be changed. By making distance FP1 longer and distance FP3 shorter, the distance AD1 corresponding to image light IML1, which is the distance between the windshield WSD and the virtual image VTI, can be made longer, and the distance AD3 corresponding to image light IML3 can be made shorter. This makes it possible to increase the sense of depth of the virtual image VTI. This configuration example also achieves the same effects as the embodiment.

[0048] <Configuration Example 2> Figure 9 shows another example of the display device configuration in the embodiment. In the configuration example shown in Figure 9, the positional relationship between the display panel and the holographic optical element is different compared to the configuration example shown in Figure 5.

[0049] In Figure 5, the head-up display (HUD) is positioned between the windshield WSD and the user DRV. In contrast, in Figure 9, the head-up display (HUD) is not positioned between the windshield WSD and the user DRV. In Figure 9, the windshield WSD is positioned between the head-up display (HUD) and the user DRV.

[0050] The holographic optical element HOE shown in Figure 9 is positioned parallel to the display panel PNL. In Figure 9, the image light IML1, IML2, and IML3, corresponding to the upper, central, and lower regions of the virtual image VTI, are emitted from the upper, central, and lower regions of the display panel PNL, respectively.

[0051] Figure 10 is an enlarged view of a portion of Figure 9. In the head-up display (HUD) shown in Figure 10, similar to Figure 6, the angles θ1, θ2, and θ3 between the image light IML1b, IML2b, and IML3b emitted from the display panel PNL and the planar HM of the holographic optical element HOE and the Bragg reflectors BR1, BR2, and BR3 are equal (θ1=θ2=θ3).

[0052] Figure 11 shows the head-up display of this configuration example installed inside a vehicle. As explained in Figure 9, the windshield WSD is positioned between the head-up display (HUD) and the user DRV. In other words, the head-up display (HUD) shown in Figure 11 is housed in the area in front of the windshield WSD within the vehicle's VCL (Vehicle Center Room). By housing the space occupied by the head-up display (HUD) outside the vehicle's VCL rather than inside it, it is possible to increase the flexibility of the interior layout of the vehicle's VCL. This configuration example also achieves the same effects as the embodiment.

[0053] <Configuration Example 3> Figure 12 shows another example configuration of the display device in the embodiment. The configuration example shown in Figure 12 differs from the configuration example shown in Figure 10 in that the angles between the plane of the holographic optical element and the Bragg reflector are different. The holographic optical element HOE shown in Figure 12 is not positioned parallel to the display panel PNL, similar to Figure 8.

[0054] In the head-up display (HUD) shown in Figure 12, the angles θ1, θ2, and θ3 between the image light IML1b (IML1b1 and IML1b2), IML2b (IML2b1 and IML2b2), and IML3b (IML3b1 and IML3b2) emitted from the upper, central, and lower regions of the display panel PNL, and the plane HM of the holographic optical element HOE and the Bragg reflector BR, are in increasing order (θ1 < θ2 < θ3).

[0055] By changing angles θ1, θ2, and θ3, the distances FP1, FP2, and FP3, which are the optical path distances of the image light IML1b, IML2b, and IML3b, can be changed. By making distance FP1 longer and distance FP3 shorter, the distance AD1 corresponding to image light IML1, which is the distance between the windshield WSD and the virtual image VTI, can be made longer, and the distance AD3 corresponding to image light IML3 can be made shorter. This makes it possible to increase the sense of depth of the virtual image VTI. This configuration example also achieves the same effects as the embodiment.

[0056] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of symbols]

[0057] AD1...Distance, AD2...Distance, AD3...Distance, BR...Bragg reflective surface, DRV...User, FP1...Distance, FP2...Distance, FP3...Distance, HOE...Holographic optical element, HUD...Head-up display, ILD...Illumination device, IML...Image light, IML1...Image light, IML2...Image light, IML3...Image light, PNL...Display panel, BR...Bragg reflective surface, VCL...Vehicle, VTI...Virtual image, WSD...Windshield.

Claims

1. A lighting device that emits illumination light, A display panel that modulates the aforementioned illumination light to emit video light, A holographic optical element that reflects the image light emitted from the display panel, A concave mirror that reflects the image light reflected by the holographic optical element, Equipped with, When the image light reflected by the concave mirror enters the projection member, a virtual image is projected. The holographic optical element reflects light incident at a specific angle of incidence using a Bragg reflector and transmits light incident at an angle of incidence different from the specific angle of incidence. The first angle is defined as the angle formed between the first image light emitted from the first region of the display panel, the plane of the holographic optical element, and the Bragg reflecting surface. The second angle is defined as the angle formed between the second image light emitted from the second region of the display panel, the plane of the holographic optical element, and the Bragg reflecting surface. The third angle is defined as the angle between the third image light emitted from the third region of the display panel, the plane of the holographic optical element, and the Bragg reflecting surface. The first region, the second region, and the third region of the display panel correspond to the upper region, the central region, and the lower region of the virtual image, respectively. A display device in which the first, second, and third angles increase in that order.

2. The projection member is the windshield of the vehicle. The image light reflected by the concave mirror is incident on the windshield. The display device according to claim 1, wherein the user views the virtual image through the windshield when the aforementioned image light is projected.

3. The display device according to claim 2, provided between the windshield and the user.

4. The display device according to claim 2, wherein the windshield is provided between the display device and the user.

Images