Head-up display

Abstract

To provide a head-up display that enables suppressing a fall of luminance of a virtual image while keeping a three-dimensional feeling of the virtual image.SOLUTION: A fluorescence detector comprises: a display panel that irradiates light to project images inside of a housing; a first mirror that causes the light transmitting the display panel to reflect; and a half mirror that is provided between the display panel and the first mirror. The half mirror includes a cholesteric liquid crystal layer transmitting the light from the display panel, and reflecting the light from the first mirror, and an angle formed with a face transmitting the light from the display panel of the half mirror, and a face irradiating the light from the display panel of the display panel is an acute angle.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a head-up display.

Background Art

[0002] As one of display devices, a head-up display (hereinafter referred to as HUD: Head Up Display) that projects an image onto a light-transmitting body such as a front glass and allows a user to visually recognize a virtual image is known (for example, Patent Document 1). By tilting a transmissive liquid crystal panel provided on the optical axis of the projected light with respect to a direction perpendicular to the optical axis, the three-dimensional effect of the virtual image can be made more prominent.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, simply tilting the liquid crystal panel with respect to a direction perpendicular to the optical axis reduces the brightness of the virtual image. Therefore, there has been a demand for a method of making the three-dimensional effect of the virtual image more prominent while suppressing a decrease in the brightness of the virtual image.

[0005] The present disclosure has been made in view of the above problems, and an object thereof is to provide a head-up display capable of suppressing a decrease in the brightness of a virtual image while maintaining the three-dimensional effect of the virtual image.

Means for Solving the Problems

[0006] A head-up display according to one aspect of the present disclosure comprises a display panel that transmits light and projects an image, a mirror that refracts the light transmitted through the display panel, and a half-mirror provided between the display panel and the mirror, wherein the half-mirror includes a cholesteric liquid crystal layer that transmits light from the display panel and reflects the light refracted by the mirror. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic diagram showing an example of the HUD configuration according to Embodiment 1. [Figure 2] Figure 2 is a schematic cross-sectional view illustrating the cholesteric liquid crystal layer of Embodiment 1. [Figure 3] Figure 3 is a schematic plan view illustrating the first and seventh layers of the cholesteric liquid crystal layer in Embodiment 1. [Figure 4] Figure 4 is a schematic plan view illustrating the second layer of the cholesteric liquid crystal layer in Embodiment 1. [Figure 5] Figure 5 is a schematic plan view illustrating the third layer of the cholesteric liquid crystal layer in Embodiment 1. [Figure 6] Figure 6 is a schematic plan view illustrating the fourth layer of the cholesteric liquid crystal layer in Embodiment 1. [Figure 7] Figure 7 is a schematic plan view illustrating the fifth layer of the cholesteric liquid crystal layer in Embodiment 1. [Figure 8] Figure 8 is a schematic plan view illustrating the sixth layer of the cholesteric liquid crystal layer in Embodiment 1. [Figure 9] Figure 9 is an explanatory diagram illustrating the relationship between incident light and reflected light. [Figure 10] Figure 10 is a schematic diagram showing an example of the HUD configuration according to Embodiment 2. [Figure 11] Figure 11 is a schematic diagram showing an example of the HUD configuration according to Embodiment 3. [Figure 12] Figure 12 is an enlarged schematic diagram of Figure 11. [Figure 13]Figure 13 is a schematic diagram showing an example of the HUD configuration according to Embodiment 4. [Figure 14] Figure 14 is a schematic diagram showing an example of the HUD configuration according to Embodiment 5. [Figure 15] Figure 15 is a schematic cross-sectional view illustrating the cholesteric liquid crystal layer of Embodiment 5. [Figure 16] Figure 16 is a schematic diagram showing an example of the HUD configuration according to Embodiment 6. [Figure 17] Figure 17 is a schematic diagram showing an example of the HUD configuration according to Embodiment 7. [Figure 18] Figure 18 is a schematic diagram showing an example of the HUD configuration according to Embodiment 8. [Figure 19] Figure 19 is a schematic diagram showing an example of the HUD configuration according to Comparative Example 1. [Figure 20] Figure 20 is a schematic diagram showing an example of the HUD configuration according to Embodiment 9. [Modes for carrying out the invention]

[0008] The embodiments of this disclosure will be described below with reference to the drawings. It should be noted 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 this disclosure. Furthermore, the drawings may schematically represent the width, thickness, shape, etc., of parts in order to clarify the explanation, but these are merely examples and do not limit the interpretation of this disclosure. In addition, in this specification and the drawings, 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.

[0009] (Embodiment 1) FIG. 1 is a schematic diagram showing a configuration example of the HUD according to Embodiment 1. FIG. 2 is a cross-sectional view schematically explaining the cholesteric liquid crystal layer of Embodiment 1. FIG. 3 is a plan view schematically explaining the first layer and the seventh layer of the cholesteric liquid crystal layer of Embodiment 1. FIG. 4 is a plan view schematically explaining the second layer of the cholesteric liquid crystal layer of Embodiment 1. FIG. 5 is a plan view schematically explaining the third layer of the cholesteric liquid crystal layer of Embodiment 1. FIG. 6 is a plan view schematically explaining the fourth layer of the cholesteric liquid crystal layer of Embodiment 1. FIG. 7 is a plan view schematically explaining the fifth layer of the cholesteric liquid crystal layer of Embodiment 1. FIG. 8 is a plan view schematically explaining the sixth layer of the cholesteric liquid crystal layer of Embodiment 1.

[0010] As shown in FIG. 1, the HUD 100 includes a display panel 10, a first quarter-wave plate 20, a half mirror 30, and a first mirror 40. Hereinafter, the height direction of the HUD is defined as the Dx direction. Also, the width direction of the HUD is defined as the Dy direction, and the depth direction of the HUD is defined as the Dz direction. Note that the directions of Dx, Dy, and Dz are merely examples, and the present disclosure is not limited to these directions.

[0011] The display panel 10 is a so-called liquid crystal display panel (LCD: Liquid Crystal Display). The display panel 10 is projected onto a projection member FG (for example, a front glass) of an image by the HUD 100, and allows the user U to visually recognize a virtual image VG. The projection member FG is not limited to a front glass, and may be, for example, a windshield or a translucent plate member called a combiner provided separately from the front glass. On the back surface of the display panel 10, there are a plurality of light-emitting elements (not shown), which function as a light source that irradiates light from the back side of the display panel 10. The light-emitting element is, for example, an LED (Light Emitting Diode), but is not limited thereto, and other configurations that function similarly, for example, an organic light-emitting diode (OLED: Organic Light Emitting Diode) may also be used. The light-emitting element 85 may be an inorganic light-emitting diode (micro LED, mini LED).

[0012] As shown in FIG. 1, light is irradiated from the display panel 10, and the light transmitted through the half mirror 30 from the display panel 10 is shown as light L4, light C4, and light U4, respectively.

[0013] The first quarter-wave plate 20 converts the linearly polarized light irradiated from the display panel 10 into circularly polarized light.

[0014] As shown in FIG. 1, the half mirror 30 includes a cholesteric liquid crystal layer 30a that transmits the light irradiated from the display panel 10 and reflects the light reflected from the first mirror 40. The half mirror 30 is disposed on the front side of the vehicle rather than the projection member FG. In the Dx direction, the half mirror 30 is disposed between the display panel 10 and the half mirror 30. The angle α formed by the surface 31 of the half mirror 30 that transmits light from the display panel 10 and the surface 11 of the display panel 10 that irradiates light to the half mirror 30 is an acute angle.

[0015] As shown in FIG. 2, in the cholesteric liquid crystal layer 30a, a liquid crystal layer 16 is formed on a light-transmissive substrate 14 via an alignment film 15. The alignment film 15 is made of polyimide or the like and is subjected to rubbing treatment or photo-alignment treatment. Cholesteric liquid crystal means that in one plane, elongated liquid crystal molecules are arranged with their long axis directions aligned, and as they proceed in a direction perpendicular to the plane of the light-transmissive substrate 14, the liquid crystal molecules LC turn in a spiral shape. Specifically, as shown in FIG. 2, the first layer LC1, the second layer LC2, the third layer LC3, the fourth layer LC4, the fifth layer LC5, the sixth layer LC6, and the seventh layer LC7 shown in FIG. 2 have the liquid crystal molecules LC turning as shown in FIGS. 3 to 9. Since the long axis directions of the liquid crystal molecules LC are aligned every half of the pitch p of the spiral, as shown in FIG. 3, the long axis direction of the liquid crystal molecules LC in the first layer LC1 and the long axis direction of the liquid crystal molecules LC in the seventh layer LC7 are the same direction.

[0016] Figure 9 is an explanatory diagram illustrating the relationship between incident and reflected light. The cholesteric liquid crystal layer 30a reflects light of a predetermined wavelength having circular polarization in the same direction of rotation as the helix. As shown in Figure 9, the incident light L11 incident on the cholesteric liquid crystal layer 30a is reflected according to the same conditions as Bragg's law shown in equation (1).

[0017]

number

[0018] As shown in Figure 9, according to Bragg's law, the incident light L11 is selectively reflected to become reflected light L12. For example, in the case of the cholesteric liquid crystal layer 30a, when multiple liquid crystal molecules are orbiting clockwise, the right-circularly polarized light from the incident light L11 having a wavelength corresponding to the pitch p is reflected to become reflected light L12. On the other hand, in the case of the cholesteric liquid crystal layer 10, when multiple liquid crystal molecules are orbiting counterclockwise, the left-circularly polarized light from the incident light L11 having a wavelength corresponding to the pitch p is reflected to become reflected light L12. This embodiment will be explained in the case where multiple liquid crystal molecules are orbiting counterclockwise.

[0019] The cholesteric liquid crystal layer 30a is manufactured by selecting liquid crystal material and chiral agent according to the wavelength of the incident light.

[0020] The first mirror 40 is an optical element that reflects light transmitted through the half mirror 30 from the display panel 10 towards the half mirror 30. The first mirror 40 is located below the half mirror 30. Here, the light L4 reflected by the first mirror 40 is shown as light L3. Also, the light C4 reflected by the first mirror 40 is shown as light C3. Also, the light U4 reflected by the first mirror 40 is shown as light U3.

[0021] As shown in Figure 1, the light L3 reflected by the half-mirror 30 is shown as light L2. Similarly, the light C3 reflected by the half-mirror 30 is shown as light C2. Furthermore, the light U3 reflected by the half-mirror 30 is shown as light U2.

[0022] The HUD100 further comprises a second mirror 50 and a housing CA. The second mirror 50 reflects light transmitted from the cholesteric liquid crystal layer 30a and guides it to the projection member FG. The housing CA surrounds the display panel 10, the first quarter-wave plate 20, the half mirror 30, the first mirror 40, and the second mirror 50. However, the housing CA is provided with an opening AP so as not to block the light path between the second mirror 50 and the projection member FG. As shown in Figure 1, the light reflected by the second mirror 50, passing through the opening AP and guided to the projection member FG is shown as light L1, C1, and U1. Light L1 is light L2 reflected by the second mirror 50 and projected onto the projection point PP1 of the projection member FG. Light C1 is light C2 reflected by the second mirror 50 and projected onto the projection point PP2 of the projection member FG. Light U1 is light U2 that is reflected by the second mirror 50 and projected onto the projection point PP3 of the projection member FG.

[0023] The second mirror 50 is, for example, a concave mirror. Alternatively, the second mirror 50 may be composed of multiple concave mirrors and reflecting mirrors.

[0024] The projection member FG is a translucent member provided on the exterior of the housing CA. The projection member FG is, for example, the windshield of a four-wheeled vehicle. The projection member FG of the image from the HUD 100 may be made of a translucent resin. Furthermore, the projection member FG may be a flat translucent member or a curved translucent member.

[0025] As shown in Figure 9, the clockwise circularly polarized light U4 entering the half mirror 30 from the display panel 10 passes through the half mirror 30 and enters the first mirror 40. The light U3 reflected from the first mirror 40 has its circular polarization direction reversed to counterclockwise and enters the half mirror 30. The light U2 reflected from the half mirror 30 enters the second mirror 50 as counterclockwise circularly polarized light. The light U1 reflected from the second mirror 50 is projected onto the projection point PP3 of the projection member FG as counterclockwise circularly polarized light.

[0026] The image projected from the HUD100 onto the projection target FG is recognized by the user U as a virtual image VG. As shown in Figure 1, the color and brightness of the light at the virtual image point VP1 of the virtual image VG correspond to the color and brightness of the light projected onto the projection point PP1. Similarly, the color and brightness of the light at the virtual image point VP2 of the virtual image VG correspond to the color and brightness of the light projected onto the projection point PP2. Furthermore, the color and brightness of the light at the virtual image point VP3 of the virtual image VG correspond to the color and brightness of the light projected onto the projection point PP3.

[0027] Furthermore, the relative positions of the virtual image points VP1, VP2, and VP3 recognized by user U, particularly their relative positions in the Dz direction, correspond to the respective optical path lengths of optical U2, C2, and L2, and optical U1, C1, and L1.

[0028] The distance (z1) between the user U's viewpoint and the virtual image point VP1 corresponds to the following equation (1). In equation (1), t1 is a value indicating the optical path length of optical U2. In equation (1), r1 is a value indicating the optical path length of optical U1. In equation (1), as well as in equations (2) and (3) described later, Ex indicates the magnification of the image produced by the optical path length between the half mirror 30 and the projection target member FG. z1 = r1 + t1 × Ex ... (1)

[0029] The distance (z2) between user U's viewpoint and the virtual image point VP2 corresponds to equation (2) below. In equation (2), t2 is a value indicating the optical path length of optical C2. In equation (2), r2 is a value indicating the optical path length of optical C1. z² = r² + t² × Ex…(2)

[0030] The distance (z3) between user U's viewpoint and the virtual image point VP3 corresponds to the following equation (3). In equation (3), t3 is a value indicating the optical path length of optical fiber L2. In equation (3), r3 is a value indicating the optical path length of optical fiber L1. z³ = r³ + t³ × Ex…(3)

[0031] Since the surface 11 of the display panel 10 that illuminates the half mirror 30 and the surface 41 of the first mirror 40 that reflects light to the half mirror 30 are horizontal, the relative lengths of the optical path lengths of light L4, light C4, and light U4 are U4=C4=L4. At this time, the relative lengths of the optical path lengths of light L2, light C2, and light U2 are U2=C2=L2. Also, the relative lengths of the optical path lengths of light L1, light C1, and light U1 are U1=C1=L1. The relative lengths of the optical path lengths of light L3, light C3, and light U3 are U3>C3>L3, resulting in a difference in optical path lengths, which affects the depth of the virtual image VG and enhances the three-dimensional effect of the virtual image that the user U can perceive.

[0032] As a result, the surface 11 of the display panel 10 that illuminates the half mirror 30 does not need to be tilted relative to the surface 41 of the first mirror 40 that reflects light to the half mirror 30, and the HUD 100 can maintain the three-dimensionality of the virtual image while suppressing a decrease in the brightness of the virtual image.

[0033] (Embodiment 2) Figure 10 is a schematic diagram showing an example of the configuration of the HUD according to Embodiment 2. In the following description, the same reference numerals are used for components that are the same as those described in the above-described embodiment, and redundant explanations are omitted. Also, explanations of the optical path that are redundant with those of the HUD according to Embodiment 1 are omitted.

[0034] As shown in Figure 10, the HUD100A includes a light source 10, a display panel 10, a first quarter-wave plate 20, a half-mirror 30, a first mirror 40, and a second mirror 50 within the housing CA.

[0035] The half mirror 30 is positioned between the projection member FG and the second mirror 50 in the Dx direction. The half mirror 30 is positioned between the first mirror 40 and the display panel 10 in the Dz direction.

[0036] As shown in Figure 10, light L2, light C2, and light U2 are reflected by the second mirror 50 as light L1', light C1', and light U1', respectively, and then transmitted through the half mirror 30 and guided to the projection member FG.

[0037] As shown in Figure 10, the clockwise circularly polarized light U4 entering the half mirror 30 from the display panel 10 passes through the half mirror 30 and enters the first mirror 40. The light U3 reflected from the first mirror 40 has its circular polarization direction reversed to counterclockwise and enters the half mirror 30. The light U2 reflected from the half mirror 30 enters the second mirror 50 as counterclockwise circularly polarized light. The light U1' reflected from the second mirror 50 passes through the half mirror 30 and reaches the projected member FG as counterclockwise circularly polarized light, and is projected onto the projection point PP3 of the projected member FG.

[0038] Furthermore, the relative positions of the virtual image points VP1, VP2, and VP3 recognized by user U, particularly their relative positions in the Dx direction, correspond to the respective optical path lengths of optical U2, C2, and L2, and optical path lengths of optical U1', C1', and L1'.

[0039] The relative lengths of the optical paths L1', C1', and U1' are U1' > C1' > L1'. Increasing the difference in optical path lengths increases the magnification Ex, which affects the depth of the virtual image VG.

[0040] As a result, the HUD100A can maintain the three-dimensionality of the virtual image while suppressing the decrease in the brightness of the virtual image.

[0041] (Embodiment 3) Figure 11 is a schematic diagram showing an example of the HUD configuration according to Embodiment 3. Figure 12 is an enlarged schematic diagram of Figure 11. In the following description, the same reference numerals are used for components that are the same as those described in the above-described embodiments, and redundant explanations are omitted. Also, regarding the optical path, explanations that overlap with those of the HUD according to Embodiment 2 are omitted.

[0042] As shown in Figure 11, the HUD100B includes a display panel 10, a first quarter-wave plate 20, a half-mirror 30, a first mirror 40, and a second mirror 50 within the housing CA.

[0043] The first mirror 40 is positioned behind the half mirror 30 with respect to the Dz direction. The display panel 10 is positioned in front of the first mirror 40. The half mirror 30 is provided between the first mirror 40 and the display panel 10 with respect to the Dz direction.

[0044] The relative lengths of the optical paths L2+L3, C2+C3, and U2+U3 are U2+U3 > C2+C3 > L2+L3, resulting in a difference in optical path length.

[0045] As a result, the HUD100B can maintain the three-dimensionality of the virtual image while suppressing the decrease in the brightness of the virtual image.

[0046] As shown in Figure 12, the half mirror 30 is the throwing shadow The angle β between the surface 31 that reflects light to member FG and the surface 11 of the display panel 10 that emits light from the display panel is 0° or acute. The angle between the optical path lengths of light L2, light C2, and light U2 and the Bragg surface BL formed by the liquid crystal molecules LC of the half mirror 30 can be set to any angle such that the angle between the optical path lengths of light L2, light C2, and light U2 and the optical path lengths of light L3, light C3, and light U3 is 90° by continuously changing the orientation pitch of the liquid crystal molecules LC on the Bragg surface BL.

[0047] This ensures that the light reflected by the half-mirror 30 is reliably focused onto the second mirror 50, thereby suppressing scattering.

[0048] (Embodiment 4) Figure 13 is a schematic diagram showing an example of the configuration of the HUD according to Embodiment 4. In the following description, the same reference numerals are used for components that are the same as those described in the embodiments described above, and redundant explanations are omitted. Also, explanations of the optical path that are redundant with those of the HUD according to Embodiment 1 are omitted.

[0049] As shown in Figure 13, the HUD100C includes a display panel 10, a first quarter-wave plate 20, a half-mirror 30, a first mirror 40, a third mirror 42, and a second mirror 50 within the housing CA.

[0050] The first mirror 40 is positioned above the half mirror 30 with respect to the Dx direction. The third mirror 42 is positioned in front of the half mirror 30 with respect to the Dz direction.

[0051] The half mirror 30 is positioned on the front side of the vehicle relative to the projection member FG. The half mirror 30 is located between the first mirror 40 and the display panel 10 in the Dx direction. The half mirror 30 is located between the third mirror 42 and the second mirror 50 in the Dy direction.

[0052] As shown in Figure 13, the third mirror 42 is an optical element that reflects light reflected by the first mirror 40 through the half mirror 30 back to the half mirror 30. Here, the light L3 reflected toward the third mirror 42 is shown as light L3'. Similarly, the light C3 reflected toward the third mirror 42 is shown as light C3'. And the light U3 reflected toward the third mirror 42 is shown as light U3'.

[0053] As shown in Figure 13, of the light L3', the light that is transmitted through the cholesteric liquid crystal layer 30a by the third mirror 42 and guided to the second mirror 50 is shown as light L2. Also, of the light C3', the light that is transmitted through the half mirror 30 by the third mirror 42 and guided to the second mirror 50 is shown as light C2. Furthermore, of the light U3', the light that is transmitted through the half mirror 30 by the third mirror 42 and guided to the second mirror 50 is shown as light U2.

[0054] As shown in Figure 13, light L2, light C2, and light U2 are reflected by the second mirror 50 as light L1, light C1, and light U1, respectively, and are transmitted through the half mirror 30 and guided to the projection member FG.

[0055] As shown in Figure 13, the right-handed circularly polarized light U4 entering the half mirror 30 from the display panel 10 passes through the half mirror 30 and enters the first mirror 40. The light U3 reflected from the first mirror 40 has its circular polarization direction reversed to counterclockwise and enters the half mirror 30. The light U3' reflected from the half mirror 30 is reflected from the third mirror 42 as counterclockwise circularly polarized light. The light U2 reflected from the third mirror 42 has its circular polarization direction reversed to clockwise and enters the second mirror 50. The light U1 reflected from the second mirror 50 passes through the half mirror 30 and reaches the projection target FG as right-handed circularly polarized light, and is projected onto the projection point PP3 of the projection target FG.

[0056] The relative lengths of the optical path lengths between the first mirror 40, the third mirror 42, and the half mirror 30 are U3 + U3' = C3 + C3' = L3 + L3'. In this case, the relative lengths of the optical path lengths of light L2, light C2, and light U2 are U2 = C2 = L2. Also, the relative lengths of the optical path lengths of light L1, light C1, and light U1 are U1 = C1 = L1. Here, the relative lengths of the optical path lengths of light L2, light C2, and light U2 are U2 > C2 > L2. Because two mirrors are used, the difference in optical path lengths can be made larger, the magnification Ex increases, and this affects the depth of the virtual image VG.

[0057] This allows the HUD100C to maintain the three-dimensionality of the virtual image while suppressing the decrease in the brightness of the virtual image.

[0058] Furthermore, by sliding the display panel 10, half mirror 30, and first mirror 40 set toward the second mirror 50 in the Dz direction while maintaining the difference in optical path length, the components within the housing CA can be made more space-saving.

[0059] (Embodiment 5) Figure 14 is a schematic diagram showing an example of the configuration of the HUD according to Embodiment 5. Figure 15 is a schematic cross-sectional view illustrating the cholesteric liquid crystal layer of Embodiment 5. Figure 16 is a schematic cross-sectional view illustrating the Bragg surface in the cholesteric liquid crystal layer of Embodiment 5. In the following description, the same reference numerals are used for components that are the same as those described in the above embodiments, and redundant explanations are omitted. Also, regarding the optical path of light, explanations that are redundant with those of the HUD according to Embodiment 1 are omitted.

[0060] As shown in Figure 14, the HUD100D includes a display panel 10, a first quarter-wave plate 20, a half-mirror 30, and a first mirror 40 within the housing CA.

[0061] As shown in Figure 14, the half mirror 30 is positioned below the projection member FG in the Dx direction. The half mirror 30 is also provided between the first mirror 40 and the display panel 10 in the Dz direction.

[0062] As shown in Figure 14, light L3, light C3, and light U3 are reflected by the half mirror 30 as light L1, light C1, and light U1, respectively, and guided to the projection member FG.

[0063] Furthermore, the relative positions of the virtual image points VP1, VP2, and VP3 recognized by user U, particularly their relative positions in the Dz direction, correspond to the respective optical path lengths of optical U3, C3, and L3, and optical path lengths of optical U1, C1, and L1.

[0064] As shown in Figure 14, the clockwise circularly polarized light U4 incident from the display panel 10 to the half mirror 30 passes through the half mirror 30 and is incident on the first mirror 40. The light U3 reflected from the first mirror 40 has its circular polarization direction reversed to counterclockwise and is incident on the half mirror 30. The light U1 reflected from the half mirror 30 is projected as counterclockwise circularly polarized light onto the projection point PP3 of the projection member FG via the half mirror 30.

[0065] As shown in Figure 15, the Bragg surface BL formed by the liquid crystal molecules LC of the cholesteric liquid crystal layer 30a can be made concave toward the projection member FG by continuously changing the orientation pitch of the liquid crystal molecules LC.

[0066] As a result, the cholesteric liquid crystal layer 30a can act like a concave mirror, eliminating the need for the second mirror 50 and allowing for a more space-saving design for the components within the housing CA.

[0067] Furthermore, since the optical paths of L4, C4, and U4 are each folded back from the first mirror 40 to the cholesteric liquid crystal layer 30a after passing through the cholesteric liquid crystal layer 30a, the optical path length is increased, the magnification Ex is increased, and the second mirror 50 can be made smaller.

[0068] (Embodiment 6) Figure 16 is a schematic diagram showing an example of the configuration of the HUD according to Embodiment 6. In the following description, the same reference numerals are used for components that are the same as those described in the embodiments described above, and redundant explanations are omitted. Also, explanations of the optical path that are redundant with those of the HUD according to Embodiment 5 are omitted.

[0069] As shown in Figure 16, the HUD100E includes a display panel 10, a first quarter-wave plate 20, a half-mirror 30, and a first mirror 40 within the housing CA. Here, the normal to the surface 11 of the display panel 10 that illuminates the half-mirror 30 is defined as the Z direction. The angle between the Z direction and the Dz direction is the polar angle θ, which is an acute angle.

[0070] As shown in Figure 16, the half mirror 30 is positioned below the projection member FG in the Dx direction. The surface 31 of the half mirror 30 that transmits light from the display panel 10 is positioned horizontally in the Dz direction. The half mirror 30 is also positioned between the first mirror 40 and the display panel 10 in the Z direction. The first mirror 40 is tilted with respect to the horizontal and is positioned on the front side of the vehicle relative to the projection member FG.

[0071] The relative lengths of the optical paths L4, C4, and U4 are U4=C4=L4. Here, the relative lengths of the optical paths L3, C3, and U3 are U3>C3>L3, and the relative lengths of the optical paths L1, C1, and U1 are U1>C1>L1. Therefore, the difference in optical paths can be maximized, which affects the depth of the virtual image VG.

[0072] This allows the HUD100E to maintain the three-dimensionality of the virtual image while suppressing the decrease in the brightness of the virtual image.

[0073] (Embodiment 7) Figure 17 is a schematic diagram showing an example of the configuration of the HUD according to Embodiment 7. In the following description, the same reference numerals are used for components that are the same as those described in the embodiments described above, and redundant explanations are omitted. Also, explanations of the optical path that are redundant with those of the HUD according to Embodiment 5 are omitted.

[0074] As shown in Figure 17, the HUD100F includes a display panel 10, a half mirror 30, and a first mirror 40 within the housing CA.

[0075] The half-mirror 30 is more resistant to impact than the cholesteric liquid crystal layer 30a. shadow An anti-reflective coating 33 is attached to the surface 32 on the FG side of the component. The anti-reflective coating 33 is, for example, an AR (Anti-Reflecton) film for preventing light reflection.

[0076] As a result, when L3, light C3, and light U3 are reflected from the first mirror 40 by the half mirror 30 and guided to the projected member FG as light L1, light C1, and light U1, respectively, surface reflection components generated from the surface 32 are suppressed, ghosting is eliminated, and the appearance of the virtual image is improved.

[0077] (Embodiment 8) Figure 18 is a schematic diagram showing an example of the HUD configuration according to Embodiment 8. In the following description, the same reference numerals are used for components that are the same as those described in the above-described embodiments, and redundant explanations are omitted. Also, explanations of the optical path that are redundant with those of the HUD according to Embodiment 5 are omitted.

[0078] As shown in Figure 18, the HUD100G includes a display panel 10, a first quarter-wave plate 20, a half-mirror 30, and a first mirror 40 within the housing CA.

[0079] The HUD100G further includes an absorbent member 60 on the lower side of the half mirror 30 with respect to the Dx direction.

[0080] As shown in Figure 18, the light L3 that is reflected by the half mirror 30 and incident toward the absorbing member 60 is shown as light L1''. Similarly, the light C3 that is reflected by the half mirror 30 and incident toward the absorbing member 60 is shown as light C1''. Furthermore, the light U3 that is reflected by the half mirror 30 and incident toward the absorbing member 60 is shown as light U1''.

[0081] The absorbing member 60 contains a dye that absorbs unwanted wavelengths of light. For example, the absorbing member 60 is preferably made of a black resin material, but it may also be made of black paper.

[0082] As shown in Figure 18, light U4 transmitted from the display panel 10 through the half mirror 30 enters the half mirror 30 as unpolarized light. In this case, only the corresponding circularly polarized light is reflected by the projection member FG and recognized by the user U as a HUD image.

[0083] Figure 19 is a schematic diagram showing a HUD according to Comparative Example 1. Compared to HUD100G shown in Figure 18, HUD100Ga of Comparative Example 1 does not have an absorbent member 60 on the lower side of the half mirror 30.

[0084] As shown in Figure 19, in the configuration of HUD100Ga of Comparative Example 1, when light L4, light C4, and light U4 are incident on the half mirror 30, circularly polarized light that matches the twist direction of the cholesteric liquid crystal layer 30a is reflected. As a result, the circularly polarized light L1'', C1'', and U1'' that are reflected from the first mirror 40 and transmitted through the half mirror 30 cannot be absorbed, and the circularly polarized light is scattered.

[0085] In contrast, in the configuration of HUD100G, since the absorbing member 60 is placed on the underside of the cholesteric liquid crystal layer 30a, scattering by light L4, light C4, and light U4 when they are incident on the half mirror 30 can be suppressed.

[0086] (Embodiment 9) Figure 20 is a schematic diagram showing an example of the HUD configuration according to Embodiment 9. In the following description, the same reference numerals are used for components that are the same as those described in the embodiments described above, and redundant explanations are omitted. Also, explanations of the optical path that are redundant with those of the HUD according to Embodiment 5 are omitted.

[0087] As shown in Figure 20, the HUD100H includes a display panel 10, a first quarter-wave plate 20, a half-mirror 30, and a first mirror 40 within the housing CA.

[0088] The HUD100H further has a second quarter-wave plate 21 directly below the opening AP between the half-mirror 30 and the projection member FG in the Dx direction.

[0089] The second quarter-wave plate 21 converts the light U1, light C1, and light L1 reflected from the half-mirror 30 from circularly polarized incident light to linearly polarized incident light.

[0090] As shown in Figure 19, user U views the image projected by HUD100H by wearing polarized sunglasses GL.

[0091] When user U is wearing polarized sunglasses GL, the virtual image VG becomes difficult to see if it remains circularly polarized. By inserting it into the second quarter-wave plate 21, the circular polarization is converted to linear polarization, improving visibility even when wearing polarized sunglasses.

[0092] Furthermore, any other effects and advantages brought about by the embodiments described above that are obvious from this specification or that can be appropriately conceived by a person skilled in the art are naturally provided by this disclosure. [Explanation of Symbols]

[0093] CA cabinet AP opening VG (Virtual Image) 100, 100A, 100B, 100C, 100D, 100E, 100F, 100G, 100H HUD 10 Display Panel 20 First quarter-wave plate 21 Second quarter-wave plate 30 Half Mirror 30a Cholesteric liquid crystal layer 40 First Mirror 42 Third Mirror 50 Second Mirror FG Projected member 60 Absorbing material GL Polarized Sunglasses

Claims

1. Inside the casing, A display panel that projects images by irradiating light, A first mirror that reflects light transmitted through the aforementioned display panel, The display panel and the first mirror are provided with a half-mirror, The half-mirror includes a cholesteric liquid crystal layer that transmits light from the display panel and reflects light from the first mirror. The surface of the half-mirror that transmits light from the display panel, The angle between the surface of the display panel from which light is emitted is acute. The cholesteric liquid crystal layer has liquid crystal molecules that spiral in a helical manner. The Bragg surface formed by the liquid crystal molecules is concave. Head-up display.

2. A first quarter-wave plate is provided between the display panel and the half-mirror, which causes the light from the display panel to be circularly polarized. The head-up display according to claim 1.

3. The exterior of the housing is provided with a light-transmitting projection member, Light from the first mirror is reflected by the half mirror and reaches the projection member, The surface of the half-mirror that transmits light from the display panel is arranged horizontally. The first mirror is tilted with respect to the horizontal. The head-up display according to claim 1 or 2.

4. The exterior of the housing is provided with a light-transmitting projection member, Light from the first mirror is reflected by the half mirror and reaches the projection member, The half-mirror has an anti-reflective coating on the side facing the projection member, rather than the cholesteric liquid crystal layer. The head-up display according to claim 1 or 2.

5. The exterior of the housing is provided with a light-transmitting projection member, A portion of the light from the first mirror is reflected by the half mirror and reaches the projection member. Furthermore, the system includes an absorbing member that absorbs circularly polarized light that has passed through the half-mirror, in addition to the light from the first mirror. The head-up display according to claim 1 or 2.

6. The exterior of the housing is provided with a light-transmitting projection member, A portion of the light from the first mirror is reflected by the half mirror and reaches the projection member. Furthermore, a second quarter-wave plate is provided between the half-mirror and the projection member. The head-up display according to claim 1 or 2.

Images