Display device with variable mirror

Abstract

To reduce reflection of external light in an image display state of a display device with variable mirror.SOLUTION: A display device 1 with variable mirror capable of electrically switching between a mirror state and an image display state comprises: a display unit 10 which emits image light; a reflection type polarizing plate 11 which is arranged on the light-emitting side of the display unit; a liquid crystal lens 12 which is arranged so as to be opposed to the display unit with the reflection type polarizing plate held therebetween; and a control device which controls the operation of the display unit and the liquid crystal lens. The liquid crystal lens can be electrically switched between the first state that exhibits the lens action and the second state that does not exhibit the lens action by the control of the control device.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a display device with a deformable mirror. [Background technology]

[0002] As a conventional example of a display device with a variable mirror, for example, Japanese Patent Application Laid-Open No. 2021-138195 (Patent Document 1) describes a vehicle rearview mirror that can be switched at least between a mirror state and an image display state. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-138195 Summary of the Invention [Problem to be solved by the invention]

[0004] One object of a specific aspect of the present disclosure is to provide a technology capable of reducing reflection of external light in an image display state of a display device with a variable mirror that is switchable between a mirror state and an image display state. [Means for solving the problem]

[0005] A display device with a variable mirror according to one aspect of the present disclosure is a display device with a variable mirror that includes: (a) a display device with a variable mirror that can be electrically switched between a mirror state and an image display state, (b) a display unit that emits image light; (c) a reflective polarizing plate arranged on the light emission side of the display unit; (d) a liquid crystal lens arranged opposite the display unit across the reflective polarizing plate; and (e) a control device that controls the operation of the display unit and the liquid crystal lens; and (f) the liquid crystal lens can be electrically switched between a first state in which it exhibits a lens effect and a second state in which it does not exhibit the lens effect under the control of the control device.

[0006] According to the above configuration, it is possible to reduce reflection of external light in the image display state of the variable mirror-equipped display device that is switchable between a mirror state and an image display state. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram showing the configuration of a display device with a variable mirror according to an embodiment. [Figure 2] FIG. 2 is a diagram for explaining the operating principle of a liquid crystal lens. [Figure 3] 3(A) and 3(B) are diagrams for explaining the operation of the display device with a variable mirror. [Figure 4] 4(A) and 4(B) are diagrams for explaining the configuration and operation of a display device with a variable mirror according to a modified embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] FIG. 1 is a diagram showing the configuration of a display device with a variable mirror according to one embodiment. The display device with a variable mirror 1 shown in the figure includes a display unit 10, a reflective polarizing plate 11, a liquid crystal lens 12, a cover glass 13, and an anti-reflection film 14. The display unit 10 includes a backlight 10a, a pair of polarizing plates 10b and 10d, and a liquid crystal panel 10c. While FIG. 1 shows each component separated from one another for ease of understanding, in reality, each component is closely arranged with no gaps between them. This display device with a variable mirror 1 is used, for example, as a rearview mirror mounted in the passenger compartment of a vehicle, and can be freely switched between a function for displaying various images and a function as a mirror for the driver to check behind them.

[0009] The display unit 10 generates various images and emits light that constitutes the images (hereinafter referred to as "image light"). In the illustrated example, the display unit 10 has a liquid crystal panel 10c disposed between a pair of polarizing plates 10b and 10d, and a backlight 10a disposed on the polarizing plate 10b side. When planar light emitted from the backlight 10a enters the liquid crystal panel 10c, the light is appropriately modulated in the liquid crystal panel 10c and passes through the polarizing plate 10d to form image light.

[0010] In this embodiment, the transmission axis a1 of the polarizer 10b is substantially parallel to the X direction shown in the figure, and the transmission axis a2 of the polarizer 10d is substantially parallel to the Y direction perpendicular to the X direction. Each of the polarizers 10b and 10d is an absorption-type linear polarizer. The liquid crystal panel 10c is an active matrix liquid crystal panel that controls the voltage applied to a plurality of pixels arranged in a matrix by thin film transistors provided corresponding to each pixel.

[0011] The reflective polarizing plate 11 is disposed on the front side (light exit surface side) of the display unit 10. This reflective polarizing plate 11 may include, for example, a wire grid made of a large number of thin metal wires, or an optical multilayer film. In this embodiment, the transmission axis a3 of the reflective polarizing plate 11 is approximately parallel to the Y direction. Note that the reflective polarizing plate 11 may also function as the polarizing plate 10d, and the polarizing plate 10d may be omitted; however, using the reflective polarizing plate 11 and the polarizing plate 10d together can further improve the degree of polarization of the transmitted light.

[0012] The liquid crystal lens 12 is an element that can switch between a light-transmitting state and a lens state by applying a voltage. Various known liquid crystal lenses can be used as the liquid crystal lens 12, and for example, those described in known documents such as JP 2014-112157 A and JP 2018-101026 A can be used.

[0013] The cover glass 13 is a glass plate disposed on the front side (light-emitting surface side) of the liquid crystal lens 12 to protect the display unit 10, the liquid crystal lens 12, etc. The antireflection film 14 is disposed on the front side (light-emitting surface side) of the cover glass 13 and suppresses the reflection of external light by the cover glass 13. The control device 15 controls the operations of the backlight 10a, the liquid crystal panel 10c, and the liquid crystal lens 12.

[0014] The operating principle of the liquid crystal lens 12 will be described while referring to FIG. 2. In the example of the liquid crystal lens 12 shown in the figure, electrode 101a and electrode 101b are provided on substrate 90 and arranged with a gap therebetween, common electrode 102 is provided on substrate 91 and arranged opposite to each of electrode 101a and electrode 101b, and liquid crystal layer 103 is disposed between each of electrode 101a and electrode 101b and common electrode 102. Each of electrode 101a and electrode 101b is configured such that a voltage can be individually applied from the outside.

[0015] In the example of the liquid crystal lens 12 shown in the figure, for example, if voltage V1 is applied to electrode 101a and voltage V2 (<V1) is applied to electrode 101b, the alignment state of liquid crystal layer 103 can be changed to generate a refractive index distribution. In the example shown in the figure, since the electric field between electrode 101a and common electrode 102 is larger, the liquid crystal molecules of liquid crystal layer 103 that were horizontally aligned change their alignment more significantly in the vertical direction. The lens effect can be obtained in the portion where this refractive index distribution is generated. In the example shown in the figure, incident light L is deflected to the left side in the figure. This deflection angle can be controlled by the difference between voltage V1 and voltage V2. Also, if the magnitude relationship between voltage V1 and voltage V2 is reversed, the direction in which the incident light is deflected also becomes reversed. When no voltage is applied between each of electrode 101a and electrode 101b and common electrode 102, liquid crystal layer 103 becomes uniformly distributed and such a refractive index distribution does not occur. Therefore, the light transmission state and the lens state can be switched by the presence or absence of voltage application. Also, if the positions where each of electrode 101a and electrode 101b for forming the refractive index distribution are provided are changed, it is also possible to adjust the direction of refraction. If more electrodes are formed, various refractive index distributions can be generated.

[0016] The substrates 90 and 91 are each provided with an alignment film (not shown). The alignment treatment direction (e.g., rubbing treatment direction) a4 on the substrate 90 is, for example, rightward in the figure, and the alignment treatment direction (e.g., rubbing treatment direction) a5 on the substrate 91 is, for example, leftward in the figure. These alignment treatment directions a4 and a5 are arranged approximately parallel to the X direction in the coordinate system shown in FIG. 1 . Furthermore, the alignment treatment directions a4 and a5 are antiparallel to each other. As a result, light polarized in a direction approximately parallel to these alignment treatment directions a4 and a5 is subjected to the above-mentioned refraction action and its traveling direction is changed. On the other hand, light polarized in a direction approximately perpendicular to the alignment treatment directions a4 and a5 is not subjected to the refraction action and therefore its traveling direction is not changed. Here, the alignment treatment directions a4 and a5 of the liquid crystal lens 12 can be changed as appropriate depending on the device to which the display device with a variable mirror 1 is applied, its application, etc.

[0017] Figures 3(A) and 3(B) are diagrams for explaining the operation of the display device with a variable mirror 1. Note that in Figures 3(A) and 3(B), the cover glass 13, anti-reflection film 14, and control device 15 are omitted to make the operation easier to understand. Figure 3(A) shows the operation when performing the function of displaying various images, and Figure 3(B) shows the operation when performing the function of a mirror that allows the driver to check behind.

[0018] As shown in FIG. 3A, unpolarized light emitted from the backlight 10a and incident on the polarizer 10b is transmitted through the polarizer 10b, with the light component having the polarization direction a11, which is the same as the transmission axis a1, passing through the polarizer 10b and entering the liquid crystal panel 10c. In this embodiment, the polarization direction of the light incident on the liquid crystal panel 10c is rotated by 90° by the liquid crystal panel 10c, which is in the image display state (ON), and then the light enters the polarizer 10d. Because the polarization direction a12 of this light is approximately parallel to the transmission axis a2 of the polarizer 10d, the light passes through the polarizer 10d and enters the reflective polarizer 11. Because the transmission axis a3 of the reflective polarizer 11 is approximately parallel to the polarization direction a12, the light exits the reflective polarizer 11 unchanged. The light with the polarization direction a13 enters the liquid crystal lens 12. Because the polarization direction a13 of this light is approximately perpendicular to the alignment treatment directions a4 and a5 of the liquid crystal lens 12, the light exits without changing its direction of travel. The polarization direction a14 of the image light IML, which is light emitted from the liquid crystal lens 12, is approximately parallel to the Y direction in the drawing. A display image is formed by this image light IML.

[0019] Unpolarized external light EXL incident on liquid crystal lens 12 from the outside passes through liquid crystal lens 12 and enters reflective polarizer 11. Light polarized in the same direction as transmission axis a3 passes through reflective polarizer 11, then through polarizer 10d and liquid crystal panel 11c. This light that passes through liquid crystal panel 10c has a polarization direction that is approximately perpendicular to transmission axis a1 of polarizer 10b, and is therefore absorbed by polarizer 10b without reaching backlight 10a. Furthermore, light that enters reflective polarizer 11 and has a polarization direction that is approximately perpendicular to transmission axis a3 is reflected by reflective polarizer 11 and returns to liquid crystal lens 12. Because the polarization direction of this light is approximately parallel to the alignment treatment directions a4 and a5 of liquid crystal lens 12, it is refracted by liquid crystal lens 12, which is in a state (first state) that exhibits lens action when a voltage is applied, and is refracted at an angle θ before exiting liquid crystal lens 12. This angle θ can be, for example, 10° or more, depending on the configuration of the liquid crystal lens 12. That is, the reflected light of the external light EXL travels in an oblique direction rather than in the front direction of the display device 1 with a variable mirror.

[0020] In this embodiment, when planar light emitted from the backlight 10a enters the liquid crystal panel 10c as described above, this light is appropriately modulated by the liquid crystal panel 10c and passes through the polarizer 10d, thereby forming image light by the display unit 10. This image light passes through the reflective polarizer 11 as is and then passes through the liquid crystal lens 12 as is to become image light IML, thereby forming a display image. On the other hand, in the case of external light EXL, the external light component reflected by the reflective polarizer 11, which is the greatest cause of external light reflection, passes through the liquid crystal lens 12, and is then reflected by the reflective polarizer 11 and returns to the liquid crystal lens 12. At this time, the liquid crystal lens 12 is in a state (first state) in which it exhibits a lens effect due to the application of a voltage when passing through the liquid crystal lens 12. Therefore, the light component reflected by the light reflective polarizer 11 and returned to the liquid crystal lens 12 is refracted by the liquid crystal lens 12 as described above, refracted at an angle θ, and emitted from the liquid crystal lens 12. That is, the traveling directions of the image light IML and the external light component reflected by the reflective polarizing plate 11 are different. In other words, the separation between the image light IML and the external light component reflected by the reflective polarizing plate 11 is improved. That is, the reflection of the external light EXL in the displayed image can be reduced. In particular, when used as a rearview mirror, if the direction in which the light is refracted by the liquid crystal lens 12 and travels in an oblique direction is set so that the angle θ is in a direction different from the driver (observer of the display device 1) side, for example, in the opposite direction or upward direction, with the rearview mirror as the center, the reflected light reaching the driver can be reduced, and therefore, even if the angle θ is about 5°, the reflection of the external light EXL can be made substantially negligible.

[0021] In the above description, for ease of understanding, it has been assumed that the light components of the external light EXL that pass through the liquid crystal lens 12 and the reflective polarizer 11 and enter the display panel 10 are absorbed by the polarizer 11b without reaching the backlight 10a. However, strictly speaking, the external light components that reach the display panel 10 are also affected by the liquid crystal panel 10c within the display panel 10. Therefore, the polarization direction of some of the light is rotated 90° by the liquid crystal panel 10c, passes through the polarizer 10b, and enters the backlight 10a. At this time, some of the light components of the external light EXL that reach the backlight 10a are reflected by the backlight 10a. Because the backlight 10a is not a specular reflection surface, diffuse reflection occurs. As a result, most of the polarized light components are absorbed by the polarizer 10b. In other words, most of the components of the external light EXL that enter the backlight 10a are attenuated and not reflected outside the display device with a variable mirror 1. In other words, glare can be reduced even for external light components that pass through the reflective polarizer 11.

[0022] On the other hand, as shown in FIG. 3B, when the display unit 10 is in the non-image display state (OFF), no image light IML is generated. At this time, of the unpolarized external light EXL incident on the liquid crystal lens 12, light with the same polarization direction as the transmission axis a3 of the reflective polarizer 11 reaches the polarizer 10b as described above, but does not reach the backlight 10a and is absorbed by the polarizer 10b. Furthermore, of the light incident on the reflective polarizer 11, light with a polarization direction substantially perpendicular to the transmission axis a3 is reflected by the reflective polarizer 11 and returns to the liquid crystal lens 12. However, this light returning to the liquid crystal lens 12 passes directly through the liquid crystal lens 12, which is in a state (second state) where it does not exhibit lens action due to the application of no voltage. In other words, the reflected light of the external light EXL is reflected and travels toward the front of the display device with a variable mirror 1. Therefore, this reflected light allows the driver to see what is happening behind the vehicle.

[0023] Next, a modified example of the above-described embodiment will be described. In the display device with a variable mirror 1 of the above-described embodiment, the reflective polarizing plate 11 can be replaced with a half mirror formed with a thickness that allows transmission of a metal reflective film. Since the other configurations are the same as those of the above-described embodiment, a description thereof will be omitted here, and the modified example will be described with reference to FIG. 1, which is the same drawing as that of the above-described embodiment. The process of generating image light IML is generally the same as in the case of the display device with a variable mirror 1 of the above-described embodiment, and light emitted from the display unit 10 becomes light with a polarization direction a12. This light passes directly through the half mirror and then passes through the liquid crystal lens 12 to emit the image light IML.

[0024] On the other hand, external light EXL passes through liquid crystal lens 12, with some of its component light reflected by the half mirror, and the other component light passes through the half mirror and reaches display unit 10. The part of the component light reflected by the half mirror returns to liquid crystal lens 12. At this time, the light component polarized approximately parallel to the alignment treatment directions a4, a5 of liquid crystal lens 12 is subjected to the refraction action of liquid crystal lens 12 in the voltage applied state (ON), and is refracted and emitted from liquid crystal lens 12. In other words, it travels in an oblique direction rather than in the front direction of the display device with a variable mirror 1. Furthermore, of the part of the component light reflected by the half mirror, the light component polarized approximately perpendicular to the alignment treatment directions a4, a5 of liquid crystal lens 12 is not subjected to the refraction action of liquid crystal lens 12 in the voltage applied state (ON). In other words, it is emitted directly from liquid crystal lens 12 without being refracted. That is, of the light reflected by the half mirror, which is the greatest cause of reflections among the external light EXL, approximately 50% of the light component of that reflected light travels in an oblique direction rather than directly in front of the display device with a variable mirror 1, improving separation from the image light IML. Note that the remaining approximately 50% of the light component of the light reflected by the half mirror is not subjected to the refraction action of the liquid crystal lens 12, and therefore separation of the reflected light from the image light IML is not as good as when the above-mentioned reflective polarizing plate 11 is used. However, it is possible to reduce the reflected light to a certain extent by using a half mirror, which is less expensive than the reflective polarizing plate 11. Another advantage compared to the reflective polarizing plate 11 is that it is easier to assemble without having to consider the direction of the transmission axis when installing.

[0025] Furthermore, among the light components of the external light EXL, light that passes through the half mirror is attenuated by the half mirror. Furthermore, among the light components that reach the display unit 10, component light whose polarization direction is approximately perpendicular to the transmission axis a1 of the polarizer 10b does not reach the liquid crystal element 10c and is absorbed by the polarizer 10b. Furthermore, component light whose polarization direction is approximately the same as the transmission axis a1 of the polarizer 10b is absorbed or attenuated by the display unit 10, as is generally the case in the above-described embodiment. As a result, among the light components of the external light EXL, light that passes through the half mirror can also reduce the reflection of external light when an image is displayed.

[0026] Figures 4(A) and 4(B) are diagrams for explaining the configuration and operation of a display device with a variable mirror 1a according to another modified embodiment. To make the operation easier to understand, the cover glass 13, anti-reflection film 14, and control device 15 are omitted from Figures 4(A) and 4(B). Figure 4(A) shows the operation when the display device functions to display various images, and Figure 4(B) shows the operation when the display device functions as a mirror for the driver to check behind.

[0027] The display device with a variable mirror 1a differs from the display device with a variable mirror 1 of the embodiment shown in FIG. 1 in that the liquid crystal lens 12 is replaced with two liquid crystal lenses 12a and 12b. The liquid crystal lens 12b is disposed on the front side (light output side) of the reflective polarizing plate 11. The liquid crystal lens 12a is disposed on the front side (light output side) of the liquid crystal lens 12b. The alignment treatment directions a4 and a5 of the liquid crystal lens 12a are substantially parallel to the X direction, and the alignment treatment directions a7 and a8 of the liquid crystal lens 12b are also substantially parallel to the X direction. In other words, the alignment treatment directions a4 and a5 of the liquid crystal lens 12a and the alignment treatment directions a7 and a8 of the liquid crystal lens 12b are substantially parallel to each other.

[0028] 4(A), the process of generating image light IML is generally similar to that of the display device with a variable mirror 1 of the above-described embodiment. On the other hand, external light EXL passes through two liquid crystal lenses 12a and 12b, is reflected by reflective polarizing plate 11, enters liquid crystal lens 12b, exits liquid crystal lens 12b, and enters liquid crystal lens 12a.

[0029] Of the reflected light, the polarized light component approximately parallel to the alignment treatment directions a4 and a5 of liquid crystal lens 12a and the polarized light component approximately parallel to the alignment treatment directions a7 and a8 of liquid crystal lens 12b are refracted by liquid crystal lenses 12a and 12b in the voltage-applied state (ON), and are refracted and emitted from liquid crystal lens 12a. Because the alignment treatment directions of two liquid crystal lenses 12a and 12b are approximately parallel, the polarized light component approximately parallel to the alignment treatment directions a4, a5, a7, and a8 is refracted by each liquid crystal lens 12a and 12b and emitted. In other words, the reflected light of external light EXL can be bent more significantly in an oblique direction than in the case where a single liquid crystal lens is used, rather than in the front direction of display device 1a with a variable mirror. This improves the separation of the external light EXL from the image light IML. In other words, the glare of external light EXL on the displayed image can be reduced.

[0030] On the other hand, as shown in FIG. 4(B), when the display unit 10 is in a non-image display state (OFF), no image light IML is formed. At this time, a portion of the unpolarized external light EXL incident on the liquid crystal lens 12a passes through the liquid crystal lens 12b, is reflected by the reflective polarizer 11, and returns to the liquid crystal lens 12b. This light that returns to the liquid crystal lens 12b passes directly through the liquid crystal lenses 12a and 12b, which are in a no-voltage-applied state (OFF). In other words, the reflected light of the external light EXL is reflected and travels toward the front of the display device with a variable mirror 1. This allows the driver to see what is happening behind the vehicle.

[0031] According to each of the above-described embodiments, it is possible to reduce reflection of external light at least in the image display state of a display device with a variable mirror that is switchable between a mirror state and an image display state.

[0032] The present disclosure is not limited to the content of the above-described embodiments and can be implemented in various modifications within the scope of the gist of the present disclosure. For example, while the above-described embodiments have shown a display unit using a liquid crystal panel as an example, the configuration of the display unit is not limited to this and may be any display unit that emits linearly polarized or circularly polarized image light, such as a display unit using an organic electroluminescence element. Furthermore, while the above-described embodiments have shown an in-vehicle mirror as an example of an application of the display device with a variable mirror according to the present disclosure, the scope of application of the present disclosure is not limited thereto and may be applied to consumer products such as home appliances. [Explanation of symbols]

[0033] 1: Display device with deformable mirror, 10: Display unit, 10a: Backlight, 10b, 10d: Polarizing plates, 10c: Liquid crystal panel, 11: Reflective polarizing plate, 12: Liquid crystal lens, 13: Cover glass, 14: Anti-reflection film, 15: Control device

Claims

1. A display device with a variable mirror that can be electrically switched between a mirror state and an image display state, A display unit that emits image light; A reflective polarizing plate disposed on the light exit side of the display unit; a liquid crystal lens disposed opposite the display unit with the reflective polarizing plate interposed therebetween; a control device for controlling the operation of the display unit and the liquid crystal lens; Including, the liquid crystal lens has a pair of substrates, a liquid crystal layer disposed between the substrates, and an alignment film provided on each of the substrates, and is disposed such that a polarization direction of the image light transmitted from the display unit through the reflective polarizing plate and incident on the liquid crystal lens is substantially perpendicular to an alignment treatment direction of each of the alignment films; the liquid crystal lens is electrically switchable between a first state in which it exhibits a lens effect and a second state in which it does not exhibit the lens effect under the control of the control device; The image light incident on the liquid crystal lens in the first state exits the liquid crystal lens without changing its traveling direction. Display device with variable mirror.

2. Of the external light that passes through the liquid crystal lens in the first state and is incident on the reflective polarizing plate, the light that is reflected by the reflective polarizing plate and returns to the liquid crystal lens is refracted by the lens action of the liquid crystal lens and is emitted from the liquid crystal lens. The display device with a variable mirror according to claim 1 .

3. the display unit includes a liquid crystal panel, and a first polarizing plate and a second polarizing plate disposed opposite each other with the liquid crystal panel interposed therebetween; the first polarizing plate is disposed between the reflective polarizing plate and the liquid crystal panel; The display device with a variable mirror according to claim 1 .

4. Each of the first polarizing plate and the second polarizing plate is an absorptive linear polarizing plate. The display device with a variable mirror according to claim 3 .

5. the liquid crystal lens is a linear polarization type liquid crystal lens, a transmission axis of the reflective polarizing plate and a transmission axis of the first polarizing plate are substantially parallel to each other; the alignment treatment direction of each of the alignment films of the liquid crystal lens and the transmission axis of the reflective polarizing plate are substantially perpendicular to each other; The display device with a variable mirror according to claim 4 .

6. A display device with a variable mirror that can be electrically switched between a mirror state and an image display state, A display unit that emits image light; A half mirror disposed on the light exit side of the display unit; a liquid crystal lens disposed opposite the display unit with a reflective polarizing plate interposed therebetween; a control device for controlling the operation of the display unit and the liquid crystal lens; Including, The liquid crystal lens is electrically switchable between a first state in which the liquid crystal lens exerts a lens effect and a second state in which the liquid crystal lens does not exert the lens effect under the control of the control device. Display device with variable mirror.

Images