Display device with adjustable 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

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

Background Art

[0002] As a conventional example of a display device with a variable mirror, for example, Japanese Unexamined Patent Application Publication No. 2021-138195 (Patent Document 1) describes a vehicle interior mirror capable of switching at least between a mirror state and an image display state.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] One of the objectives of a specific aspect according to the present disclosure is to provide a technology capable of reducing the reflection of external light in the image display state of a display device with a variable mirror that can switch between a mirror state and an image display state.

Means for Solving the Problems

[0005] [1] A display device with a variable mirror according to one aspect of the present disclosure is a display device with a variable mirror capable of electrically switching between a mirror state and an image display state, a display unit that emits image light, a reflective polarizing plate disposed on the light-emitting side of the display unit, a liquid crystal lens disposed opposite to the display unit with the reflective polarizing plate interposed therebetween, a control device that controls the operations of the display unit and the liquid crystal lens, and includes The liquid crystal lens comprises a pair of substrates, a liquid crystal layer disposed between the substrates, and an alignment film provided on each of the substrates, and is arranged such that the polarization direction of the image light incident on the liquid crystal lens from the display unit through the reflective polarizer is substantially perpendicular to the alignment processing direction of each of the alignment films. The liquid crystal lens can be electrically switched between a first state in which it performs a lensing action and a second state in which it does not perform the lensing action, by the control device. The image light incident on the liquid crystal lens in the first state exits the liquid crystal lens without changing its direction of propagation. It is a display device with a variable mirror. [2] A display device with a variable mirror according to one aspect of the present disclosure is: A display device with a variable mirror that can electrically switch between a mirror state and an image display state, A display unit that emits image light, A half-mirror positioned on the light-emitting side of the display unit, The aforementioned Half mirror A liquid crystal lens is positioned opposite the display unit, with the liquid crystal lens in between. A control device that controls the operation of the display unit and the liquid crystal lens, Includes, The liquid crystal lens can be electrically switched between a first state in which it performs a lensing action and a second state in which it does not perform the lensing action, by the control device. It is a display device with a variable mirror.

[0006] According to the above configuration, it is possible to reduce the reflection of ambient light in the image display state of a display device with a variable mirror that can switch between a mirror state and an image display state. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 shows the configuration of a display device with a variable mirror according to one embodiment. [Figure 2] Figure 2 is a diagram illustrating the operating principle of a liquid crystal lens. [Figure 3]Figures 3(A) and 3(B) illustrate the operation of a display device with a variable mirror. [Figure 4] Figures 4(A) and 4(B) illustrate the configuration and operation of a variable mirror display device in a modified embodiment. [Modes for carrying out the invention]

[0008] Figure 1 shows the configuration of a variable mirror display device according to one embodiment. The illustrated variable mirror display device 1 comprises a display unit 10, a reflective polarizing plate 11, a liquid crystal lens 12, a cover glass 13, and an anti-reflective film 14. The display unit 10 comprises a backlight 10a, a pair of polarizing plates 10b and 10d, and a liquid crystal panel 10c. In Figure 1, each component is shown separately for clarity, but in reality, each component is arranged in close contact with each other without any gaps. This variable mirror display device 1 is used, for example, as a rearview mirror mounted in the cabin of a vehicle, and allows the driver to arbitrarily switch between functions of displaying various images and functioning as a mirror for checking behind the vehicle.

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

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

[0011] The reflective polarizer 11 is positioned on the front side (light emission side) of the display unit 10. This reflective polarizer 11 may have, for example, a wire grid made of numerous fine metal wires, or an optical multilayer film. In this embodiment, the transmission axis a3 of the reflective polarizer 11 is substantially parallel to the Y direction. Although the reflective polarizer 11 can also perform the function of the polarizer 10d and the polarizer 10d can be omitted, the polarization degree of the transmitted light can be further improved by using the reflective polarizer 11 and the polarizer 10d together.

[0012] The liquid crystal lens 12 is an element that can switch between a light-transmitting state and a lens state by voltage. Various known liquid crystal lenses can be used as such a liquid crystal lens 12, for example, those described in public documents such as Japanese Patent Application Publication No. 2014-112157 and Japanese Patent Application Publication No. 2018-101026 can be used.

[0013] The cover glass 13 is a glass plate placed on the front side (light-emitting side) of the liquid crystal lens 12 to protect the display unit 10 and the liquid crystal lens 12. The anti-reflective film 14 is placed on the front side (light-emitting side) of the cover glass 13 and suppresses the reflection of external light from the cover glass 13. The control device 15 controls the operation 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 electrodes 101a and 101b, and liquid crystal layer 103 is provided between each of electrodes 101a and 101b and common electrode 102. Each of electrodes 101a and 101b is configured such that a voltage can be individually applied from the outside.

[0015] In the liquid crystal lens 12 of the illustrated example, 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 illustrated example, 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 action of the lens can be obtained in the portion where this refractive index distribution is generated. In the illustrated example, 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 is also reversed. When no voltage is applied between each of electrodes 101a and 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 depending on whether a voltage is applied or not. Also, if the positions where each of electrodes 101a and 101b for forming the refractive index distribution are provided are changed, the direction of refraction can also be adjusted. If more electrodes are formed, various refractive index distributions can be generated.

[0016] Substrates 90 and 91 are each provided with an alignment film (not shown). The alignment processing direction (e.g., rubbing processing direction) a4 on substrate 90 is, for example, rightward in the figure, and the alignment processing direction (e.g., rubbing processing direction) a5 on substrate 91 is, for example, leftward in the figure. These alignment processing directions a4 and a5 are arranged substantially parallel to the X direction respectively in the coordinates shown in FIG. 1. Also, the alignment processing directions a4 and a5 are anti-parallel to each other. Thereby, the polarization in the direction substantially parallel to these alignment processing directions a4 and a5 undergoes the above-described refraction effect and the traveling direction changes. On the other hand, the polarization in the direction substantially orthogonal to the alignment processing directions a4 and a5 does not undergo the refraction effect, and thus the traveling direction does not change. Here, the alignment processing directions a4 and a5 of the liquid crystal lens 12 can also be appropriately changed depending on the device, application, etc. to which the display device 1 with a variable mirror is applied.

[0017] FIG. 3(A) and FIG. 3(B) are diagrams for explaining the operation of the display device 1 with a variable mirror. In FIGS. 3(A) and 3(B), for clarity of the operation, the illustration of the cover glass 13, the antireflection film 14, and the control device 15 is omitted. FIG. 3(A) shows the operation when exhibiting the function of performing various image displays, and FIG. 3(B) shows the operation when exhibiting the function as a mirror for the driver to check the rear.

[0018] As shown in Figure 3(A), the unpolarized light emitted from the backlight 10a and incident on the polarizer 10b has a light component with the same polarization direction a11 as the transmission axis a1, and is incident on the liquid crystal panel 10c. In this embodiment, the light incident on the liquid crystal panel 10c has its polarization direction rotated by 90° by the liquid crystal panel 10c, which is in the image display state (ON), and is incident on the polarizer 10d. Since the polarization direction a12 of this light is approximately parallel to the transmission axis a2 of the polarizer 10d, it passes through the polarizer 10d and is incident on the reflective polarizer 11. Since the transmission axis a3 of the reflective polarizer 11 is approximately parallel to the polarization direction a12, this light is emitted directly from the reflective polarizer 11. This light with polarization direction a13 is incident on the liquid crystal lens 12. Since the polarization direction a13 of this light is approximately perpendicular to the orientation processing directions a4 and a5 of the liquid crystal lens 12, it is emitted without changing its direction of propagation. The polarization direction a14 of the image light IML emitted from the liquid crystal lens 12 is approximately parallel to the Y direction in the figure. The displayed image is formed by this image light IML.

[0019] Unpolarized ambient light EXL incident on the liquid crystal lens 12 from the outside passes through the liquid crystal lens 12 and enters the reflective polarizer 11. Light with the same polarization direction as the transmission axis a3 passes through the reflective polarizer 11, and further passes through the polarizer 10d and the liquid crystal panel 11c. The light that has passed through the liquid crystal panel 10c has a polarization direction that is approximately perpendicular to the transmission axis a1 of the polarizer 10b, so it is absorbed by the polarizer 10b without reaching the backlight 10a. In addition, of the light incident on the reflective polarizer 11, the light with a polarization direction that is approximately perpendicular to the transmission axis a3 is reflected by the reflective polarizer 11 and returns to the liquid crystal lens 12. The light that returns to the liquid crystal lens 12 has a polarization direction that is approximately parallel to the orientation processing directions a4 and a5 of the liquid crystal lens 12, so it is refracted by the liquid crystal lens 12, which is in a state where it exhibits a lens effect (first state) when a voltage is applied, and is refracted at an angle θ and exits from the liquid crystal lens 12. This angle θ depends on the configuration of the liquid crystal lens 12, but for example, an angle of 10° or more can be obtained. In other words, the reflected light from the ambient light EXL travels diagonally rather than in the direction directly in front of the display device 1 with the variable mirror.

[0020] In this embodiment, as described above, when planar light emitted from the backlight 10a is incident on the liquid crystal panel 10c, this light is appropriately modulated in the liquid crystal panel 10c and passes through the polarizing plate 10d, thereby forming image light by the display unit 10. This image light passes directly through the reflective polarizing plate 11 and then directly through the liquid crystal lens 12, becoming image light IML, and thereby forming a displayed image. On the other hand, in the case of ambient light EXL, the ambient light component reflected by the reflective polarizing plate 11, which is the cause of ambient light reflection in ambient light EXL, passes through the liquid crystal lens 12, is reflected by the reflective polarizing plate 11 and returns to the liquid crystal lens 12. At this time, the liquid crystal lens 12 is in a state (first state) where it exhibits a lensing effect due to the voltage applied when light passes through the liquid crystal lens 12, so the light component reflected by the light-reflecting polarizing plate 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 exits from the liquid crystal lens 12. In other words, the direction of propagation of the image light IML and the ambient light component reflected by the reflective polarizer 11 will be different. To put it another way, the separation between the image light IML and the ambient light component reflected by the reflective polarizer 11 will be improved. This means that reflections of ambient light EXL on the displayed image can be reduced. In particular, when used as a rearview mirror, if the direction of propagation of light refracted by the liquid crystal lens 12 at an angle θ is set to be different from the direction of the driver (observer of the display device 1) with respect to the rearview mirror, for example, in the opposite direction or upward, the reflected light reaching the driver can be reduced, so that reflections of ambient light EXL can be practically ignored even if the angle θ is about 5°.

[0021] In the above explanation, for the sake of ease of understanding, it was stated that the light component that passes through the liquid crystal lens 12 and the reflective polarizer 11 in the ambient light EXL and enters the display panel 10 is absorbed by the polarizer 11b without reaching the backlight 10a. However, strictly speaking, the ambient light component that reaches the display panel 10 in the ambient light EXL is also affected by the liquid crystal panel 10c within the display panel 10. Therefore, some of the light has its polarization direction rotated by 90° by the liquid crystal panel 10c, passes through the polarizer 10b, and enters the backlight 10a. At this time, some of the light component in the ambient light EXL that reaches the backlight 10a is reflected by the backlight 10a. Since the backlight 10a is not a specular reflecting surface, diffuse reflection occurs. As a result, most of the polarization component is absorbed by the polarizer 10b. In other words, most of the component of the ambient light EXL that enters the backlight 10a is attenuated and not reflected outside the display device 1 with variable mirror. In other words, reflections of ambient light components that pass through the reflective polarizer 11 can also be reduced.

[0022] On the other hand, as shown in Figure 3(B), when the display unit 10 is in a non-image display state (OFF), no image light IML is formed. In this case, of the unpolarized ambient 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 is absorbed by the polarizer 10b without reaching the backlight 10a. Also, of the light incident on the reflective polarizer 11, light with a polarization direction approximately perpendicular to the transmission axis a3 is reflected by the reflective polarizer 11 and returns to the liquid crystal lens 12. This light that returns to the liquid crystal lens 12 passes directly through the liquid crystal lens 12, which is in a state where it does not perform a lensing action (second state) due to the absence of applied voltage. In other words, the reflected light from ambient light EXL is reflected and propagates in the direction of the front of the variable mirror display device 1. Therefore, this reflected light allows the driver to see what is behind them.

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

[0024] On the other hand, with respect to ambient light (EXL), some of the light components pass through the liquid crystal lens 12, are reflected by the half mirror, and other components pass through the half mirror to reach the display unit 10. The light components reflected by the half mirror return to the liquid crystal lens 12. At this time, the light components with polarizations approximately parallel to the orientation processing directions a4 and a5 of the liquid crystal lens 12 are refracted by the liquid crystal lens 12 when the voltage is applied (ON), and are refracted and emitted from the liquid crystal lens 12. That is, they travel in an oblique direction rather than in the front direction of the variable mirror display device 1. Furthermore, of the light components with polarizations approximately perpendicular to the orientation processing directions a4 and a5 of the liquid crystal lens 12 among the light components reflected by the half mirror are not refracted by the liquid crystal lens 12 when the voltage is applied (ON). That is, they are emitted from the liquid crystal lens 12 as is without being refracted. In other words, the reflected light from the half-mirror, which is the main cause of reflections in the ambient light EXL, travels diagonally rather than in the front direction of the variable mirror display device 1 for approximately 50% of its light component, thus improving the separation from the image light IML. However, since the remaining approximately 50% of the light component of the reflected light from the half-mirror is not affected by the refractive effect of the liquid crystal lens 12, the separation of the reflected light from the image light IML is not as good as when using the reflective polarizer 11 described above. Nevertheless, it is possible to reduce reflected light to some extent by using a half-mirror, which is less expensive than the reflective polarizer 11. It also has the advantage of being easier to assemble compared to the reflective polarizer 11, as there is no need to consider the direction of the transmission axis when installing it.

[0025] Furthermore, among the light components of the ambient light EXL, the light that passes through the half mirror is attenuated by the half mirror. In addition, among the light components that reach the display unit 10, the component light whose polarization direction is approximately perpendicular to the transmission axis a1 of the polarizer plate 10b is absorbed by the polarizer plate 10b without reaching the liquid crystal element 10c. Also, the component light whose polarization direction is approximately equal to the transmission axis a1 of the polarizer plate 10b is generally the same as in the embodiment described above, and is absorbed or attenuated by the display unit 10. As a result, even among the light components of the ambient light EXL, the reflection of ambient light in the image display state can be reduced even for the light components that pass through the half mirror.

[0026] Figures 4(A) and 4(B) illustrate the configuration and operation of the variable mirror-equipped display device 1a in other modified embodiments. In Figures 4(A) and 4(B), the cover glass 13, anti-reflective coating 14, and control device 15 are omitted from the illustration for clarity of the operation. Figure 4(A) shows the operation when the device performs its function of displaying various images, and Figure 4(B) shows the operation when it functions as a mirror for the driver to check behind them.

[0027] The variable mirror display device 1a differs from the variable mirror display device 1 of the embodiment shown in Figure 1 above in that the liquid crystal lens 12 is replaced by two liquid crystal lenses 12a and 12b. The liquid crystal lens 12b is located on the front side (light emission side) of the reflective polarizing plate 11. The liquid crystal lens 12a is located on the front side (light emission side) of the liquid crystal lens 12b. The orientation processing directions a4 and a5 of the liquid crystal lens 12a are approximately parallel to the X direction, and the orientation processing directions a7 and a8 of the liquid crystal lens 12b are also approximately parallel to the X direction. In other words, the orientation processing directions a4 and a5 of the liquid crystal lens 12a and the orientation processing directions a7 and a8 of the liquid crystal lens 12b are approximately parallel.

[0028] As shown in Figure 4(A), the process of generating image light IML is generally the same as in the case of the variable mirror display device 1 of the embodiment described above. On the other hand, for ambient light EXL, it passes through the two liquid crystal lenses 12a and 12b, is reflected by the reflective polarizer 11 and incident on the liquid crystal lens 12b, exits the liquid crystal lens 12b and incident on the liquid crystal lens 12a.

[0029] Of the reflected light, the light with polarization components approximately parallel to the orientation processing directions a4 and a5 of the liquid crystal lens 12a and the light with polarization components approximately parallel to the orientation processing directions a7 and a8 of the liquid crystal lens 12b are refracted by the respective liquid crystal lenses 12a and 12b when the voltage is applied (ON), and are refracted and emitted from the liquid crystal lens 12a. Since the orientation processing directions of the two liquid crystal lenses 12a and 12b are approximately parallel, the light with polarization components approximately parallel to the orientation processing directions a4, a5, a7, and a8 is refracted by the respective liquid crystal lenses 12a and 12b and emitted. In other words, the reflected light from ambient light EXL can be bent more significantly in an oblique direction than when a single liquid crystal lens is used, rather than in the direction of the front of the display device 1a with a variable mirror. Therefore, the separation from the image light IML is improved. In other words, reflections of ambient light EXL on the displayed image can be reduced.

[0030] On the other hand, as shown in Figure 4(B), when the display unit 10 is in a non-image display state (OFF), no image light IML is formed. At this time, some components of the unpolarized ambient light EXL incident on the liquid crystal lens 12a pass through the liquid crystal lens 12b, are reflected by the reflective polarizer 11, and return to the liquid crystal lens 12b. This light that returns to the liquid crystal lens 12b passes directly through each liquid crystal lens 12a and 12b, which are in a voltage-free state (OFF). In other words, the reflected light from the ambient light EXL is reflected and propagates in the direction of the front of the variable mirror display device 1. Therefore, the driver can see what is happening behind them.

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

[0032] It should be noted that this disclosure is not limited to the contents of the embodiments described above, and can be implemented in various modified forms within the scope of the gist of this disclosure. For example, although the embodiments described above showed a liquid crystal panel as an example of a display unit, the configuration of the display unit is not limited thereto, and any display unit that emits linearly polarized or circularly polarized image light is acceptable, and may, for example, be a display unit using an organic electroluminescent element. Also, although the embodiments described above cited an in-vehicle mirror as an example of an application of the variable mirror display device according to this disclosure, the scope of application of this disclosure is not limited thereto, and may be applied to consumer goods such as housing equipment, for example. [Explanation of Symbols]

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

Claims

1. A display device with a variable mirror that can electrically switch between a mirror state and an image display state, A display unit that emits image light, A reflective polarizing plate is positioned on the light-emitting side of the display unit, A liquid crystal lens is positioned opposite the display unit with the reflective polarizing plate in between, A control device that controls the operation of the display unit and the liquid crystal lens, Includes, The liquid crystal lens comprises a pair of substrates, a liquid crystal layer disposed between the substrates, and an alignment film provided on each of the substrates, and is arranged such that the polarization direction of the image light incident on the liquid crystal lens from the display unit through the reflective polarizer is substantially perpendicular to the alignment processing direction of each of the alignment films. The liquid crystal lens can be electrically switched between a first state in which it performs a lensing action and a second state in which it does not perform the lensing action, by the control device. The image light incident on the liquid crystal lens in the first state exits the liquid crystal lens without changing its direction of propagation. Display device with adjustable mirror.

2. Of the ambient light that passes through the liquid crystal lens in the first state and is incident on the reflective polarizer, the light that is reflected by the reflective polarizer and returns to the liquid crystal lens is refracted by the lens action of the liquid crystal lens and exits from the liquid crystal lens. 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 arranged opposite each other with the liquid crystal panel in between. The first polarizing plate is placed between the reflective polarizing plate and the liquid crystal panel. Display device with a variable mirror according to claim 1 or 2.

4. Each of the first polarizer and the second polarizer is an absorption-type linear polarizer. Display device with a variable mirror according to claim 3.

5. The aforementioned liquid crystal lens is a linearly polarized liquid crystal lens, The transmission axis of the reflective polarizer and the transmission axis of the first polarizer are substantially parallel. The orientation processing direction of each of the alignment films in the liquid crystal lens and the transmission axis of the reflective polarizer are substantially intersecting. Display device with a variable mirror according to claim 4.

6. A display device with a variable mirror that can electrically switch between a mirror state and an image display state, A display unit that emits image light, A half-mirror positioned on the light-emitting side of the display unit, A liquid crystal lens is positioned opposite the display unit with the half-mirror in between, A control device that controls the operation of the display unit and the liquid crystal lens, Includes, The liquid crystal lens can be electrically switched between a first state in which it performs a lensing action and a second state in which it does not perform a lensing action, by the control device. Display device with adjustable mirror.

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