Method for reducing disclination in a 2D / 3D switchable autostereoscopic display device

Abstract

The present invention relates to a method for reducing disclination in an autostereoscopic display device that is electrically switchable between a 2D view mode and a 3D view mode. The method includes changing the angle between two liquid crystal alignment directions in a lenticular device, thereby determining an angle that results in a minimal or acceptable occurrence of disclination after switching between both view modes. The present invention further relates to an autostereoscopic display device that exhibits reduced disclination when switching between both view modes.

Description

Technical Field

[0001] The present invention relates to a method for reducing disclination in an autostereoscopic display device that can be electrically switched from a first view mode to a second view mode, and an autostereoscopic display device that can be electrically switched from a first view mode to a second view mode.

Background Art

[0002] Display devices that can be electrically switched between a two-dimensional view mode and a three-dimensional view mode, generally known as 2D / 3D switchable autostereoscopic display devices, have received significant attention over the past 20 years. A common approach is to arrange an array of pixels together with a lenticular device comprising an array of semi-cylindrical microlenses (lenticulars) adjacent to a liquid crystal medium that can be switched between two liquid crystal alignments under the influence of an electric field. In the first alignment, the director of the liquid crystal medium is in the plane of the display device, and in the second alignment, the director of the liquid crystal medium is perpendicular to the plane of the display device.

[0003] In such a configuration, each lenticular is associated with a group of at least two columns of (sub) pixels that extend parallel to or at an angle (tilted) with respect to the lens. The pixel output that travels through the lenticular device follows the optical properties of the lenticular and the liquid crystal medium. The refractive index of the lenticular is fixed, while the refractive index of the adjacent liquid crystal medium can be switched between two values by switching between two liquid crystal alignments. The first refractive index corresponds to light polarized along the director of the liquid crystal, and the second refractive index corresponds to light polarized perpendicular to the director. When the pixel output travels substantially perpendicular to the plane of the display device, the pixel output "sees" either the first or the second refractive index. In the first viewing mode, the liquid crystal medium is in the first alignment. Its refractive index matches that of the lenticular, thereby robbing the lenticular of its focusing effect and causing the lenticular device to behave as a transparent and flat optical panel. This forms the two-dimensional viewing mode of the autostereoscopic display device. In the second viewing mode, the liquid crystal medium is in the second liquid crystal alignment. Since the refractive indices do not match, each lenticular can exhibit a focusing effect. This makes it possible to direct the outputs from different pixel columns to different spatial positions in front of the display device, which in turn makes it possible for the viewer to perceive a three-dimensional image composed of a left image and a right image. This forms the three-dimensional viewing mode of the autostereoscopic display device. Thus, it will be apparent that well-controlled switching between liquid crystal alignments is important in the design of a display device that can switch between a two-dimensional viewing mode and a three-dimensional viewing mode.

[0004] The switching from one liquid crystal alignment to another is caused by changing the electric field that the liquid crystal material experiences. This usually involves either applying an electric field (when such an electric field does not exist) or switching off an electric field (when exposed to such an electric field). It is important that the liquid crystal alignment changes uniformly due to such a change in the electric field. However, this is often not the case. It is then observed that different domains with different liquid crystal alignments are formed in the liquid crystal medium. At the boundaries of these domains, the orientation of the liquid crystal molecules changes abruptly. Such boundaries are called "disclinations". The optical properties of adjacent domains are not exactly the same, and optical aberrations occur at the disclinations. This leads to an increase in crosstalk when switched to the 3D viewing mode and a decrease in image quality when switched to the 2D viewing mode.

[0005] In conventional electrically switchable 2D / 3D display devices, disclinations are a problem. They are formed when switching from one liquid crystal alignment to another. Furthermore, this is usually not limited to a single occurrence in a particular display device. Disclinations often appear at multiple positions on the display device. In addition to their formation, their persistence is a problem, as many disclinations are stable for longer periods, for example, exceeding 1 minute, exceeding 10 minutes, or even permanently.

[0006] To date, several efforts have been made to reduce or even completely prevent the formation of disclinations. For example, attempts have been made to apply an electric field with a specific profile by applying a voltage with a specific ramp (see, for example, WO 2020135731). This reduces the problem to some extent, but its implementation is insufficient.

[0007] A specific drawback is that when using a voltage lamp, 2D / 3D switching takes more time. During that time, typically 5 to 30 seconds, the performance of the display device is impaired, specifically, the level of crosstalk increases. Also, specific voltage lamps have to be carefully programmed and tested for each new model type, while manufacturing variations can easily cause inconsistencies between the behavior of the liquid crystal medium and the voltage lamp. SUMMARY OF THE INVENTION

[0008] Accordingly, an object of the present invention is to provide an electrically switchable 2D / 3D display device in which disclinations are not formed or are formed to a lesser extent during switching than in at least known switching processes. For example, the size, number and / or duration of the disclinations are reduced. It is also an object that the disclinations only exist for a time span that is too short to be recognized as a problem. It is also an object to provide a solution that is not more complex than solutions known in the art. More generally, an object of the present invention is to improve the viewing experience of the viewer of an autostereoscopic display device.

[0009] It has been found that one or more of these objects can be achieved by adapting the polarization direction of the display output.

[0010] Accordingly, the present invention relates to a method for reducing disclinations in an autostereoscopic display device (11) that is electrically switchable between a first view mode and a second view mode, the autostereoscopic display device (11) comprising - a display panel (1), ○ an array of display pixel elements for generating a display output, ○ a linear polarizer configured to filter the display output in a clearly defined polarization direction, the display panel (1) comprising - A lenticular device (2) provided on top of a display panel (1) and electrically switchable to provide a first view mode or a second view mode, the lenticular device (2) comprising: ○ A first optically transparent substrate (4) comprising an array of lenticular elements having a first inner surface (4a) with liquid crystal alignment characteristics having a first liquid crystal alignment direction; ○ A second optically transparent substrate (5), - An outer surface (5b) configured to receive a display output facing a linear polarizer; - A second inner surface (5a) having liquid crystal alignment characteristics having a second liquid crystal alignment direction that coincides with the polarization direction of the linear polarizer, the first inner surface (4a) and the second inner surface (5a) facing each other, the second optically transparent substrate (5) having; ○ A first planar switching electrode (6) disposed on the side of the first optically transparent substrate (4); ○ A second planar switching electrode (7) disposed on the side of the second optically transparent substrate (5); ○ A liquid crystal medium (8) containing liquid crystal molecules (9), the liquid crystal medium (8) being sandwiched between two substrates (4, 5) and in contact with the first inner surface (4a) and the second inner surface (5a); - In the first view mode, the liquid crystal molecules (9) are in the plane of the two planar switching electrodes (6, 7) and - In the second view mode, the liquid crystal molecules (9) are oriented perpendicular to the two planar switching electrodes (6, 7), the lenticular device (2); - Means (3) for applying a switching voltage to both ends of both planar switching electrodes (6, 7) to achieve switching from the first view mode to the second view mode; In the first view mode, the liquid crystal molecules (9) define a helix (10) having a helical twist defined by the angle between the first liquid crystal alignment direction and the second liquid crystal alignment direction; The method includes changing the angle between a first liquid crystal alignment direction and a second liquid crystal alignment direction in a lenticular device (2), thereby determining an angle that results in a minimal or acceptable occurrence of disclination after switching from a first view mode to a second view mode.

[0011] The present invention further relates to an autostereoscopic display device (11) that is electrically switchable between a first view mode and a second view mode. The autostereoscopic display device (11) comprises: - A display panel (1), ○ An array of display pixel elements for generating a display output, ○ A linear polarizer configured to filter the display output in a clearly defined polarization direction, and a display panel (1) comprising the same; - A lenticular device (2) provided on the display panel and electrically switchable to provide a first view mode or a second view mode. The lenticular device (2) comprises: ○ A first optically transparent substrate (4) comprising an array of lenticular elements having a first inner surface (4a) with liquid crystal alignment characteristics having a first liquid crystal alignment direction, ○ A second optically transparent substrate (5), - An outer surface (5b) configured to receive the display output facing the linear polarizer, - A second inner surface (5a) having liquid crystal alignment characteristics having a second liquid crystal alignment direction that coincides with the polarization direction of the linear polarizer, and the first inner surface (4a) and the second inner surface (5a) face each other. A second optically transparent substrate (5) having a second inner surface (5a); ○ A first planar switching electrode (6) disposed on the side of the first optically transparent substrate (4), ○ A second planar switching electrode (7) disposed on the side of the second optically transparent substrate (5), ○A liquid crystal medium (8) containing liquid crystal molecules (9), and the liquid crystal medium (8) is sandwiched between two substrates (4, 5) and is in contact with the first inner surface (4a) and the second inner surface (5a). - In the first viewing mode, the liquid crystal molecules (9) are in the plane of the two planar switching electrodes (6, 7), and - In the second viewing mode, the liquid crystal molecules (9) are oriented perpendicular to the two planar switching electrodes (6, 7), a lenticular device (2), - Means (3) for applying a switching voltage to both ends of both planar switching electrodes (6, 7) to achieve switching from the first viewing mode to the second viewing mode. - In the first viewing mode, the liquid crystal molecules (9) define a helix (10) having a helical twist defined by the angle between the first liquid crystal alignment direction and the second liquid crystal alignment direction. - The angle between the first liquid crystal alignment direction and the second liquid crystal alignment direction is in the range of 4 to 86°).

[0012] The angle is specifically the angle that results in a minimum or acceptable occurrence of disclination after the autostereoscopic display device (11) is switched from the first viewing mode to the second viewing mode.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

DETAILED DESCRIPTION OF THE INVENTION

[0014] The elements in the figures are shown for simplicity and clarity and are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve the understanding of various exemplary embodiments of the present invention. For example, the relative dimensions of schematic liquid crystal molecules and lenticular elements with respect to other components of an autostereoscopic display device cannot be derived from the figures. Also, the angles that can be derived from the figures do not necessarily have the same values as the exemplary values reported in the descriptions of these angles.

[0015] Furthermore, terms such as "first", "second", etc. in this specification and the claims are generally used, if at all, to distinguish similar elements and are not necessarily used to describe a sequential or time-based order.

[0016] In the context of the present invention, the term "viewer" means a person who consumes, specifically can view, the content presented by an autostereoscopic display device. Throughout the text, references to the viewer are made by male words such as "he", "him", or "his". This is for purposes of clarity and brevity only, and it is understood that female words such as "she" and "her" are equally applicable.

[0017] In the context of the present invention, the term "twist" or "helical twist" means the absolute and total angle by which the helix is twisted, determined from the start to the end of the helix. In known lenticular devices, the twist of the helix formed by liquid crystal molecules is usually from 0 to 180°, specifically from 0 to 90°. In the lenticular device (2) according to the present invention, the twist is within the range of 4 to 86°. Since the helix exists between the first inner surface (4a) and the second first inner surface (5a), the start and end points of the helix are marked by these two surfaces.

[0018] It is understood that the liquid crystal medium is a birefringent material and has a first refractive index for light traveling along the director of the liquid crystal medium and a second refractive index for light traveling perpendicular to the director of the liquid crystal medium. When the term "refractive index" is used throughout the text in relation to the liquid crystal medium, unless otherwise specified, this refers to the refractive index of the liquid crystal medium in the direction perpendicular to the plane switching electrodes, i.e., the direction in which the display output travels. This refractive index can refer to the first refractive index or the second refractive index defined above, depending on the electric field applied across the liquid crystal medium.

[0019] The autostereoscopic display device (11) used in the method of the present invention comprises three main elements (1, 2, 3). These elements are also shown in FIGS. 1 and 2. - A display panel (1) for the purpose of providing a linearly polarized display output (i.e., light), - A lenticular device (2) provided on the display panel (1) and capable of switching the optical properties for directing the linearly polarized pixel output to the viewer as a single image (two-dimensional view) or as a left image and a right image (three-dimensional view or autostereoscopic view), - Means (3) for applying a switching voltage to both ends of the two plane switching electrodes (6, 7) to enable switching between these two optical properties.

[0020] In the lenticular device 2, the liquid crystal medium (8) is present between two opposing surfaces, i.e., in contact with both surfaces. These are the first inner surface (4a) which is the lenticular surface of an array of lenticular elements (this array being part of a first optically transparent substrate), and the second inner surface (4b) which is the flat surface of a second optically transparent substrate. Both inner surfaces (4a, 4b) have liquid crystal alignment characteristics. The liquid crystal alignment characteristics of the first inner surface (4a) have a first liquid crystal alignment direction, and the liquid crystal alignment characteristics of the second inner surface (4b) have a second liquid crystal alignment direction. The display output enters the liquid crystal medium (8) via the interface with the second inner surface (4b) and exits the liquid crystal medium (8) via the interface with the first inner surface (4a). Next, the display output travels through the lenticular elements.

[0021] Preferably, the first liquid crystal alignment direction (on the lenticular surface) is usually parallel to the longitudinal direction of the lenticular element. This is because the introduction of the liquid crystal alignment direction is performed by rubbing the surface in the direction in which the alignment is desired. When it is necessary to rub the surface of the lenticular element, it is more advantageous to rub in the lenticular direction rather than at an angle to the lenticular direction.

[0022] The first optically transparent substrate (4) has an outer surface facing the viewer of the autostereoscopic display device (11), and the second optically transparent substrate (5) has an outer surface facing the display element (1).

[0023] The liquid crystal medium (8) contains liquid crystal molecules (9). Since the two planar switching electrodes (6, 7) are positioned on both sides of the liquid crystal medium (8), an electric field can be applied across the liquid crystal medium (8). The liquid crystal molecules (9) can be oriented within the plane of the planar switching electrodes (6, 7) under the influence of the alignment characteristics of both surfaces, or perpendicular to the plane of the planar switching electrodes (6, 7) under the influence of the voltage applied across both switching electrodes (6, 7). When the voltage is sufficiently reduced, preferably completely removed, the liquid crystal molecules can return to the orientation within the plane of the planar switching electrodes and follow the alignment characteristics of both surfaces.

[0024] The planar alignment and the normal alignment are shown in FIGS. 1 and 2 respectively, which are cross-sectional views of a known auto-stereoscopic display device (11). The liquid crystal molecules (9) in FIG. 1 have an elongated direction in a plane parallel to the plane of the planar switching electrodes (first viewing mode). Means (3) does not apply a voltage. The liquid crystal molecules (9) have a direction that varies within their plane, which appears as their existence in the form of a helix (10), as will be further explained below. The liquid crystal molecules (9) in FIG. 2 have an elongated direction perpendicular to the plane of the planar switching electrodes (second viewing mode). Means (3) applies an alternating switching voltage.

[0025] In the absence of a potential, the molecules align in the plane of the planar switching electrodes according to the liquid crystal alignment characteristics of the first and second surfaces, defining the first viewing mode. When a sufficiently strong potential (“switching voltage”) is applied, they switch to an alignment along the corresponding electric field perpendicular to the plane of the planar switching electrodes, defining the second viewing mode. Thus, the switching voltage is the voltage at which the auto-stereoscopic display device changes to and remains in the second viewing mode. Usually, there is a threshold voltage, and above it, a change to the second viewing mode occurs. Thus, the switching voltage is, in principle, any voltage above this threshold voltage.

[0026] The auto-stereoscopic display device may be configured such that the first viewing mode corresponds to optical characteristics that provide a two-dimensional view and the second viewing mode corresponds to optical characteristics that provide a three-dimensional view. Alternatively, it may be configured such that the first viewing mode corresponds to optical characteristics that provide a three-dimensional view and the second viewing mode corresponds to optical characteristics that provide a two-dimensional view.

[0027] In the view mode in which a three-dimensional view is provided, the lenticular device (2) has optical characteristics that enable it to direct display outputs from different display pixel elements to different spatial positions within the field of view of the autostereoscopic display device (11) in order to enable the display of a stereoscopic image composed of a left image and a right image.

[0028] As described above, the liquid crystal medium is sandwiched between two surfaces each having liquid crystal alignment characteristics, namely, the first and second inner surfaces. The display output of the display panel first intersects the second inner surface and then intersects the first inner surface. The liquid crystal alignment (i.e., the second liquid crystal alignment direction) of the second inner surface must be aligned with the polarization direction of the linear polarizer. As a result, the display output entering the liquid crystal medium is linearly polarized in the (average) direction of the long molecular axis of the liquid crystal molecules (i.e., the director). In this way, the display output "sees" the intended refractive index of the liquid crystal medium.

[0029] However, there is an exception to the above description that the polarization direction of the linear polarizer is the same as the second liquid crystal alignment direction. This is the case where a so-called "polarization rotator" is positioned between the linear polarizer and the second inner surface, which is a means capable of rotating the polarization direction of the light passing through it. Next, the polarization rotator rotates the polarization direction of the light emitted from the linear polarizer to the second liquid crystal alignment direction. Such a polarization rotator may be provided as a foil or an optical plate, and the rotation characteristics are included in the material of the foil or the optical plate. Alternatively, it may be provided in the form of a liquid crystal cell that operates through the same principle of the helical liquid crystal alignment as the lenticular device of the present invention (except, of course, that the lenticular element is missing).

[0030] However, an angular match with the polarization direction of the display output is not necessary with respect to the first inner surface from which the display output exits the liquid crystal medium. The first inner surface may have alignment characteristics in a direction different from the alignment characteristics of the second inner surface. As a result, the liquid crystal molecules stacked between the two surfaces gradually follow this direction change by forming a helix. This is shown, for example, in FIG. 1, which shows an autostereoscopic display device (11) comprising a lenticular device (2), where the helix is seen from the side, the helix axis is parallel to the plane in which the figure is shown and perpendicular to the plane of the plane-switching electrodes (the seemingly short molecules (9) are not in the plane in which the figure is shown and the seemingly longest molecules (9) are in the plane in which the figure is shown). Then, the helical twist α of the helix t is defined as the angle between the two liquid crystal alignment directions (the angle between two end molecules at each end of the helix). This is shown in FIG. 3, where the helix axis is perpendicular to the plane in which the figure is shown (FIG. 3 will be further explained below).

[0031] As long as the angle between two adjacent liquid crystal molecules within the helix does not exceed a specific (quantum mechanically defined) angle, the polarization of the display output follows the direction of the long molecular axis of the liquid crystal molecules along the helix towards the first inner surface. In this way, as the display output travels through the liquid crystal medium, the polarization direction of the display output effectively changes. The angle between the two alignment directions does not affect the optical properties of the lenticular device (at least not the properties relevant to the proper operation of the autostereoscopic display device). When this requirement is met, the angle between the two alignment directions can, in principle, be any angle between 0° and 180°.

[0032] FIG. 3 shows a simplified representation of the lenticular device (2) of FIG. 1, showing only the first optically transparent substrate (4) and the second optically transparent substrate (5), which are parallel to the plane in which the figure is presented. For clarity, the array of lenticular elements is not shown in FIG. 3. The second optically transparent substrate (5) is shown at the front and is at an angle α with respect to the vertical pIt has a horizontal liquid crystal alignment and a horizontal display polarization. The first optically transparent substrate 4 is shown in the background and is at an angle α with respect to the vertical s and has a liquid crystal alignment in the tilt direction. The overall twist α of the helix t is shown by 10 steps that gradually thin towards the background plate. This representation evokes the steps of a spiral staircase seen from above.

[0033] However, the inventors have found that a specific angle between the two alignment directions results in more disclinations during the switching from the first view mode to the second view mode, i.e., when the liquid crystal molecules switch from an alignment in the plane of the switching electrodes (having a specific helical stack) to an alignment perpendicular to the two planar switching electrodes, than other angles. It seemed possible to reach an optimal angle between the two alignment directions so as to minimize or even completely eliminate the problems related to disclinations. Specifically, it seemed that one or more of a reduction in their size, a reduction in their number (e.g., per switching event for each autostereoscopic display device), and a reduction in their duration occurred.

[0034] The switching in the reverse direction, i.e., from the second view mode to the first view mode, generally seems not to generate disturbing disclinations (however the actual twist α of the helix may be). t

[0035] Therefore, the method of the present invention involves varying the angle between a first liquid crystal alignment direction and a second liquid crystal alignment direction in a lenticular device, thereby determining an angle that minimizes or (for the viewer) makes acceptable the generation of disclinations after switching from the first view mode to the second view mode.

[0036] ​In practice, this typically results in changing the angle between the polarization direction of a linear polarizer in the display panel and the first liquid crystal alignment direction, since the polarization direction of the linear polarizer in the display panel and the second liquid crystal alignment direction are coupled (unless a polarization rotator is present as explained above).

[0037] The result of the method of the present invention is displayed diagrammatically in FIG. 4, where the second liquid crystal alignment direction and display polarization are aligned at a smaller angle α p The same lenticular device as in FIG. 3 is shown, except that the helical twist α t is accordingly reduced (the angle and inclination α s remains unchanged). This reduced helical twist angle α t was obtained after it was determined that no disclination occurs after switching from the first to the second viewing mode (see also the examples). The two opposite arrows on either side of the polarization direction indicate the angle α p It is shown that an iterative process of varying x multiple times can be applied, and after each round the occurrence of disclinations is determined and a decision is made whether to proceed with angle optimization.

[0038] In the method of the present invention, the occurrence of disclinations being minimal or the occurrence of disclinations being tolerable means that at least one of the following is included. the minimum or permissible size of the disclinations, the minimum or permissible number of disclinations (where the number is, for example, the number per autostereoscopic display device or the number per unit of surface area of ​​the array of lenticular elements), - The minimum or acceptable duration of disclinations.

[0039] In this specification, the term "minimal occurrence of disclinations" may also include the complete absence of disclinations.

[0040] Typically, minimizing the occurrence of disclinations includes minimizing the size, number, and duration of the disclinations.

[0041] Typically, allowing the occurrence of disclinations includes allowing the size, number, and duration of the disclinations.

[0042] Those skilled in the art know how to implement the method of the present invention (specifically, determining the optimal angle, i.e., the angle that allows the occurrence of disclinations) by routine experimentation without inventive effort, as demonstrated by the examples. For example, creating an experimental setup where the angle can be varied, or manufacturing multiple autostereoscopic display devices each having a different angle. For all angles, perform the switching of the autostereoscopic display device and then observe whether disclinations are formed, specifically, whether their size, number, and / or duration follow a specific trend towards a specific minimum value.

[0043] The angle between the two alignment directions preferably varies by varying the second liquid crystal alignment direction with respect to the rest of the autostereoscopic display device. In other words, varying the angle between the first and second liquid crystal alignment directions in the lenticular device preferably includes varying the second liquid crystal alignment direction with respect to the display panel and with respect to the first liquid crystal alignment direction.

[0044] Typically, since it is necessary to align both directions, this includes simultaneously varying the polarization directions of the linear polarizers to the same extent. Thus, varying the angle between both directions of the liquid crystal alignment may further include varying the polarization direction of the linear polarizer to the same extent as the second liquid crystal alignment direction is varied so that the second liquid crystal alignment direction (still) coincides with the polarization direction of the linear polarizer.

[0045] However, as described above, it is also possible to position the polarization rotator between the linear polarizer and the second inner surface. Thereby, since the mismatch between the polarization direction and the liquid crystal alignment direction can be compensated, it is not necessary to change the polarization direction of the linear polarizer simultaneously.

[0046] There is another possibility of changing the angle by changing the first liquid crystal alignment direction with respect to the rest of the autostereoscopic display. In other words, changing the angle between the first liquid crystal alignment direction and the second liquid crystal alignment direction in the lenticular device then involves changing the first liquid crystal alignment direction with respect to the display panel and with respect to the second liquid crystal alignment direction.

[0047] However, since it is highly preferable that the liquid crystal alignment on the lenticular is in the elongated direction of the lenticular, changing the first liquid crystal alignment direction almost inevitably requires changing the direction of the lenticular (i.e., their inclination) by the same amount. However, it is not desirable to change the direction of the lenticular with respect to the rest of the device (and thus with respect to the pixel array). This is because only a few combinations of pixel pitch and lenticular inclination are possible for the lenticular liquid crystal cell to operate well, and most combinations do not result in usable imaging. Also, the choice of pixel pitch and the corresponding lenticular inclination determines the resolution and the optimal viewing distance in the 3D viewing mode. Furthermore, the range within which the inclination can be changed is 80° (i.e., 0 to 40° on both sides of the vertical direction), and thus the optimal helical twist cannot be accessed even if an inclination outside this range is required.

[0048] Thus, in summary, while varying the angle between the two alignment directions, the relative positioning between the lenticular array and the array of display pixel elements remains invariant, i.e., it is highly preferable to vary the second liquid crystal alignment direction with respect to the rest of the autostereoscopic display. In the absence of a polarization rotator, the polarization direction of the linear polarizer needs to change accordingly. In the presence of a polarization rotator, since the polarization rotator can overcome the mismatch between the two directions, the two directions can be selected independently of each other.

[0049] When the display panel is a liquid crystal display (LCD), since the linear polarizer needs to be integrated into the display panel, changing the polarization direction of the linear polarizer typically requires a new design of the LCD. However, this does not apply when the display panel is an organic light-emitting diode (OLED) display because OLEDs do not require a polarizer to generate the display output. As a result, the polarization direction of the linear polarizer can be freely selected without the need to redesign the OLED display device. Thus, the display panel in the method of the present invention preferably includes an OLED display device rather than an LCD.

[0050] However, the drawback of using an LCD can be alleviated when a polarization rotator is used, because this allows the second liquid crystal alignment direction to be selected independently of the polarization direction of the linear polarizer incorporated into the LCD.

[0051] The display panel may include a liquid crystal display (LCD) or an organic light emitting diode (OLED) display device. If the display panel includes an OLED display device, it preferably also includes a quarter-wave plate. This is because such a plate functions as an anti-reflection means for the viewer in combination with a linear polarizer within the display panel. Without such means, the OLED display device may function as a mirror. The reflection of ambient light caused by such a mirror is usually visible to the viewer of an autostereoscopic display device, and the viewer is likely to experience this as an interference. The displayed image loses contrast and / or blackness due to the additional light of the reflection.

[0052] The present invention further relates to an autostereoscopic display device that is electrically switchable between a first view mode and a second view mode, the device having an angle between a first liquid crystal alignment direction and a second liquid crystal alignment direction that results in a minimal or acceptable occurrence of disclination after switching from the first view mode to the second view mode. Such a device is typically a device used in the method described above.

[0053] The display panel may include a liquid crystal display (LCD) or an organic light emitting diode (OLED) display device. For the same reason outlined above, the display panel preferably includes an OLED display device.

[0054] Disclination seems to occur particularly when the angle between the first liquid crystal alignment direction and the second liquid crystal alignment direction is 0° or 90°. Disclination usually also occurs when the angle is between 0° and 4° or between 86° and 90°.

[0055] Therefore, in the autostereoscopic display device of the present invention, the angle between the first liquid crystal alignment direction and the second liquid crystal alignment direction is within the range of 4° to 86°, specifically within the range of 5° to 85°.

[0056] More specifically, it has been found that an angle of less than 45° is effective in reducing disclination. Therefore, the angle is preferably in the range of 5 to 40°, for example, in the range of 5 to 35°, 5 to 30°, 5 to 25°, 5 to 20° or 5 to 15°. More preferably, it is in the range of 10 to 25°, for example, in the range of 10 to 20°.

[0057] In the autostereoscopic display device of the present invention, the polarization rotator is positioned between the linear polarizer and the second inner surface, and can compensate for the mismatch between 1) the polarization direction of the linear polarizer and 2) the second liquid crystal alignment direction.

[0058] Normally, the shortest distance between the first inner surface and the second inner surface is in the range of 5.0 to 50 μm. This is typically the distance between the apex of the lenticular element and the (flat) second optically transparent substrate.

Example

[0059] 1. An autostereoscopic display device for comparison known in the art. A switchable autostereoscopic display device with a diagonal diameter of 15.6 inches was prepared. The cell gap between the upper part of the lens (lenticular apex) and the opposing plate is 10 microns and includes a liquid crystal medium having a birefringence of 0.12. The device has a horizontal display polarization, that is, the display output has horizontal polarization when it encounters the liquid crystal medium. Further, the device has a lenticular tilt angle α of 16.7° with respect to the vertical axis s In the liquid crystal alignment in the same direction as this tilt direction, the twist α of the helically arranged liquid crystal molecules is 73.3° over the entire cell gap (between the first inner surface and the second inner surface). t becomes 73.3°.

[0060] This is schematically shown in FIG. 3, which is aligned horizontally along the horizontal display polarization at an angle α with respect to the vertical (α p = 90°) foreground plate (5), and at an angle α with respect to the vertical p = 90°) foreground plate (5), and at an angle α with respect to the vertical sHere, a background plate (4) aligned in the tilt direction (α s = 16.7°) is shown. The overall twist α t between both plates (4, 5) is shown by 10 steps (α t = 73.3°) that gradually thin towards the background plate, like the steps of a spiral staircase.

[0061] This autostereoscopic display device shows very persistent disclinations after switching from the first view mode (a helical liquid crystal alignment along a spiral axis perpendicular to the planar electrodes) to the second view mode (a liquid crystal alignment perpendicular to the planar electrodes). These disclinations are shown in the micrograph of FIG. 5. The regular shape (12) from left to right represents a lenticular, and the curve (13) represents the boundary between different liquid crystal domains having different liquid crystal orientations (i.e., they represent the actual disclinations). To clear the disclinations, a lamp voltage was applied for a period of 20 seconds before reaching the final switching voltage. During that period, significant crosstalk was observed. This was only well reduced to normal and acceptable values after that period. Furthermore, it was observed that some disclinations persisted even after reaching the final switching voltage.

[0062] 2. The autostereoscopic display device of the present invention. The method of the present invention was applied to reach a display device that shows fewer disclinations when switching from the first view mode to the second view mode. For this purpose, an autostereoscopic display device having a display polarization α p = 32° with respect to the vertical axis and generating a twist α t = 15.3° (subtracted 16.7° of the tilt direction from 32° of the display polarization) was prepared. In this cell, no disclinations appeared during or after switching. Furthermore, the switching delay (lamp voltage) did not seem to be necessary, and no initial increase in crosstalk was observed.

[0063] This is shown in Figure 4, where the liquid crystal alignment and the direction of the display polarization are at an angle α of 32°, rather than 90° as in Figure 3. p This results in a twist α of 15.3°, rather than 73.3° as in Figure 3. t This smaller twist α t is preferable as, in contrast to the larger twist of Figure 3, it does not give rise to disclinations.

[0064] Thus, the autostereoscopic display device according to the invention basically shows no disclination upon switching, which significantly improves upon known 2D / 3D - switchable autostereoscopic display devices.

Claims

1. A method for reducing disclination in an autostereoscopic display device (11) that can be electrically switched from a first view mode to a second view mode, wherein the autostereoscopic display device (11) comprises: - A display panel (1), ○ An array of display pixel elements for generating a display output, ○ A linear polarizer configured to filter the display output in a clearly defined polarization direction, and a display panel (1); - A lenticular device (2) provided on the display panel (1) and electrically switchable to provide the first view mode or the second view mode, wherein the lenticular device (2) comprises: ○ A first optically transparent substrate (4) comprising an array of lenticular elements having a first inner surface (4a) with liquid crystal alignment characteristics having a first liquid crystal alignment direction, ○ A second optically transparent substrate (5), - An outer surface (5b) configured to receive the display output facing the linear polarizer, - A second inner surface (5a) having liquid crystal alignment characteristics having a second liquid crystal alignment direction that coincides with the polarization direction of the linear polarizer, wherein the first inner surface (4a) and the second inner surface (5a) face each other, and a second optically transparent substrate (5); ○ A first planar switching electrode (6) disposed on the side of the first optically transparent substrate (4), ○ A second planar switching electrode (7) disposed on the side of the second optically transparent substrate (5), ○ A liquid crystal medium (8) containing liquid crystal molecules (9), wherein the liquid crystal medium (8) is sandwiched between the two substrates (4, 5) and is in contact with the first inner surface (4a) and the second inner surface (5a), - In the first view mode, the liquid crystal molecules (9) are in the plane of the two planar switching electrodes (6, 7), and - In the second view mode, the liquid crystal molecules (9) are oriented perpendicular to the two planar switching electrodes (6, 7), a lenticular device (2); - Means (3) for applying a switching voltage to both ends of both planar switching electrodes (6, 7) to achieve the switching from the first view mode to the second view mode. In the first view mode, the liquid crystal molecules (9) define a helix (10) having a twist defined by the angle between the first liquid crystal alignment direction and the second liquid crystal alignment direction. The method includes changing the angle between the first liquid crystal alignment direction and the second liquid crystal alignment direction in the lenticular device (2), thereby determining an angle that results in a minimal or acceptable occurrence of disclination after switching from the first view mode to the second view mode. **Claim 2** The minimal or acceptable occurrence of disclination - the minimal or acceptable size of the disclination, - the minimal or acceptable number of disclinations, - the minimal or acceptable duration of the disclination, and includes at least one of them, the method according to claim 1. **Claim 3** The display panel (1) includes a liquid crystal display device (LCD), the method according to claim 1 or 2. **Claim 4** The display panel (1) includes an organic light emitting diode (OLED) display device, the method according to claim 1 or 2. **Claim 5** The display panel (1) includes an OLED display device and a quarter-wave plate, the method according to claim 4. **Claim 6** Changing the angle between the first liquid crystal alignment direction and the second liquid crystal alignment direction in the lenticular device (2) includes changing the second liquid crystal alignment direction with respect to the display panel (1) and with respect to the first liquid crystal alignment direction, the method according to any one of claims 1 to 5. **Claim 7** Changing the angle further includes changing the polarization direction of the linear polarizer to the same extent as changing the second liquid crystal alignment direction, the method according to claim 6. **Claim 8** A polarization rotator is positioned between the linear polarizer and the second inner surface (5a), and the polarization rotator compensates for the mismatch between 1) the polarization direction of the linear polarizer and 2) the second liquid crystal alignment direction, the method according to any one of claims 1 to 7. **Claim 9** Changing the angle between the first liquid crystal alignment direction and the second liquid crystal alignment direction in the lenticular device (2) includes changing the first liquid crystal alignment direction with respect to the display panel (1) and with respect to the second liquid crystal alignment direction, the method according to any one of claims 1 to 8.

10. An auto-stereoscopic display device (11) that can be electrically switched from a first view mode to a second view mode, wherein the auto-stereoscopic display device (11) comprises: - A display panel (1), ○ An array of display pixel elements for generating a display output, ○ A linear polarizer configured to filter the display output in a clearly defined polarization direction, and a display panel (1); - A lenticular device (2) provided on the display panel and electrically switchable to provide the first view mode or the second view mode, wherein the lenticular device (2) comprises: ○ A first optically transparent substrate (4) comprising an array of lenticular elements having a first inner surface (4a) with liquid crystal alignment characteristics having a first liquid crystal alignment direction, ○ A second optically transparent substrate (5), - An outer surface (5b) configured to receive the display output facing the linear polarizer, - A second inner surface (5a) having liquid crystal alignment characteristics having a second liquid crystal alignment direction that coincides with the polarization direction of the linear polarizer, and the first inner surface (4a) and the second inner surface (5a) face each other, and a second optically transparent substrate (5) having a second inner surface (5a); ○ A first planar switching electrode (6) disposed on the side of the first optically transparent substrate (4), ○ A second planar switching electrode (7) disposed on the side of the second optically transparent substrate (5), ○ A liquid crystal medium (8) containing liquid crystal molecules (9), and the liquid crystal medium (8) is sandwiched between the two substrates (4, 5) and is in contact with the first inner surface (4a) and the second inner surface (5a), - In the first view mode, the liquid crystal molecules (9) are in the plane of the two planar switching electrodes (6, 7), and - In the second view mode, the liquid crystal molecules (9) are oriented perpendicular to the two planar switching electrodes (6, 7), and a lenticular device (2); - Means (3) for applying a switching voltage to both ends of both planar switching electrodes (6, 7) to achieve switching from the first view mode to the second view mode. - In the first view mode, the liquid crystal molecules (9) define a helix (10) having a twist defined by an angle between the first liquid crystal alignment direction and the second liquid crystal alignment direction. - The angle between the first liquid crystal alignment direction and the second liquid crystal alignment direction is in the range of 4 to 86°, autostereoscopic display device (11).

11. The display panel (1) includes a liquid crystal display device (LCD), the autostereoscopic display device (11) according to claim 10.

12. The display panel (1) includes an organic light emitting diode (OLED) display device, the autostereoscopic display device (11) according to claim 10.

13. The angle between the first liquid crystal alignment direction and the second liquid crystal alignment direction is in the range of 5 to 35°, the autostereoscopic display device (11) according to any one of claims 10 to 12.

14. The angle between the first liquid crystal alignment direction and the second liquid crystal alignment direction is in the range of 5 to 25°, specifically in the range of 10 to 20°, the autostereoscopic display device (11) according to any one of claims 10 to 12.

15. A polarization rotator is positioned between the linear polarizer and the second inner surface (5a), and the polarization rotator compensates for the mismatch between 1) the polarization direction of the linear polarizer and 2) the second liquid crystal alignment direction, the autostereoscopic display device (11) according to any one of claims 10 to 14.

16. The shortest distance between the first inner surface (4a) and the second inner surface (5a) is in the range of 5.0 to 50 μm, the autostereoscopic display device (11) according to any one of claims 10 to 15.

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