Method for reducing disalignment in 2D / 3D switchable naked eye stereoscopic display

Abstract

The present invention relates to a method for reducing the occurrence of misalignment in a naked eye stereoscopic display device capable of electrically switching between a 2D view mode and a 3D view mode wherein the method comprises changing the angle between two directions of liquid crystal alignment in a convex lens device, thereby, an angle that results in a minimum or acceptable error upon switching between the two view modes is determined. The invention also relates to a naked eye stereoscopic display device with reduced misalignment when switching between two view modes.

Description

Technical Field

[0001] The present invention relates to a method for reducing disclination occurring in a naked-eye stereoscopic display device capable of electrically switching from a first viewing mode to a second viewing mode; and to a naked-eye stereoscopic display device capable of electrically switching from a first viewing mode to a second viewing mode. Background Art

[0002] Displays that can be electrically switched between a two-dimensional viewing mode and a three-dimensional viewing mode, often referred to as 2D / 3D switchable autostereoscopic displays, have attracted great interest in the past two decades. A common approach is to align a lenticular device with a pixel array, the lenticular device comprising an array of semi-cylindrical microlenses (lenticular lenses) adjacent to a liquid crystal medium that can be switched between two liquid crystal orientations under the influence of an electric field. In a first orientation, the director of the liquid crystal medium is in the plane of the display; and in a second orientation, the director of the liquid crystal medium is perpendicular to the plane of the display.

[0003] In this arrangement, each convex lens is associated with a group of at least two rows of (sub) pixels that extend parallel to the lens or at an angle (tilt) to the lens. The pixel output propagated through the convex lens device is affected by the optical properties of the convex lens and the liquid crystal medium. The refractive index of the convex lens is fixed, but the refractive index of the adjacent liquid crystal medium can be switched between two values ​​by switching between two liquid crystal orientations; 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. Since the pixel output propagates substantially perpendicular to the display plane, it experiences the first refractive index or the second refractive index. In the first view mode, the liquid crystal medium is in the first orientation. Its refractive index matches the refractive index of the convex lens, so that the convex lens loses its focusing effect and makes the convex lens device appear as a transparent and flat optical panel. This forms a two-dimensional view mode of a naked-eye stereoscopic display. In the second view mode, the liquid crystal medium is in the second liquid crystal orientation. The refractive index does not match, which makes each convex lens exhibit a focusing effect. This makes it possible to direct the output from different rows of pixels to different spatial locations in front of the display, which in turn allows the viewer to perceive a three-dimensional image consisting of a left image and a right image. This forms a three-dimensional viewing mode for a naked-eye stereoscopic display. It will therefore be clear that in the design of a display that can switch between a two-dimensional viewing mode and a three-dimensional viewing mode, well-controlled switching between liquid crystal orientations becomes crucial.

[0004] Switching from one liquid crystal orientation to another can occur by changing the electric field to which the liquid crystal material is subjected. This usually requires applying an electric field (in the absence of an electric field) or switching off the electric field (in the presence of an electric field). It is important that the liquid crystal orientation changes uniformly upon such a change in the electric field. However, this is usually not the case. It is then observed that different domains with different liquid crystal orientations 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 are generated at the disclinations. This leads to increased crosstalk when switching to 3D viewing mode and reduced image quality when switching to 2D viewing mode.

[0005] In conventional electrically switchable 2D / 3D displays, there is the problem of disclinations, which form when switching from one liquid crystal orientation to another. Furthermore, this is usually not limited to a single occurrence in a particular display. Disclinations may occur at multiple locations in the display. In addition to the formation of disclinations, the duration of disclinations is also an issue, as many disclinations exist for a long time, such as more than a minute, more than ten minutes, or even permanently.

[0006] To date, some measures have been taken 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 slope so that the switching occurs gradually rather than instantaneously (see, for example, WO2020135731). Although this alleviates the problem to a certain extent, its implementation still has shortcomings.

[0007] One particular drawback is that switching 2D / 3D takes more time when a voltage ramp is used. During this time, typically 5 to 30 seconds, the performance of the display is impaired, and in particular the level of crosstalk increases. Moreover, a specific voltage ramp must be carefully programmed and tested for each new model, and variations in the production process can easily lead to a mismatch between the behavior of the liquid crystal medium and the voltage ramp. Summary of the invention

[0008] Therefore, it is an object of the present invention to provide a 2D / 3D display capable of electrical switching, which does not form disclinations when switching, or at least forms disclinations to a lesser extent than in known switching procedures. For example, the size, number and / or duration of disclinations are reduced. Another object of the present invention is to make disclinations exist only for a short time span that is not considered a problem. Another object of the present invention is to provide a solution that is simpler than solutions known in the art. More generally, it is an object of the present invention to improve the viewing experience of viewers of naked-eye stereoscopic displays.

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

[0010] Therefore, the present invention relates to a method for reducing disclination occurring in a naked-eye stereoscopic display device (11) capable of being electrically switched between a first viewing mode and a second viewing mode, the naked-eye stereoscopic display device (11) comprising:

[0011] A display panel (1), comprising:

[0012] An array of display pixel elements for generating a display output;

[0013] a linear polarizer configured to filter the display output into a well-defined polarization direction;

[0014] A convex lens device (2) is arranged above a display panel (1), wherein the display panel (1) is electrically switchable to provide a first viewing mode or a second viewing mode, and the convex lens device (2) comprises:

[0015] a first optically transparent substrate (4) comprising an array of convex lens elements, wherein the convex lens elements have a first inner surface (4a), the first inner surface (4a) having liquid crystal alignment properties including a first liquid crystal alignment direction;

[0016] A second optically transparent substrate (5) having:

[0017] an outer surface (5b) facing the linear polarizer and configured to receive a display output;

[0018] a second inner surface (5a) having a liquid crystal alignment property including a second liquid crystal alignment direction, wherein the second liquid crystal alignment direction is consistent with the polarization direction of the linear polarizer, the first inner surface (4a) and the second inner surface (5a) facing each other;

[0019] A first plane switching electrode (6) disposed on one side of the first optically transparent substrate (4);

[0020] A second plane switching electrode (7) disposed on one side of the second optically transparent substrate (5);

[0021] A liquid crystal medium (8) comprising liquid crystal molecules (9) sandwiched between two substrates (4, 5)

[0022] and in contact with the first inner surface (4a) and the second inner surface (5a), wherein

[0023] In a first viewing mode, the liquid crystal molecules (9) are located in the plane of the two plane switching electrodes (6, 7); and

[0024] In the second viewing mode, the liquid crystal molecules (9) are oriented perpendicularly to the two plane switching electrodes (6, 7);

[0025] A component (3) for applying a switching voltage to two planar switching electrodes (6, 7) to achieve switching from a first viewing mode to a second viewing mode;

[0026] wherein, in a first view mode, the liquid crystal molecules (9) define a helix (10) having a helical twist, the helical twist being defined by an angle between a first liquid crystal alignment direction and a second liquid crystal alignment direction;

[0027] The method comprises changing the angle between a first liquid crystal alignment direction and a second liquid crystal alignment direction in a convex lens device (2) to determine an angle causing a minimum disclination or an acceptable disclination after switching from a first viewing mode to a second viewing mode.

[0028] The present invention further relates to a naked-eye stereoscopic display device (11) capable of electrically switching from a first viewing mode to a second viewing mode, the naked-eye stereoscopic display device (11) comprising:

[0029] A display panel (1), comprising:

[0030] An array of display pixel elements for generating a display output;

[0031] a linear polarizer configured to filter the display output into a well-defined polarization direction;

[0032] A convex lens device (2) is arranged above a display panel, the display panel being electrically switchable to provide a first viewing mode or a second viewing mode, the convex lens device (2) comprising:

[0033] a first optically transparent substrate (4) comprising an array of convex lens elements, wherein the convex lens elements have a first inner surface (4a), the first inner surface (4a) having liquid crystal alignment properties including a first liquid crystal alignment direction;

[0034] A second optically transparent substrate (5) having:

[0035] an outer surface (5b) facing the linear polarizer and configured to receive a display output;

[0036] a second inner surface (5a) having a liquid crystal alignment property including a second liquid crystal alignment direction, the second liquid crystal alignment direction being consistent with the polarization direction of the linear polarizer, the first inner surface (4a) and the second inner surface (5a) facing each other;

[0037] A first plane switching electrode (6) disposed on one side of the first optically transparent substrate (4);

[0038] A second plane switching electrode (7) disposed on one side of the second optically transparent substrate (5);

[0039] A liquid crystal medium (8) comprising liquid crystal molecules (9) sandwiched between two substrates (4, 5)

[0040] and in contact with the first inner surface (4a) and the second inner surface (5a), wherein

[0041] In a first viewing mode, the liquid crystal molecules (9) are located in the plane of the two plane switching electrodes (6, 7); and

[0042] In the second viewing mode, the liquid crystal molecules (9) are oriented perpendicularly to the two plane switching electrodes (6, 7);

[0043] A component (3) for applying a switching voltage to two planar switching electrodes (6, 7) to achieve switching from a first viewing mode to a second viewing mode;

[0044] in

[0045] In a first view mode, the liquid crystal molecules (9) define a helix (10) having a helical twist, the helical twist being defined by an angle between a first liquid crystal alignment direction and a second liquid crystal alignment direction;

[0046] An angle between the first liquid crystal alignment direction and the second liquid crystal alignment direction is in a range of 4° to 86°.

[0047] The angle is in particular an angle that results in a minimum disclination or an acceptable disclination after the naked-eye stereoscopic display device (11) is switched from the first viewing mode to the second viewing mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 A known autostereoscopic display device (11) is schematically shown in a first viewing mode.

[0049] Figure 2 A known autostereoscopic display device (11) is schematically shown in a second viewing mode.

[0050] Figure 3 Shows Figure 1 A simplified illustration of a convex lens device (2) of a naked-eye stereoscopic display device (11).

[0051] Figure 4 A simplified illustration of a lenticular device (2) obtained according to the method of the invention is shown.

[0052] Figure 5is a microscope image of a known lenticular lens arrangement (2) which disclinates after switching from a first viewing mode to a second viewing mode. DETAILED DESCRIPTION

[0053] The elements shown in the figures are shown for simplicity and clarity and are not necessarily drawn to scale. For example, the size of some 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 sizes of the liquid crystal molecular schematics and the convex lens elements relative to other components of the naked eye stereoscopic display device cannot be derived from the figures. In addition, the angles that can be derived from the figures are not necessarily the same as the example values ​​of these angles listed in the specification.

[0054] Furthermore, the terms "first", "second" and the like in the description and the claims are generally used to distinguish between similar elements and not necessarily to describe a sequential or order of events.

[0055] In the context of the present invention, the term "viewer" refers to a person who may consume (particularly watch) content presented by a naked-eye stereoscopic display device. Throughout the text, references to the viewer will use masculine terms such as "he", "him" or "his". This is only for the purpose of clarity and brevity, and it should be understood that feminine terms such as "she" and "her" are equally applicable.

[0056] In the context of the present invention, the term "twist" or "helical twist" refers to the absolute angle and the total angle of the helical twist, which is determined from the starting point of the helix to the end point of the helix. In known lenticular devices, the twist of the helix formed by the liquid crystal molecules is usually between 0° and 180°, in particular between 0° and 90°. In the lenticular device (2) according to the present invention, the twist is in the range of 4° to 86°. Since the helix exists between the first inner surface (4a) and the second inner surface (5a), the starting point and the end point of the helix are marked by these two surfaces.

[0057] It will be appreciated that the liquid crystal medium is a birefringent material having a first refractive index for light travelling along the director of the liquid crystal medium and a second refractive index for light travelling perpendicular to the director of the liquid crystal medium. When the term "refractive index" is used throughout the text with respect to the liquid crystal medium, then unless explicitly stated otherwise, this refers to the refractive index of the liquid crystal medium in a direction perpendicular to the planar switching electrodes (i.e., in the direction of travel of the display output). The refractive index may refer to the first refractive index or the second refractive index as defined above, depending on the electric field applied to the liquid crystal medium.

[0058] The naked eye stereoscopic display device (11) used in the method of the present invention comprises three main components (1, 2, 3). These components are also Figure 1 and Figure 2 It shows:

[0059] A display panel (1) for providing a linearly polarized display output (i.e., light);

[0060] A lenticular lens device (2) is arranged above a display panel (1), wherein the display panel (1) can switch between different optical properties, including providing the linearly polarized pixel output as a single image (two-dimensional view) to a viewer, or providing the linearly polarized pixel output as a left image and a right image (three-dimensional view or naked eye stereoscopic view) to a viewer;

[0061] Means (3) for applying a switching voltage between two planar switching electrodes (6, 7) to allow switching between the two optical properties.

[0062] In a lenticular device (2), a liquid crystal medium (8) is located between two opposing surfaces, i.e., the liquid crystal medium (8) is in contact with both surfaces. This relates to a first inner surface (4a), which is a lenticular surface of an array of lenticular elements (this array being part of a first optically transparent substrate); and to a second inner surface (4b), which is a flat surface of a second optically transparent substrate. The two inner surfaces (4a, 4b) have liquid crystal alignment properties; the liquid crystal alignment properties of the first inner surface (4a) include a first liquid crystal alignment direction, and the liquid crystal alignment properties of the second inner surface (4b) include a second liquid crystal alignment direction. The display output enters the liquid crystal medium (8) through its interface with the second inner surface (4b) and is output from the liquid crystal medium (8) through its interface with the first inner surface (4a). The display output then travels through the lenticular elements.

[0063] Preferably, the first liquid crystal alignment direction (which is on the convex lens surface) is generally parallel to the longitudinal direction of the convex lens element. This is because the introduction of the liquid crystal alignment direction is performed by rubbing the surface in the direction for alignment. When it is necessary to rub the surface of the convex lens element, rubbing in the convex lens direction is more advantageous than rubbing at an angle to the convex lens direction.

[0064] The first optically transparent substrate (4) has an outer surface facing a viewer of the naked-eye stereoscopic display device (11), and the second optically transparent substrate (5) has an outer surface facing the display element (1).

[0065] The liquid crystal medium (8) comprises liquid crystal molecules (9). Two plane switching electrodes (6, 7) are positioned on either side of the liquid crystal medium (8) so that they can apply an electric field to the liquid crystal medium (8). The liquid crystal molecules (9) can be oriented in the plane of the plane switching electrodes (6, 7) under the influence of the orientation properties of the two surfaces; or perpendicular to the plane of the plane switching electrodes (6, 7) under the influence of the voltage applied to the two switching electrodes (6, 7). When the voltage is sufficiently low, preferably completely absent, the liquid crystal molecules can return to an orientation in the plane of the plane switching electrodes and follow the orientation properties of the two surfaces.

[0066] Figure 1 and Figure 2 The plane orientation and normal orientation are shown respectively. Figure 1 and Figure 2 It is a cross-sectional view of a known naked-eye stereoscopic display device (11). Figure 1 The extension direction of the liquid crystal molecules (9) in the structure is located in a plane parallel to the plane of the planar switching electrode (first view mode). No voltage is applied to the structure (3). The liquid crystal molecules (9) have a changing direction in this plane, which is manifested by the liquid crystal molecules (9) existing in the form of a helix (10), as will be further described below. Figure 2 The extension direction of the liquid crystal molecules (9) in the substrate is perpendicular to the plane of the planar switching electrode (second view mode). The AC switching voltage is applied to the component (3).

[0067] In the absence of an electric potential, the molecules are oriented in the plane of the planar switching electrode and according to the liquid crystal alignment properties of the first surface and the second surface, thereby defining a first view mode. When a sufficiently strong electric potential ("switching voltage") is applied, the molecules switch to an orientation consistent with the corresponding electric field, which is perpendicular to the plane orientation of the planar switching electrode, thereby defining a second view mode. Therefore, the switching voltage is the voltage at which the naked eye stereoscopic display device changes to the second view mode and remains in the second view mode. There is usually a threshold voltage, above which it switches to the second view mode. Therefore, the switching voltage is in principle any voltage above the threshold voltage.

[0068] The naked eye stereoscopic display device may be configured such that the first view mode corresponds to the optical property of providing a two-dimensional view; and the second view mode corresponds to the optical property of providing a three-dimensional view. Alternatively, it may be configured such that the first view mode corresponds to the optical property of providing a three-dimensional view; and the second view mode corresponds to the optical property of providing a two-dimensional view.

[0069] In a viewing mode providing a three-dimensional view, the lenticular lens device (2) comprises optical properties which allow display outputs from different display pixel elements to be directed to different spatial positions within the field of view of the naked-eye stereoscopic display device (11), thereby allowing a stereoscopic image consisting of a left image and a right image to be displayed.

[0070] As described above, the liquid crystal medium is sandwiched between two surfaces (i.e., a first inner surface and a second inner surface), each of which has a liquid crystal alignment property. The display output of the display panel first passes through the second inner surface and then through the first inner surface. The liquid crystal alignment of the second inner surface (i.e., the second liquid crystal alignment direction) must be consistent with the polarization direction of the linear polarizer, so that 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 "experiences" the expected refractive index of the liquid crystal medium.

[0071] However, there is an exception to the above statement about the polarization direction of the linear polarizer being the same as the second liquid crystal alignment direction. This is the case when a so-called "polarization rotator" is positioned between the linear polarizer and the second inner surface, which is a member capable of rotating the polarization direction of light traveling through it. The polarization rotator will then rotate the polarization direction of the light emerging from the linear polarizer to the second liquid crystal alignment direction. Such a polarization rotator can be provided as a foil or optical plate, wherein the rotation property is contained in the material of the foil or optical plate; or such a polarization rotator can also be provided in the form of a liquid crystal cell, which operates by the same spiral liquid crystal alignment principle as in the lenticular device of the present invention (except, of course, for the lack of lenticular elements).

[0072] However, it is not necessary for the first inner surface from which the display output is output from the liquid crystal medium to coincide with the angle of the polarization direction of the display output. The first inner surface may have an alignment property in another direction different from that of the second inner surface. Therefore, the liquid crystal molecules stacked between the two surfaces gradually follow this direction change by forming a spiral. In, for example, Figure 1 Pictured in the middle, Figure 1 A naked-eye stereoscopic display device (11) comprising a convex lens device (2) is shown, wherein a helix can be seen from the side, with its helical axis parallel to the plane shown in the figure and perpendicular to the plane of the planar switching electrode (the obviously shorter molecule (9) is not in the plane shown in the figure, while the obviously longest molecule (9) is in the plane shown in the figure). Thus, the helical twist angle α of the helix is t It is defined as the angle between the directions of the two liquid crystal alignments (the angle between the two terminal molecules at each end of the helix). Figure 3 , where the helical axis is perpendicular to the plane of the drawing ( Figure 3 will be further described below).

[0073] As long as the angle between two adjacent liquid crystal molecules in the spiral does not exceed a certain (quantum mechanically defined) angle, the polarization of the display output will follow the direction of the long molecular axis of the liquid crystal molecules and propagate along the spiral structure towards the first inner surface. In this way, the movement of the display output through the liquid crystal medium actually changes the polarization direction of the display output. In this way, the angle between the two alignment directions has no effect on the optical properties of the convex lens device (at least on the properties related to the normal operation of the naked eye stereoscopic display device). When this requirement is met, the angle between the two alignment directions can in principle be any angle between 0° and 180°.

[0074] Figure 3 Shows Figure 1 A simplified illustration of a convex lens device (2) showing only the first optically transparent substrate (4) and the second optically transparent substrate (5), which are parallel to the illustration plane. For clarity, Figure 3 The array of lenticular elements is not shown. The second optically transparent substrate (5) is shown in the foreground and has a horizontal liquid crystal alignment and a horizontal display polarization, which are at an angle α to the vertical. p The first optically transparent substrate (4) is shown in the background and has a liquid crystal alignment in a tilt direction, which makes an angle α with the vertical line. s The total twist angle α of the helix t Represented by ten steps fading toward the background plate. This representation is similar to the steps of a spiral staircase viewed from above.

[0075] However, the inventors have found that when switching from the first view mode to the second view mode, that is, when the liquid crystal molecules switch from an orientation in the plane of the switching electrodes (with a specific spiral stack) to an orientation perpendicular to the two plane switching electrodes, some angles between the two alignment directions cause more disclinations than other angles. This suggests that an optimal angle can be obtained between the two alignment directions, thereby minimizing or even completely eliminating the problem of disclinations. Specifically, this suggests that one or more of the following occurs: a reduction in the size of the disclinations, a reduction in the number of disclinations (e.g., calculated per switching event per naked-eye stereoscopic display device), and a reduction in the duration of the disclinations.

[0076] Switching in the opposite direction (ie, from the second view mode to the first view mode) generally does not induce unwanted disclination (regardless of whether the helix is ​​actually twisted α t how).

[0077] Therefore, the method of the present invention includes changing the angle between the first liquid crystal alignment direction and the second liquid crystal alignment direction in the convex lens device, thereby determining the angle that causes the minimum occurrence rate or acceptable occurrence rate (for the viewer) of disclination after switching from the first viewing mode to the second viewing mode.

[0078] In practice, this typically boils down to 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 is coupled to the second liquid crystal alignment direction (unless a polarization rotator is present as described above).

[0079] Figure 4 The results of the method of the invention are schematically shown. The convex lens device shown here is Figure 3 The convex lens device is the same as in the embodiment, except that the second liquid crystal alignment direction and the angle α between the display polarization and the vertical line p This results in a twist of the helix α t Correspondingly reduced (because the angle of the first liquid crystal alignment direction and the tilt angle α s The twist angle α of the helix t The reduction in the angle α is obtained when it is determined that no disclination occurs after switching from the first viewing mode to the second viewing mode (see also the example). The two opposite arrows on both sides of the polarization direction indicate that an iterative process can be used, in which the angle α is changed multiple times. p ; After each change, determine whether disclination has occurred and decide whether to continue optimizing the angle.

[0080] In the method of the present invention, the minimum occurrence rate or acceptable occurrence rate of disclination means at least one of the following conditions:

[0081] the minimum or acceptable size of disclination;

[0082] a minimum number or an acceptable number of disclinations (where the number is calculated, for example, per number per autostereoscopic display device or per unit surface area of ​​an array of lenticular elements);

[0083] The minimum duration or acceptable duration of a disclination.

[0084] In this context, the term "minimal occurrence of disclinations" may also include the complete absence of disclinations.

[0085] Generally, the minimum occurrence rate of disclinations includes the minimum size, minimum number, and shortest duration of disclinations.

[0086] Generally, an acceptable incidence of disclinations includes an acceptable size, an acceptable number, and an acceptable duration of disclinations.

[0087] A person skilled in the art knows how to carry out the method of the invention (in particular to determine the optimal angle or the angle leading to an acceptable disclination) by routine experiments and without inventive effort, as has been demonstrated in the examples. For example, an experimental setup is established in which the angle can be changed or a plurality of autostereoscopic display devices are manufactured, each with a different angle. For each angle, a switching of the autostereoscopic display device is performed and then it is observed whether disclination is formed, in particular whether the size, amount and / or duration of the disclination follows a certain trend towards a certain minimum value.

[0088] Preferably, the angle between the two orientation directions is changed by changing the second liquid crystal orientation direction relative to the rest of the naked eye stereoscopic display device. In other words, changing the angle between the first liquid crystal orientation direction and the second liquid crystal orientation direction in the convex lens device preferably includes: changing the second liquid crystal orientation direction relative to the display panel and relative to the first liquid crystal orientation direction.

[0089] Typically, this involves changing the polarization direction of the linear polarizer by the same degree at the same time, as both directions need to be aligned. Thus, changing the angle between the two liquid crystal alignment directions may further comprise changing the polarization direction of the linear polarizer by the same degree as the second liquid crystal alignment direction is changed, such that the second liquid crystal alignment direction is (still) aligned with the polarization direction of the linear polarizer.

[0090] However, as explained above, it is also possible to position the polarization rotator between the linear polarizer and the second inner surface. This avoids the need to simultaneously change the polarization direction of the linear polarizer, as the polarization rotator can compensate for any differences in polarization direction and liquid crystal alignment direction.

[0091] Another possibility of changing the angle is by changing the first liquid crystal alignment direction relative to the rest of the naked eye stereoscopic display device. In other words, changing the angle between the first liquid crystal alignment direction and the second liquid crystal alignment direction in the convex lens device includes: changing the first liquid crystal alignment direction relative to the display panel and relative to the second liquid crystal alignment direction.

[0092] However, changing the first liquid crystal alignment direction almost inevitably requires changing the orientation of the convex lenses (i.e. their tilt angles) to the same extent, since it is highly preferred that the liquid crystals on the convex lenses be aligned in the direction of elongation of the convex lenses. However, changing the orientation of the convex lenses relative to the orientation of the rest of the device (and thus relative to the pixel array) is undesirable, since only a few combinations of pixel pitch and convex lens tilt angles enable the convex lens liquid crystal unit to function properly, and most combinations will not produce usable imaging. Moreover, the choice of pixel pitch and matching convex lens tilt angle determines the resolution and optimal viewing distance in 3D viewing mode. Furthermore, the range over which the tilt angle can vary is 80° (i.e., 0° to 40° on either side of the vertical direction), so even when a tilt angle outside this range is required, the optimal spiral twist cannot be achieved.

[0093] Therefore, in summary, it is highly preferred that the relative positioning of the convex lens array and the display pixel element array remains unchanged during the change of the angle between the two alignment directions, i.e., the second liquid crystal alignment direction is changed relative to the rest of the naked eye stereoscopic display device. When a polarization rotator is not present, the polarization direction of the linear polarizer needs to be changed accordingly. When a polarization rotator is present, the polarization rotator can overcome any difference between the two directions so that the two directions can be selected independently of each other.

[0094] Since the linear polarizer needs to be integrated into the display panel when the display panel is a liquid crystal display (LCD), changing the polarization direction of the linear polarizer usually requires a novel design of the LCD. However, this is not the case when the display panel is an organic light emitting diode (OLED) display, because OLED does not require a polarizer to produce a display output. Therefore, the polarization direction of the linear polarizer can be freely selected without redesigning the OLED display. Therefore, the display panel in the method of the present invention preferably includes an OLED display rather than an LCD.

[0095] However, the disadvantages of using an LCD can be mitigated when a polarization rotator is used, since this allows the second liquid crystal alignment direction to be selected independently of the polarization direction of the linear polarizer integrated in the LCD.

[0096] The display panel may include a liquid crystal display (LCD) or an organic light emitting diode (OLED) display. When the display panel includes an OLED display, it is preferably also provided with a quarter wave plate. This is because such a wave plate in combination with a linear polarizer in the display panel can serve as an anti-reflection member for the viewer. In the absence of such a member, the OLED display can act as a reflector. The reflection of ambient light caused by such a reflector is usually visible to the viewer of the naked eye stereoscopic display device, and therefore may result in an annoying experience. Due to the reflected extra light, the displayed image will lose contrast and / or blackness.

[0097] The present invention further relates to a naked eye stereoscopic display device capable of being electrically switched between a first view mode and a second view mode, wherein the device has an angle between a first liquid crystal alignment direction and a second liquid crystal alignment direction, the angle resulting in a minimum or acceptable occurrence of disclination after switching from the first view mode to the second view mode. Such a device is typically a device for the method described above.

[0098] The display panel may include a liquid crystal display (LCD) or an organic light emitting diode (OLED) display. For the same reasons described above, the display panel preferably includes an OLED display.

[0099] Disclination occurs in particular when the angle between the first liquid crystal alignment direction and the second liquid crystal alignment direction is 0° or 90°. Disclination also typically occurs when the angle is between 0° and 4° or between 86° and 90°.

[0100] Therefore, in the naked-eye stereoscopic display device of the present invention, the angle between the first liquid crystal alignment direction and the second liquid crystal alignment direction is in the range of 4° to 86°, particularly in the range of 5° to 85°.

[0101] More particularly, it has been found that angles below 45° are effective for reducing disclination. Therefore, the angle is preferably in the range of 5° to 40°, such as in the range of 5° to 35°, 5° to 30°, 5° to 25°, 5° to 20° or 5 to 15°. More preferably in the range of 10° to 25°, such as in the range of 10° to 20°.

[0102] In the naked-eye stereoscopic display device of the present invention, a polarization rotator may be positioned between the linear polarizer and the second inner surface to compensate for any difference between 1) the polarization direction of the linear polarizer and 2) the second liquid crystal alignment direction.

[0103] Typically, the shortest distance between the first inner surface and the second inner surface is in the range of 5.0 μm to 50 μm. This is typically the distance between the apex of the convex lens elements and the (flat) second optically transparent substrate.

[0104] Examples

[0105] 1. Contrast naked eye stereoscopic display device known in the art

[0106] A switchable autostereoscopic display device with a diagonal diameter of 15.6 inches was prepared. The cell gap between the top of the lens (convex lens vertex) and the opposite plate was 10 microns, and the cell gap contained a liquid crystal medium with a refractive index of 0.12. The device had a horizontal display polarization, that is, the display output had a horizontal polarization when it encountered the liquid crystal medium. In addition, the device had a convex lens tilt angle α of 16.7° relative to the vertical axis. s Since the liquid crystal alignment is in the same direction as the tilt angle, the twist angle α of the liquid crystal molecules in the helical configuration is t The angle in the entire cell gap (between the first inner surface and the second inner surface) is 73.3°.

[0107] This is Figure 3 As shown schematically in Figure 3 The foreground plate (5) is shown with the foreground plate (5) aligned horizontally with the horizontal display polarization at an angle α to the vertical. p (α p =90°); and a background plate (4) showing the background, the background square plate (4) is oriented along the tilt direction, forming an angle α with the vertical line s (α s =16.7°). The total torsion angle α between the two plates (4, 5) t Represented by ten steps that fade gradually toward the background plate (α t =73.3°), just like the steps of a spiral staircase.

[0108] The naked-eye stereoscopic display device exhibits very persistent disclinations after switching from the first viewing mode (helical liquid crystal alignment along the helical axis perpendicular to the planar electrodes) to the second viewing mode (liquid crystal alignment perpendicular to the planar electrodes). These disclinations are shown in Figure 5 , where the regular shapes (12) from left to right represent convex lenses, and the curves (13) represent the boundaries between different liquid crystal domains with different liquid crystal orientations (i.e., they represent actual disclinations). To clear the disclinations, a ramp voltage was applied during a period of 20 seconds before the final switching voltage was reached. Significant crosstalk was observed during this period. It was reduced to normal and acceptable values ​​long after this period. In addition, some disclinations were observed to persist even after the final switching voltage was reached.

[0109] 2. The naked-eye stereoscopic display device of the present invention.

[0110] The method of the present invention is to obtain a display device that exhibits less disclination after switching from a first viewing mode to a second viewing mode. To this end, a naked-eye stereoscopic display device is prepared, which has a display polarization angle α relative to the vertical axis. p =32°, and the torsion angle α t= 15.3° (showing a polarization angle of 32° minus a tilt direction angle of 16.7°). In this cell, no disclination occurred during or after switching. Furthermore, no switching delay (ramp voltage) was required and no initial increase in crosstalk was observed.

[0111] This is Figure 4 As shown in FIG. 1 , the angle between the liquid crystal alignment and the display polarization direction is 32°. p , rather than Figure 3 This results in a torsion angle α t is 15.3° instead of Figure 3 73.3°. Figure 3 Compared with the larger torsion angle in t is advantageous because it does not induce disclination.

[0112] Therefore, the naked-eye stereoscopic display device according to the present invention will not substantially undergo disclination after switching, which makes it far superior to the known 2D / 3D switchable naked-eye stereoscopic display device.

Claims

1. A method for reducing disclination in a naked-eye stereoscopic display device (11) capable of electrically switching from a first viewing mode to a second viewing mode, the naked-eye stereoscopic display device (11) comprising: A display panel (1), comprising: An array of display pixel elements for generating a display output; a linear polarizer configured to filter the display output into a well-defined polarization direction; A convex lens device (2) is arranged above a display panel (1), wherein the display panel (1) is electrically switchable to provide a first viewing mode or a second viewing mode, and the convex lens device (2) comprises: a first optically transparent substrate (4) comprising an array of convex lens elements, wherein the convex lens elements have a first inner surface (4a), the first inner surface (4a) having liquid crystal alignment properties including a first liquid crystal alignment direction; A second optically transparent substrate (5) having: an outer surface (5b) facing the linear polarizer and configured to receive a display output; a second inner surface (5a) having a liquid crystal alignment property including a second liquid crystal alignment direction, wherein the second liquid crystal alignment direction is consistent with the polarization direction of the linear polarizer, the first inner surface (4a) and the second inner surface (5a) facing each other; A first plane switching electrode (6) disposed on one side of the first optically transparent substrate (4); A second plane switching electrode (7) disposed on one side of the second optically transparent substrate (5); A liquid crystal medium (8) comprising liquid crystal molecules (9), the liquid crystal medium (8) being sandwiched between two substrates (4, 5) and in contact with a first inner surface (4a) and a second inner surface (5a), wherein In a first viewing mode, the liquid crystal molecules (9) are located in the plane of the two plane switching electrodes (6, 7); and In the second viewing mode, the liquid crystal molecules (9) are oriented perpendicularly to the two plane switching electrodes (6, 7); A component (3) for applying a switching voltage to two planar switching electrodes (6, 7) to achieve switching from a first viewing mode to a second viewing mode; wherein, in a first view mode, the liquid crystal molecules (9) define a helix (10) having a twist, the twist being defined by an angle between a first liquid crystal alignment direction and a second liquid crystal alignment direction; The method comprises changing the angle between a first liquid crystal alignment direction and a second liquid crystal alignment direction in a convex lens device (2), thereby determining an angle causing a minimum disclination or an acceptable disclination after switching from a first viewing mode to a second viewing mode.

2. The method according to claim 1, wherein the minimum disclination or the acceptable disclination occurrence rate comprises at least one of the following: The size of the minimum disclination or acceptable disclination; Minimum disclination or the amount of acceptable disclination; Minimum disclination or duration of acceptable disclination.

3. The method according to claim 1 or 2, wherein the display panel (1) comprises a liquid crystal display (LCD).

4. The method according to claim 1 or 2, wherein the display panel (1) comprises an organic light emitting diode (OLED) display.

5. The method according to claim 4, wherein the display panel (1) comprises an OLED display and a quarter wave plate.

6. The method according to any one of claims 1 to 5, wherein changing the angle between the first liquid crystal alignment direction and the second liquid crystal alignment direction in the convex lens device (2) comprises: The second liquid crystal alignment direction is changed relative to the display panel (1) and relative to the first liquid crystal alignment direction. 7 . The method of claim 6 , wherein changing the angle further comprises changing the polarization direction of the linear polarizer to the same extent as the second liquid crystal alignment direction is changed.

8. A method according to any one of claims 1 to 7, wherein a polarisation rotator is positioned between the linear polariser and the second inner surface (5a), the polarisation rotator compensating for any difference between 1) the polarisation direction of the linear polariser and 2) the second liquid crystal alignment direction.

9. The method according to any one of claims 1 to 8, wherein changing the angle between the first liquid crystal alignment direction and the second liquid crystal alignment direction in the convex lens device (2) comprises: The first liquid crystal alignment direction is changed relative to the display panel (1) and relative to the second liquid crystal alignment direction.

10. A naked-eye stereoscopic display device (11) capable of electrically switching from a first viewing mode to a second viewing mode, the naked-eye stereoscopic display device (11) comprising: A display panel (1), comprising: An array of display pixel elements for generating a display output; a linear polarizer configured to filter the display output into a well-defined polarization direction; A convex lens device (2) is arranged above a display panel, the display panel being electrically switchable to provide a first viewing mode or a second viewing mode, the convex lens device (2) comprising: a first optically transparent substrate (4) comprising an array of convex lens elements, wherein the convex lens elements have a first inner surface (4a), the first inner surface (4a) having liquid crystal alignment properties including a first liquid crystal alignment direction; A second optically transparent substrate (5) having: an outer surface (5b) facing the linear polarizer and configured to receive a display output; a second inner surface (5a) having a liquid crystal alignment property including a second liquid crystal alignment direction, the second liquid crystal alignment direction being consistent with the polarization direction of the linear polarizer, the first inner surface (4a) and the second inner surface (5a) facing each other; A first plane switching electrode (6) disposed on one side of the first optically transparent substrate (4); A second plane switching electrode (7) disposed on one side of the second optically transparent substrate (5); A liquid crystal medium (8) comprising liquid crystal molecules (9), the liquid crystal medium (8) being sandwiched between two substrates (4, 5) and in contact with a first inner surface (4a) and a second inner surface (5a), wherein In a first viewing mode, the liquid crystal molecules (9) are located in the plane of the two plane switching electrodes (6, 7); and In the second viewing mode, the liquid crystal molecules (9) are oriented perpendicularly to the two plane switching electrodes (6, 7); A component (3) for applying a switching voltage to two planar switching electrodes (6, 7) to achieve switching from a first viewing mode to a second viewing mode; in In a first view mode, the liquid crystal molecules (9) define a helix (10) having a twist, the twist being defined by an angle between the first liquid crystal alignment direction and the second liquid crystal alignment direction; An angle between the first liquid crystal alignment direction and the second liquid crystal alignment direction is in a range of 4° to 86°.

11. The naked-eye stereoscopic display device (11) according to claim 10, wherein the display panel (1) comprises a liquid crystal display (LCD).

12. The naked-eye stereoscopic display device (11) according to claim 10, wherein the display panel (1) comprises an organic light emitting diode (OLED) display.

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

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

15. The naked-eye stereoscopic display device (11) according to any one of claims 10 to 14, wherein a polarization rotator is positioned between the linear polarizer and the second inner surface (5a), and the polarization rotator compensates for any difference in 1) the polarization direction of the linear polarizer and 2) the second liquid crystal alignment direction.

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

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