Reducing moire in naked eye stereoscopic display device

Abstract

The invention relates to a two-dimensional (2D) / three-dimensional (3D) switchable naked eye three-dimensional display device, which is optimized so that the naked eye three-dimensional display device shows reduced moire patterns. This is accomplished by providing a nanorelief structure on a surface in contact with the liquid crystal switching medium. This results in scattering, thereby reducing moire. The amount of scattering may be influenced by varying the electric field applied to the liquid crystal medium. The invention also relates to a method for reducing moire patterns in the naked eye stereoscopic display device and a method for manufacturing the naked eye stereoscopic display device.

Description

Technical Field

[0001] The present invention relates to an autostereoscopic display device exhibiting reduced moire, a method of reducing moire in an autostereoscopic display device, and a method of manufacturing an autostereoscopic display device exhibiting reduced moire. Background Art

[0002] Displays capable of electrically switching between two-dimensional and three-dimensional viewing modes, often referred to as 2D / 3D switchable autostereoscopic displays, have attracted a great deal of attention over the past two decades. A common approach is to arrange pixel arrays (display pixel elements) with a lens device consisting of an array of semi-cylindrical microlenses (lenticulars) adjacent to a liquid crystal medium that can be switched between two liquid crystal orientations under the action of an electric field. In the first orientation, the director of the liquid crystal medium is in the plane of the display; in the second orientation, the director of the liquid crystal medium is perpendicular to the plane of the display.

[0003] In this arrangement, each lenticular lens is associated with a set of at least two columns (sub) of pixels that extend parallel to the lens or at an angle (tilt) to it. The pixel output through the lenticular device is affected by the optical properties of the lenticular lens and the liquid crystal medium. The refractive index of the lenticular 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 liquid crystal director, and the second refractive index corresponds to light polarized perpendicular to the director. When the pixel output moves substantially perpendicular to the display plane, it "sees" the first or second refractive index. In the first view mode, the liquid crystal medium is in the first orientation. Its refractive index matches that of the lenticular lens, which causes the lenticular lens to lose its focusing effect and makes the lenticular device appear as a transparent and flat optical panel. This constitutes a two-dimensional view mode for naked-eye stereoscopic display. In the second view mode, the liquid crystal medium is in the second liquid crystal orientation. The refractive indices do not match, which causes each lenticular lens to exhibit a focusing effect. This makes it possible to direct the output of different pixel columns to different spatial locations in front of the autostereoscopic display, thereby allowing the viewer to perceive a three-dimensional image composed of a left image and a right image. This forms a three-dimensional viewing mode of the autostereoscopic display.

[0004] One problem with many 2D / 3D switchable autostereoscopic displays is that the viewer perceives a moiré pattern due to the superposition of the pattern of the pixel array and the pattern of the lenticular lens array. Such a pattern is often distracting to the viewer. Furthermore, the moiré pattern makes the screen itself visible, as are reflections, for example. This breaks the illusion of a "free-floating" three-dimensional image in the space in front of and behind the screen.

[0005] To date, many measures have been taken to reduce or even completely eliminate moiré patterns in such displays. For example, the pixels that contribute most to moiré can be identified and their pixel output modified in a specific way. However, this has undesirable side effects such as reduced resolution and reduced display intensity. It also requires valuable processor capacity. Other solutions involve the application of specific pixel shapes and pixel arrangements in combination with specific lenticular lens tilt angles. However, this limits the design opportunities for autostereoscopic display devices and makes the manufacturing process more critical, as tilt deviations as small as a fraction of a degree can already cause moiré. Summary of the invention

[0006] Therefore, an object of the present invention is to find a solution to the appearance of moiré patterns, in particular a solution that does not exhibit one or more of the above-mentioned side effects. Another object is to provide a solution that is simpler than the solutions known in the art. More generally, an object of the present invention is to improve the viewing experience of viewers of naked-eye stereoscopic displays.

[0007] It has now been found that one or more of these objects can be achieved by certain modifications of the surface adjacent to the liquid crystal medium in a switchable autostereoscopic display.

[0008] Therefore, the present invention relates to a naked-eye stereoscopic display device (10) which can be electrically switched from a first viewing mode to a second viewing mode, the naked-eye stereoscopic display device (10) comprising

[0009] - a display panel (1) having an array of display pixel elements for generating a display output;

[0010] - a cylindrical lens device (2) arranged on the display panel (1), the cylindrical lens device (2) being electrically switchable to provide the first viewing mode or the second viewing mode, wherein, in one of the two viewing modes, the cylindrical lens device (2) comprises a lens area, the lens area being capable of directing display outputs from different display pixel elements to different spatial positions within the field of view of the naked-eye stereoscopic display device (10) to allow display of a naked-eye stereoscopic image composed of a left image and a right image, the cylindrical lens device (2) comprising

[0011] o a first optically transparent substrate (4), comprising an array of lenticular lens elements disposed on the first optically transparent substrate (4), wherein the lenticular lens elements have a first surface (4a) with liquid crystal alignment properties;

[0012] o a second optically transparent substrate (5), the second optically transparent substrate (5) having a second surface (5a) with liquid crystal alignment properties, the first surface (4a) and the second surface (5a) being opposite to each other;

[0013] o a first plane switching electrode (6), which is arranged on one side of the first optically transparent substrate (4);

[0014] o a second plane switching electrode (7), which is arranged on one side of the second optically transparent substrate (5);

[0015] o a liquid crystal medium (8) comprising liquid crystal molecules (9), said liquid crystal medium (8) being sandwiched between two substrates (4, 5), wherein it is in contact with said first surface (4a) and said second surface (5a), wherein

[0016] 1. In the first viewing mode, the liquid crystal molecules (9) are located in the plane of the in-plane switching electrodes (6, 7); and

[0017] 2. In the second viewing mode, the liquid crystal molecules (9) are oriented perpendicular to the two plane switching electrodes (6, 7);

[0018] - means (3) for applying a switching voltage between the two in-plane switching electrodes (6, 7) to achieve switching from a first viewing mode to a second viewing mode;

[0019] The first surface (4a) and / or the second surface (5a) comprises a surface relief structure (11) having a surface relief size, which can cause scattering of display output when liquid crystal molecules (9) contained in the surface relief structure (11) have an orientation whose refractive index is different from the refractive index of the surface relief structure (11).

[0020] The present invention also relates to a method for reducing moiré in a naked-eye stereoscopic display device, wherein the naked-eye stereoscopic display device is the naked-eye stereoscopic display device (10) as described above, and the method comprises modifying a switching voltage to reduce the moiré.

[0021] The present invention also relates to a method for manufacturing a naked-eye stereoscopic display device, the method comprising:

[0022] - providing a naked eye stereoscopic display device as described above; then

[0023] - Execute the above method. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The naked eye stereoscopic display device (10) in a first viewing mode is schematically shown.

[0025] Figure 2The naked eye stereoscopic display device (10) in the second viewing mode is schematically shown.

[0026] Figure 3 A cross section of a nanorelief structure (11) superimposed on the surface of a first optically transparent substrate (4) is shown.

[0027] Figure 4 A cross section of a nano-relief structure (11) superimposed on the surface of a second optically transparent substrate (5) is shown.

[0028] Figure 5 A graph (20) showing the height of the nano-relief structure (11) as a function of the direction on the surface is shown.

[0029] Figure 6 Six photographs are shown of light transmission through a liquid crystal cell comprising a unidirectional nanorelief structure, wherein different voltages are applied across the cell according to the example.

[0030] Figure 7 An experimental setup according to an example is schematically shown. DETAILED DESCRIPTION

[0031] The elements in the figures are illustrated for simplicity and clarity and are not necessarily drawn to scale. For example, the sizes of certain elements in the figures may be exaggerated relative to other elements to help improve understanding of various exemplary embodiments of the present invention. For example, the relative sizes of different components of the naked-eye stereoscopic display device cannot be derived from the figures. For example, this involves the size of the nano-relief structure relative to the cylindrical lens elements and the schematic liquid crystal molecules. It is also not possible to deduce how the different sizes of the nano-relief structure itself are related to each other (e.g., the height of the ridge, the width of the ridge, and the width of the valley).

[0032] Furthermore, the terms "first", "second", and the like in the description and the claims, if any, are generally used to distinguish between similar elements and not necessarily to describe a sequential or chronological order.

[0033] In the context of the present invention, the term "viewer" refers to a person who is able to consume (especially watch) content presented by a naked-eye stereoscopic display device. Throughout the text, references to the viewer will be represented by masculine terms such as "he", "him" or "his". This is only for clarity and brevity, and it is understood that feminine terms such as "she" and "her" are equally applicable.

[0034] In the context of the present invention, the term "moiré" refers to a pattern perceived by a viewer as a superposition of two real patterns that are slightly displaced, slightly rotated, and / or have slightly different pitches ("moiré pattern"). In addition, moiré may occur when the pitch of one pattern is nearly (but not exactly) a multiple of an integer (2, 3, 4, etc.) of the pitch of the other pattern. The moiré that is reduced or overcome in the present invention generally involves the superposition of the pattern of the pixel array and the pattern of the lenticular lens array.

[0035] It will be appreciated that the liquid crystal medium is a birefringent material having a first refractive index for linearly polarized light propagating along the director of the liquid crystal medium and a second refractive index for linearly polarized light propagating 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 expressly stated otherwise, this refers to the refractive index of the liquid crystal medium in the direction perpendicular to the planar switching electrodes, i.e. the direction in which the display output (i.e. linearly polarized light) propagates. The refractive index may refer to the first refractive index or the second refractive index defined above, depending on the electric field applied to the liquid crystal medium.

[0036] In the naked eye stereoscopic display device of the present invention, the liquid crystal medium is present between two opposite surfaces, i.e. it is in contact with two surfaces. These relate to a first surface, which is the surface of a cylindrical lens element arranged on a first optically transparent substrate, and a second surface, which is the surface of a second optically transparent substrate. Both surfaces have liquid crystal alignment properties. The first surface is cylindrical lens-shaped, while the second surface can in principle be of any shape. However, usually the second surface is a plane or cylindrical lens-shaped surface. In the latter case, there are two opposite cylindrical lens surfaces.

[0037] The liquid crystal medium comprises liquid crystal molecules. Two plane switching electrodes are located on both sides of the liquid crystal medium, so that the two plane switching electrodes can apply an electric field to the liquid crystal medium. The liquid crystal molecules can be oriented in the plane of the plane switching electrodes under the influence of the surface alignment properties; or oriented in the plane normal direction of the plane switching electrodes under the influence of the voltage applied between the two plane switching electrodes. Each of these two different directions will produce a different view mode.

[0038] The two view modes are as follows Figure 1 and Figure 2As shown, the figure shows a cross-sectional view of a liquid crystal unit of a naked-eye stereoscopic display device (10) of the present invention. The naked-eye stereoscopic display device includes a cylindrical lens device (2), which is arranged on a display panel (1), and the display panel (1) has a display pixel element array for generating a display output. The cylindrical lens device (2) includes a liquid crystal medium (8), and the liquid crystal medium (8) includes liquid crystal molecules (9). The liquid crystal medium (8) is sandwiched between two optically transparent substrates (4, 5), and the two optically transparent substrates (4, 5) are sandwiched between two planar switching electrodes (6, 7). The liquid crystal medium (8) is adjacent to the first surface (4a) and the second surface (5a) of the two respective optically transparent substrates (4, 5). The cylindrical lens device (2) can be electrically switched to provide a first view mode or a second view mode. Switching is performed by applying a switching voltage to the two planar switching electrodes (6, 7), and a device (3) is provided for this purpose. Figure 1 The elongated direction of the liquid crystal molecules (9) is perpendicular to the plane of the display pattern. Figure 2 The elongated direction of the liquid crystal molecules (9) is parallel to the plane of the display image.

[0039] In the absence of an electrical potential, the molecules are oriented in the plane of the planar switching electrode and according to the liquid crystal alignment properties of the first and second surfaces, thereby defining a first view mode. When a sufficiently strong electrical potential ("switching voltage") is applied, they switch to an orientation consistent with a corresponding electric field, which is perpendicular to the plane of the planar switching electrode, thereby defining a second view mode. The switching voltage is therefore the voltage at which the naked-eye stereoscopic display device changes to and maintains its second view mode. There is usually a threshold voltage, above which a change to the second view mode occurs. The switching voltage is therefore in principle any voltage above this threshold voltage.

[0040] In a naked-eye stereoscopic display device that can switch between two viewing modes by electrical switching, it is possible to switch from one liquid crystal orientation to another. This is achieved by changing the electric field to which the liquid crystal medium is subjected. The main part of the liquid crystal medium follows the electric field and switches, and the entire medium changes uniformly. However, this is not the case at the interface between the liquid crystal medium and the surface having liquid crystal alignment characteristics. Here, the liquid crystal molecules are anchored to the surface that aligns them under the flux of the anchoring force. They have no substantial orientation freedom, especially the first layer of liquid crystal molecules has no substantial orientation freedom. Therefore, when the liquid crystal molecules are aligned on the surface and the plane of the surface, they are less likely to switch to a direction perpendicular to the surface relative to the molecules in the main part of the liquid crystal medium. This is due to the anchoring force, and causes most of the liquid crystal molecules (i.e., molecules farther from the surface) to have switched, while a small layer bordering the surface has not switched. In the context of the present invention, this layer is called a "boundary layer". It is estimated that there is no obvious transition between the boundary layer and the main part, and the adjacent liquid crystal molecules will gradually adapt their orientation to the orientation of the main part.

[0041] The presence of the boundary layer makes the refractive index of the liquid crystal medium near the surface different from the refractive index of the bulk part. This means that a situation can be created in which one part of the liquid crystal medium has a refractive index that matches the refractive index of the material surrounding the liquid crystal medium (typically the lenticular lens elements and the second optically transparent substrate); and in which another part has a mismatched refractive index. This boils down to two cases: 1) the refractive index of the boundary layer matches the refractive index of the surrounding material, while the refractive index of the bulk part is different; 2) the refractive index of the bulk part matches the refractive index of the surrounding material, while the refractive index of the boundary layer is different.

[0042] The effect of the first case is that the display output of a display pixel element (i.e., light) that passes through the surrounding material "experiences" the surrounding material as being slightly thicker than it actually is. This is because light travels a longer distance in a medium with a particular refractive index; in other words, the light "does not see" the difference between the surrounding material and the boundary layer in terms of refraction.

[0043] The present invention utilizes the first situation to reduce moiré.

[0044] First, a nano-relief structure is introduced to the surface of the surrounding material (or a portion of it). This structure scatters the pixel output, thereby reducing moiré.

[0045] Secondly, the degree of scattering can be controlled by increasing the thickness of the boundary layer. When the boundary layer is thin, the nanorelief structure is highly "visible" to the pixel output. The thicker the boundary layer, the more the nanorelief structure is "submerged" by it and the less "visible" it is to the pixel output. This is due to the effects described above, especially the effects occurring in case 1). Here, the structural features in the nanorelief structure are surrounded by a medium with the same refractive index, which effectively deprives them of their light scattering properties.

[0046] The thickness of the boundary layer can be adjusted by varying the switching voltage; the higher the voltage (i.e., the stronger the electric field), the greater the force applied, which helps to overcome the anchoring forces of the surface and change the orientation of the liquid crystal molecules that are close to the surface and have been aligned. Therefore, by varying the switching voltage, the severity of the scattering can be influenced.

[0047] The inventors have now discovered that the appearance of moiré patterns can be reduced by applying an appropriate electric field.

[0048] Consider further that, theoretically, favorable scattering may increase crosstalk as a side effect. Crosstalk refers to the phenomenon in naked-eye stereoscopic displays whereby (a small portion of) light from a display pixel element, which was originally intended for the left eye, enters the right eye, and vice versa. It will be explained below how the present invention solves the eventual occurrence of crosstalk caused by scattering.

[0049] As described above, the thickness of the boundary layer can be adjusted by changing the switching voltage. This changes the degree of scattering of the pixel output, thereby affecting the moiré pattern. Therefore, according to the present invention, moiré can be reduced by appropriately adjusting the voltage between the two planar switching electrodes. Therefore, an important element of the naked eye stereoscopic display device of the present invention is a device for applying this switching voltage on the two planar switching electrodes.

[0050] In one embodiment, the device (3) is configured to apply a switching voltage that allows the nano-relief structure to cause a reduction in scattering and moiré of the display output. In this embodiment, the device sets a switching voltage that has been shown to cause less moiré than other switching voltages and / or where the best results have been achieved in terms of moiré and image quality. This is typically a factory setting that remains unchanged throughout the life of the display device.

[0051] In another embodiment, the device is capable of applying at least two switching voltages of different amplitudes. In this embodiment, a switching voltage that minimizes moiré can be selected. Therefore, through this embodiment, the setting of the naked eye stereoscopic display device can be optimized.

[0052] This can be done in the factory as part of manufacturing the autostereoscopic display device. Since deviations as small as a fraction of a degree can already cause moiré, the manufacturing process usually has very small tolerances. When moiré can be compensated after manufacturing, these tolerances can be relaxed, which has certain advantages.

[0053] In addition, during the manufacturing process, the parameters of the cylindrical lens device (such as spacing, inclination) and the nano-relief structure parameters can first be selected to be approximately correct. Secondly, after assembling the naked-eye stereoscopic display device with different components, fine-tuning can be performed for each product or each product series by setting an appropriate switching voltage. For conventional naked-eye stereoscopic display devices, multiple iteration cycles in design and manufacturing are necessary, while the naked-eye stereoscopic display device using the present invention can skip these iteration cycles.

[0054] The setting optimization of the naked eye stereoscopic display device can also be performed at the discretion of the viewer of the device, usually when he is disturbed by the moiré pattern. Therefore, in one embodiment, the naked eye stereoscopic display device of the present invention is designed to allow the viewer of the naked eye stereoscopic display device to reduce the moiré by adjusting the switching voltage.

[0055] When the means for applying the switching voltage is capable of applying at least two switching voltages of different amplitudes, their number is usually greater than two, such as at least three, at least four, at least five, at least seven or at least ten. It may also be at least 15, at least 25 or at least 50. It may also be continuously variable.

[0056] The nano-relief structure is a surface relief of the surface of the cylindrical lens element of the first optically transparent substrate and / or the surface of the second optically transparent substrate. This means that the nano-relief structure is a structure superimposed on the corresponding surface. Since the surface of the first optically transparent substrate is a cylindrical lens surface (i.e., the surface of the cylindrical lens element), the nano-relief structure is superimposed on the cylindrical lens surface. Similarly, since the surface of the second optically transparent substrate is a plane, the nano-relief structure is superimposed on the plane. This is in Figure 3 and Figure 4 It is explained in Figure 3 and Figure 4 An enlarged view showing a part of a cross-sectional view of a liquid crystal unit of a naked-eye stereoscopic display device (10) of the present invention ( Figure 1 and Figure 2 A larger portion of the unit is shown, but with less detail). Figure 3 and Figure 4 A cross section of the nano-relief structure (11) on each optically transparent substrate (4, 5) is shown.

[0057] Figure 3A cross section of a nano-relief structure (11) superimposed on a first optically transparent substrate (4) is shown. This is a cross section of a cylindrical lens element (perpendicular to its elongation direction) of the first optically transparent substrate (4). Along the curve of the cylindrical lens cross section are a large number of adjacent valleys and ridges (also viewed in a cross section perpendicular to their elongation direction). The first surface (4a) of the first optically transparent substrate (4) is formed by valleys and ridges.

[0058] Figure 4 A cross section of a nano-relief structure (11) superimposed on a second optically transparent substrate (5) is shown. Along the straight cross section of the second optically transparent substrate (5) are a large number of adjacent valleys and ridges (the cross section is observed perpendicular to their elongated direction). The second surface (5a) of the second optically transparent substrate (5) is formed by valleys and ridges.

[0059] Since the liquid crystal medium (8) is sandwiched between the two optically transparent substrates (4, 5), wherein the liquid crystal medium (8) is in contact with the surfaces (4a, 5a) of the two optically transparent substrates (4, 5), the nano-relief structure is completely sunken in the liquid crystal medium (8). This means that the liquid crystal molecules (9) completely fill the valleys of the nano-relief structure, so that the surfaces of the valleys and ridges are located at the interface of the corresponding optically transparent substrate (4 or 5) and the liquid crystal medium (8).

[0060] The nanorelief structure has a surface relief dimension that causes scattering of the display output when the nanorelief structure is illuminated by the display output, for example when the display output passes through it (and through the corresponding optically transparent substrate of which the nanorelief structure forms a part). This design requirement relies on the following situation: when the liquid crystal molecules are oriented perpendicular to the two plane switching electrodes, the nanorelief structure (or a part of it) has an interface with a liquid crystal medium whose refractive index does not match the refractive index of the nanorelief structure (and therefore the refractive index of the corresponding optically transparent substrate to which it belongs). This requires that the liquid crystal molecules with such a perpendicular orientation are contained in the nanorelief structure, that is, they are present in the valleys between the ridges of the nanorelief structure. In other words, this involves a situation in which the boundary layer does not completely cover the nanorelief structure; therefore, at least a part of the nanorelief structure (especially its ridges) resides in the main part of the liquid crystal medium, in which the liquid crystal molecules are oriented perpendicular to the two plane switching electrodes. In this way, the nanorelief structure becomes "visible" to the display output, thereby causing scattering of the display output.

[0061] This is Figure 5, which shows a graph (20) of the height of the nanorelief structure (11) as a function of the surface direction. On the left, a thick boundary layer (12) is superimposed on the graph (20), while on the right, a thin boundary layer (13) is superimposed on the graph (20). The liquid crystal molecules (14) in the thick boundary layer (12) are only present "above" the nanorelief structure, while the liquid crystal molecules (15) in the thin boundary layer (13) are also present between the peaks (or ridges) of the nanorelief structure (11).

[0062] In order to actually achieve the desired scattering, the nano-relief structure needs to be of appropriate size so as to show the scattering of the output. A person skilled in the art knows how to create and implement such a nano-relief structure by routine experiments without inventive effort.

[0063] For example, surface features responsible for scattering typically have at least one dimension in the range of 1 nm to 1.000 nm, preferably in the range of 1 nm to 500 nm.

[0064] Typically, the height of the nano-relief structures (and surface features) is 1.000 nm or less, preferably 500 nm or less. Larger relief heights require thicker boundary layers on the lens to achieve a certain degree of scattering. Since this thick boundary layer significantly increases the thickness of the lens, it actually causes lens deformation. Since lens deformation is preferably minimized (because it can cause loss of field of view, especially crosstalk), it is preferred to limit the height of the nano-relief structures (and surface features).

[0065] The nano-relief structure is preferably a non-periodic structure and / or does not have a regular structure, as this may result in a moiré pattern.

[0066] Preferably, the nano-relief structure comprises substantially parallel grooves. These grooves, when oriented horizontally, have the advantage of minimizing scattering in the horizontal direction. This in turn minimizes crosstalk caused by scattering, because crosstalk is caused by a deviation of light in the horizontal direction. In a naked-eye stereoscopic display, crosstalk refers to a phenomenon in which (a small portion of) light from a display pixel element, originally designed for the left eye, reaches the right eye, and vice versa - a horizontal deviation. Crosstalk affects the quality of the 3D view experience. The characteristic of a horizontal groove is that it scatters light mainly in the vertical direction; crosstalk is largely insensitive to scattering in the vertical direction. Therefore, when grooves are present, they are preferably horizontal (i.e., extending between the left and right in the viewer's field of view). This means that the grooves are preferably parallel to the lateral direction in which the left and right images are displaced, i.e., the left and right directions set by the lateral displacement of the left and right images generated by the naked-eye stereoscopic display device. The grooves may also extend in a direction that deviates from the lateral direction by less than 30° or less than 20°, preferably less than 10° or less than 5°.

[0067] Since autostereoscopic display devices are usually rectangular and are usually viewed in a landscape orientation (rather than a portrait orientation), the groove direction usually corresponds to the elongated direction of the device. This direction ideally corresponds to the viewer's interpupillary direction, i.e., the direction of an imaginary line connecting the two eyes. In practice, the viewer will move and rotate relative to the display device, causing the direction to change over time.

[0068] Typically, the height of the groove is 1.000 nm or less. The height of the groove is preferably 500 nm or less, because a greater height will cause more lens deformation (see explanation above). The width of the groove is typically in the range of 50 nm to 5.000 nm. The length of the groove is typically at least 10 μm. For example, the length of the groove is in the range of 10 μm to 10.000 μm or in the range of 20 μm to 2.000 μm.

[0069] The grooves are preferably non-periodic and / or do not have a regular structure, as this may produce a moiré pattern. The length of the grooves is in principle not limited, but it is contemplated that a plurality of very long (and parallel) grooves may also produce a moiré effect.

[0070] When the nano-relief structures are in the form of grooves, there are two surface properties defined by their directions: the grooves and the liquid crystal alignment. In a preferred embodiment, the two directions are the same or substantially the same. Therefore, in the naked eye stereoscopic display device according to the present invention, the liquid crystal alignment property includes the property of aligning the liquid crystal molecules along a direction substantially parallel to the grooves.

[0071] However, a nanorelief structure may also include surface features that have no particular orientation preference. For example, a nanorelief structure includes randomly oriented surface features having a length, width, and height, wherein

[0072] - Width and length are independent of each other in the range of 50nm to 5.000nm;

[0073] -Height in the range of 1nm to 500nm;

[0074] - The length shall not exceed 4 times the width.

[0075] It is generally preferred that the nano-relief structure is designed in such a way that more than 50%, preferably more than 80%, and more preferably more than 90% of the scattered display output is scattered in a direction perpendicular to the lateral direction of the displacement of the left and right images, i.e., the left and right directions of the lateral displacement settings of the left and right images configured by the naked eye stereoscopic display device to generate. The direction may also deviate from this lateral direction by less than 30°, or less than 20°, or less than 10°, or less than 5°. This direction is ideally perpendicular to the viewer's interpupillary direction, i.e., the direction of the imaginary line connecting the two eyes.

[0076] Since autostereoscopic display devices are typically rectangular and are usually viewed in a landscape orientation (rather than a portrait orientation), the scattering direction typically corresponds to the short direction of the device.

[0077] The nano-relief structure exists between one or both surfaces of the liquid crystal medium. Therefore, in the naked eye stereoscopic display device according to the present invention,

[0078] - the nano-relief structure is present on the first surface but not on the second surface; or

[0079] - the nano-relief structure is present on the second surface but not on the first surface; or

[0080] - The nano-relief structure is present on the first surface and the second surface.

[0081] The present invention also relates to a method for reducing moiré in a naked-eye stereoscopic display device, wherein the naked-eye stereoscopic display device is the naked-eye stereoscopic display device as described above, and the method comprises modifying a switching voltage to reduce the moiré.

[0082] The method basically utilizes the naked-eye stereoscopic display device of the present invention as described above, including all the embodiments as described above.

[0083] The method of the invention comprises optimizing the switching voltage to reduce moiré. This generally comprises modifying the switching voltage, in particular increasing the switching voltage. This can be performed during the manufacturing process of the naked-eye stereoscopic display device (generally after the main components are assembled) or by the viewer. Since moiré is difficult to capture with a camera (since this may even introduce moiré in the camera recording), the optimization is preferably performed manually, i.e. by a person.

[0084] In one embodiment, optimizing the switching voltage includes applying the following sequence of steps:

[0085] 1) Increase the voltage between the two planar switching electrodes by a certain amplitude; then

[0086] 2) Observe the naked eye stereoscopic display device and check whether a moiré pattern can be observed; then

[0087] 3) If moiré patterns are observable, decide whether to reduce the moiré patterns; and then

[0088] 4) If moiré reduction is required, repeat method steps 1) to 4) until no moiré pattern is observed; or until an acceptable moiré pattern is observed.

[0089] Preferably, in this method, the eventual presence of crosstalk is also taken into account. This can be achieved by a method step in which it is checked whether crosstalk is present and it is decided whether it needs to be reduced.

[0090] As described above, as a factory setting, an appropriate voltage for reducing moiré can be incorporated into the naked-eye stereoscopic display device of the present invention. Therefore, the method of the present invention can also be used when manufacturing the naked-eye stereoscopic display device of the present invention. Therefore, the present invention also relates to a method for manufacturing a naked-eye stereoscopic display device, the method comprising

[0091] -Providing a naked-eye stereoscopic display device as described above;

[0092] - Execute the above method.

[0093] Example

[0094] A non-periodic nano-relief structure is formed in a flat copper sheet using unidirectional mechanical grinding. The unidirectional nano-relief structure consists of Figure 5 The structure (11) in the diagram (20) of FIG. A photopolymerized resin is poured onto the copper nano-relief structure, an ITO glass panel is placed on top, and then UV-cured. After separation from the copper sheet, a glass panel with cured resin is obtained, wherein a unidirectional nano-relief structure exists on the cured resin.

[0095] A rubbed polyimide coated glass panel is provided, wherein an ITO glass panel is sandwiched between the polyimide and the glass.

[0096] Then, a twisted nematic liquid crystal cell was prepared using a nano-relief glass panel and a rubbed polyimide-coated glass panel, where the nano-relief structure faced the rubbed polyimide side. The twisted nematic liquid crystal was filled into the cell by capillary action and sealed with glue. The wires were connected and then a curing step was performed at high temperature.

[0097] Then set up, such as Figure 7 The light (21) from the laser pointer (22) is allowed to be transmitted through the liquid crystal cell (23), and the emitted light (24) is projected onto a piece of paper (25), making it visible to a viewer (26). The unidirectional nano-relief structure is perpendicular to Figure 7plane. There is a means for applying a switching voltage (27) capable of applying a continuously variable voltage to the liquid crystal cell (23). A voltmeter (not shown) indicating the applied voltage is also visible to the viewer (26). Depending on the voltage, part of the emitted light (24) is scattered light 24a, which is also projected onto the paper (25).

[0098] An electric field is applied to the liquid crystal cell by applying a voltage that increases slowly from 0 to 30 V. Until about 11 V, the projection of the outgoing light (24) on the paper (25) is clear, which means that the laser light (21) is not refracted / scattered. At around 11 V, the laser light (21) starts to refract perpendicularly to the unidirectional nano-relief structure. This effect increases up to about 18 V, after which it remains constant. Figure 6 The six photographs show different stages during the voltage increase. The foreground of each photograph shows the actual applied voltage, and the background is the paper (25).

Claims

1. A naked-eye stereoscopic display device (10), which can be electrically switched from a first viewing mode to a second viewing mode, the naked-eye stereoscopic display device (10) comprising - a display panel (1) having an array of display pixel elements for generating a display output; - a cylindrical lens device (2) arranged on the display panel (1), the cylindrical lens device (2) being capable of being electrically switched to provide the first viewing mode or the second viewing mode, wherein, in one of the two viewing modes, the cylindrical lens device (2) comprises a cylindrical lens area, the lens area being capable of directing display outputs from different display pixel elements to different spatial positions within the field of view of the naked-eye stereoscopic display device (10) to allow display of a naked-eye stereoscopic image composed of a left image and a right image, the cylindrical lens device (2) comprising o a first optically transparent substrate (4) comprising an array of lenticular lens elements, wherein the lenticular lens elements have a first surface (4a) having liquid crystal alignment properties; o a second optically transparent substrate (5) having a second surface (5a), the second surface (5a) having liquid crystal alignment properties, the first surface (4a) and the second surface (5a) being opposite to each other; o a first plane switching electrode (6), which is arranged on one side of the first optically transparent substrate (4); o a second plane switching electrode (7), which is arranged on one side of the second optically transparent substrate (5); o a liquid crystal medium (8) comprising liquid crystal molecules (9), said liquid crystal medium (8) being sandwiched between two optically transparent substrates (4, 5), wherein said liquid crystal medium (8) is in contact with said first surface (4a) and said second surface (5a), wherein 1. In the first viewing mode, the liquid crystal molecules (9) are located in the plane of the in-plane switching electrodes (6, 7); and 2. In the second viewing mode, the liquid crystal molecules (9) are oriented perpendicular to the two plane switching electrodes (6, 7); - means (3) for applying a switching voltage between the two in-plane switching electrodes (6, 7) to achieve switching from a first viewing mode to a second viewing mode; in, Nano-relief structures exist at the following locations (11) - on the first surface (4a) of the cylindrical lens elements of the first optically transparent substrate (4); and / or - on the second surface (5a) of the second optically transparent substrate (5); Wherein, the nano-relief structure (11) - comprising valleys between the ridges, wherein the valleys are filled with liquid crystal molecules (9) of a liquid crystal medium (8); - when the nano-relief structure (11) is illuminated by a display output, and when the liquid crystal molecules (9) contained in the valleys of the nano-relief structure (11) are oriented such that the refractive index of the liquid crystal medium (8) in the valleys is different from the refractive index of the nano-relief structure (11), the display output is scattered.

2. The naked eye stereoscopic display device (10) according to claim 1, wherein: The means (3) for applying a switching voltage is designed to apply a switching voltage that allows the nano-relief structure to cause a reduction in scattering and moiré of the display output.

3. The naked-eye stereoscopic display device (10) according to claim 1 or 2, wherein the device (3) for applying a switching voltage is capable of applying at least two switching voltages of different amplitudes.

4. The naked-eye stereoscopic display device (10) according to any one of claims 1 to 3, which is designed to allow a viewer of the naked-eye stereoscopic display device (10) to reduce moiré by adjusting a switching voltage.

5. The naked eye stereoscopic display device (10) according to any one of claims 1 to 4, wherein: The nano-relief structure comprises substantially parallel grooves, the direction of the grooves being parallel to a lateral direction on which a left image and a right image are displaced, the left image and the right image being generated by the naked-eye stereoscopic display device (10), or the direction of the grooves deviating from the lateral direction by no more than 10°.

6. The naked eye stereoscopic display device (10) according to claim 5, wherein the height of the groove is in the range of 1 nm to 1.000 nm and the width thereof is in the range of 50 nm to 5.000 nm.

7. The naked-eye stereoscopic display device (10) according to claim 5 or 6, wherein the liquid crystal alignment property comprises a property of aligning liquid crystal molecules in a direction consistent with a direction of the substantially parallel grooves.

8. The naked-eye stereoscopic display device (10) according to any one of claims 1 to 4, wherein the nano-relief structure comprises surface features having a random orientation, the surface features having a length, a width and a height, wherein - width and length are independent of each other in the range of 50nm to 5.000nm; and - a height in the range of 1 nm to 500 nm; and - The length shall not exceed 4 times the width.

9. A naked-eye stereoscopic display device (10) according to any one of claims 1 to 8, wherein the nano-relief structure is designed in such a way that more than 50%, preferably more than 80%, of the scattered display output is scattered in a direction perpendicular to a lateral direction in which a left image and a right image are displaced, or in a direction that deviates from the lateral direction by no more than 10°, and the left image and the right image are configured to be generated by the naked-eye stereoscopic display device (10).

10. The naked eye stereoscopic display device (10) according to any one of claims 1 to 9, wherein: - the nano-relief structure is present on the first surface (4a) but not on the second surface (5a); or - the nano-relief structure is present on the second surface (5a) but not on the first surface (4a); or The nano-relief structure is present on the first surface (4a) and the second surface (5a).

11. The naked eye stereoscopic display device (10) according to any one of claims 1 to 10, wherein: The nano-relief structure is a non-periodic structure and / or has no regular structure.

12. A method for reducing moiré in a naked-eye stereoscopic display device, wherein: The naked-eye stereoscopic display device is a naked-eye stereoscopic display device (10) as defined in any one of claims 1 to 11, and the method comprises reducing the moiré pattern by modifying the switching voltage.

13. The method of claim 12, wherein modifying the switching voltage comprises applying the following sequence of steps: 1) Increase the voltage between the two planar switching electrodes; then 2) Observe the naked eye stereoscopic display device and check whether a moiré pattern can be observed; then 3) If a moiré pattern is observed, determine whether to reduce the moiré pattern; and then 4) If the moiré pattern needs to be reduced, method steps 1) to 4) are repeated until the moiré pattern is no longer observed; or until an acceptable moiré pattern is observed.

14. A method for manufacturing a naked-eye stereoscopic display device, the method comprising: - providing a naked eye stereoscopic display device according to any one of claims 1 to 11; then - Performing a method according to claim 12 or 13.

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