Moire Reduction in an Auto-Stereoscopic Display Device

Abstract

The present invention relates to a 2D / 3D switchable autostereoscopic display device optimized to exhibit reduced moiré. This is done by providing a nanorelief structure on the surface in contact with the liquid crystal switching medium. As a result, scattering occurs, and as a result, moiré is reduced. The amount of scattering can be affected by changing the electric field applied to the liquid crystal medium. The present invention further relates to a method for reducing moiré in an autostereoscopic display device and a method for manufacturing an autostereoscopic display device.

Description

Technical Field

[0001] The present invention relates to an autostereoscopic display device with reduced moire (or interference fringes), a method for reducing moire in an autostereoscopic display device, and a method for manufacturing an autostereoscopic display device with reduced moire.

Background Art

[0002] A display that can be electrically switched between a 2D view mode and a 3D view mode is generally known as a 2D / 3D switchable autostereoscopic display and has received significant attention in the past 20 years. A common approach is to use a lenticular device that includes an array of semi-cylindrical microlenses (lenticulars) adjacent to a liquid crystal medium that can be switched between two liquid crystal orientations under the influence of an electric field, and arrange an array of pixels (or picture elements) in a row. In the first orientation, the director (or orientation vector) of the liquid crystal medium is in the plane of the display, and in the second orientation, the director of the liquid crystal medium is perpendicular to the plane of the display.

[0003] In such a setup, each lenticular is associated with a group of at least two columns of (sub) pixels that extend parallel to or at an angle (tilted) with respect to the lens. The pixel output that travels through the lenticular device is subject to the optical properties of the lenticular and the liquid crystal medium. The refractive index of the lenticular is fixed, while the refractive index of the adjacent liquid crystal medium can be switched between two values by switching between two liquid crystal alignments, i.e., 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. The pixel output "sees" either the first refractive index or the second refractive index when traveling substantially perpendicular to the plane of the display. In the first view mode, the liquid crystal medium is in the first alignment. Its refractive index matches that of the lenticular, thereby robbing the lenticular of its focusing effect and causing the lenticular device to behave as a transparent and flat optical panel. This forms the 2D view mode of the autostereoscopic display. In the second view mode, the liquid crystal medium is in the second liquid crystal alignment. Since the two refractive indices do not match, each lenticular can exhibit a focusing effect. This makes it possible to direct the outputs from different pixel columns to different spatial positions in front of the autostereoscopic display, which enables the viewer to perceive a 3D image composed of a left image and a right image. This forms the 3D view mode of the autostereoscopic display.

[0004] A problem with many 2D / 3D - switchable autostereoscopic displays is that due to the superposition of the pattern of the pixel array and the pattern of the lenticular array, the viewer perceives a moiré pattern. Such patterns are usually obtrusive to the viewer. Furthermore, the moiré makes the screen itself visible, as does reflection for example. This brakes the illusion of a "floating" three - dimensional image in the space in front of or behind the screen.

[0005] To date, much effort has been expended to reduce or even completely cancel moiré patterns in this type of display. For example, it is possible to identify the pixels that contribute most to moiré and then modify (or change / modify) their pixel outputs in a specific way. However, this has undesirable side effects such as a decrease in resolution and a decrease in display intensity. It also requires valuable processor capacity. Other solutions relate to the use of specific pixel shapes and pixel arrangements in combination with specific lenticular tilt angles. However, since this can cause moiré even with a small tilt deviation, it limits the design opportunities for autostereoscopic display devices and makes the manufacturing process more critical.

Disclosure of the Invention

Problems to be Solved by the Invention

[0006] Accordingly, an object of the present invention is to find a solution to the appearance of moiré patterns, particularly a solution that does not exhibit one or more of the above-mentioned side effects. It is also an object to provide a solution that is less complex than solutions known in the art. More generally, an object of the present invention is to improve the viewing experience of viewers of autostereoscopic displays.

Means for Solving the Problems

[0007] It has been found that one or more of these objectives can be achieved by applying specific modifications to the surface adjacent to the liquid crystal medium in a switchable (or switchable / switchable) autostereoscopic display.

[0008] Accordingly, the present invention relates to an autostereoscopic display device (10) that can be electrically switched from a first view mode to a second view mode, the autostereoscopic display device (10) comprising - A display panel (1) having an array of display pixel elements (or display pixel elements) for generating a display output (or display output); - A lenticular device (2) provided on the display panel (1) that can be electrically switched to provide a first view mode or a second view mode. In one of the two view modes, the lenticular device (2) enables the display of an autostereoscopic image composed of a left image and a right image. The lenticular device (2) has a lenticular lens region that can direct the display output from different display pixel elements to different spatial positions within the field of view of the autostereoscopic display device (10). The lenticular device (2) 〇 A first optically transparent substrate (4) including an array of lenticular elements provided on the first optically transparent substrate (4). The lenticular elements have a first surface (4a) having liquid crystal alignment properties, the substrate (4); 〇 A second optically transparent substrate (5) having a second surface (5a) with liquid crystal alignment properties. The first surface (4a) and the second surface (5a) face each other, the substrate (5); 〇 A first planar switching electrode (6) disposed on the side of the first optically transparent substrate (4); 〇 A second planar switching electrode (7) disposed on the side of the second optically transparent substrate (5); 〇 A liquid crystal medium (8) containing liquid crystal molecules (9). The liquid crystal medium (8) is sandwiched between two substrates (4, 5) and is in contact with the first surface (4a) and the second surface (5a). 1. In the first view mode, the liquid crystal molecules (9) are in the plane of the planar switching electrodes (6, 7) (or lying in the plane of the planar switching electrodes (6, 7)); 2. In the second viewing mode, the lenticular device (2) includes the liquid crystal medium (8) in which the liquid crystal molecules (9) are oriented perpendicular to the two planar switching electrodes (6, 7). - Means (3) for applying a switching voltage between both planar switching electrodes (6, 7) to perform switching from the first viewing mode to the second viewing mode (or, switching), The first surface (4a) and / or the second surface (5a) has a surface relief structure (11) with surface relief dimensions, which causes scattering of the display output when the liquid crystal molecules (9) included in the surface relief structure (11) have an orientation that provides a refractive index different from that of the surface relief structure (11).

[0009] The present invention further relates to a method for reducing moiré in an autostereoscopic display device, the autostereoscopic display device being the autostereoscopic display device (10) defined above, and the method includes modifying a switching voltage to reduce moiré.

[0010] The present invention further relates to a method for manufacturing an autostereoscopic display device, the method including: - Providing the autostereoscopic display device described above, - Executing the method described above.

Brief Description of the Drawings

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Figure 1

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DETAILED DESCRIPTION OF THE INVENTION

[0012] The elements in the figures are shown simply and clearly and are not necessarily drawn to scale. For example, the dimensions of some elements in the figures may be exaggerated relative to other elements to assist in understanding the various exemplary embodiments of the present invention. For example, the relative dimensions of the different components of an autostereoscopic display device cannot be derived from the drawings. This relates, for example, to the dimensions of the nano-relief structure relative to the dimensions of the lenticular elements and the schematic liquid crystal molecules. Also, it is not possible to derive how the dimensions of the nano-relief structure itself differ from each other (e.g., the height of the ridges, the width of the ridges, and the width of the valleys).

[0013] Furthermore, terms such as "first", "second", etc. in this specification and the claims, if any, are generally used to distinguish similar elements and are not necessarily used to describe a sequential or chronological order.

[0014] In the context of the present invention, the term "viewer" means a person who can, in particular, view the content presented by an autostereoscopic display device. Throughout the present text, references to the viewer are made in masculine terms such as "he", "him", or "his". This is for the purposes of clarity and brevity only, and it is understood that feminine terms such as "she", "her", and "hers" apply equally.

[0015] In the context of the present invention, the term "moiré" means the viewer's perception of a pattern ("moiré pattern") that appears due to the superposition of two actual (or real) patterns that are slightly displaced, slightly rotated, and / or have slightly different pitches. Also, moiré can occur when the pitch of one pattern is approximately (but not exactly) an integer (2, 3, 4, etc.) multiple of the pitch of the other pattern. The moiré that is reduced or overcome in the present invention typically relates to the superposition of the pattern of the pixel array and the pattern of the lenticular array.

[0016] It is understood that the liquid crystal medium is a birefringent material having a first refractive index for linearly polarized light traveling along the director of the liquid crystal medium and a second refractive index for linearly polarized light traveling perpendicular to the director of the liquid crystal medium. When the term "refractive index" is used throughout the present text with respect to the liquid crystal medium, unless otherwise specified, this refers to the refractive index of the liquid crystal medium in a direction perpendicular to the plane-switching electrodes, i.e., the direction in which the display output (i.e., linearly polarized light) travels. This refractive index can also refer to the first refractive index or the second refractive index defined above, depending on the electric field applied across the liquid crystal medium.

[0017] In the autostereoscopic display device of the present invention, a liquid crystal medium exists between two opposing surfaces, i.e., the liquid crystal medium is in contact with both surfaces. These relate to a first surface which is the surface of a lenticular element provided 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 lenticular in shape, while the second surface can in principle have any shape. However, usually, the second surface is a flat surface or a lenticular surface. In the latter case, there are two opposing lenticular surfaces.

[0018] The liquid crystal medium contains liquid crystal molecules. Two planar switching electrodes are arranged on both sides of the liquid crystal medium and can apply an electric field to the liquid crystal medium. The liquid crystal molecules can be oriented in the plane of the planar switching electrodes under the influence of the alignment characteristics of the surfaces, or can be perpendicular to the plane of the planar switching electrodes under the influence of a voltage applied across both planar switching electrodes. Each of these two different orientations gives rise to a different viewing mode.

[0019] These two view modes are shown in FIGS. 1 and 2 respectively, which show cross-sectional views of the liquid crystal cell of the autostereoscopic display device (10) of the present invention. It comprises a lenticular device (2) provided on a display panel (1) having an array of display pixel elements for generating a display output. The lenticular device (2) includes a liquid crystal medium (8) containing liquid crystal molecules (9). The liquid crystal medium (8) is sandwiched between two optically transparent substrates (4, 5), and these substrates 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 lenticular device (2) is electrically switchable to provide a first view mode or a second view mode. This switching is performed by applying a switching voltage between the two planar switching electrodes (6, 7) provided with means (3). The liquid crystal molecules (9) in FIG. 1 have their elongated directions perpendicular to the plane in which the figure is shown. The liquid crystal molecules (9) in FIG. 2 have their elongated directions parallel to the plane in which the figure is shown.

[0020] In the absence of a potential, the molecules are oriented in the plane of the planar switching electrodes according to the liquid crystal alignment characteristics of the first and second surfaces, defining the first view mode. When a sufficiently strong potential ("switching voltage") is applied, they switch to an orientation that coincides with the corresponding electric field perpendicular to the plane of the planar switching electrodes, defining the second view mode. Thus, the switching voltage is the voltage at which the autostereoscopic display device changes to its second view mode and remains in the second view mode. Usually, there is a threshold voltage at which the change to the second view mode takes place. Thus, the switching voltage is, in principle, any voltage exceeding this threshold voltage.

[0021] In an auto-stereoscopic display device that can be electrically switched between two view modes, there is a switching from one liquid crystal alignment to another. This is caused by changing the electric field received by the liquid crystal medium. The bulk of the liquid crystal medium follows this electric field, causing a switching that occurs uniformly throughout the medium. However, this is less applicable at the interface between the liquid crystal medium and the surface having liquid crystal alignment characteristics. Here, the liquid crystal molecules are fixed to the surface that aligns them under the influence (or fluence) of an anchoring force (or, adhesion force / anchoring force). They have substantially no degree of freedom of orientation and particularly have a first layer of liquid crystal molecules. As a result, when the liquid crystal molecules are aligned on and within the plane of the surface, the liquid crystal molecules are less likely to switch to an orientation perpendicular to the surface than the bulk portion. This is due to the force of adhesion, resulting in a situation where the bulk (i.e., molecules further away from the surface) performs the switching and the small layer adjacent to the surface does not. In the context of the present invention, this layer is referred to as the "boundary layer". The boundary layer does not have a discontinuous transition to the bulk, but it is presumed that the adjacent liquid crystal molecules gradually adapt their orientation to the orientation of the bulk.

[0022] The existence of the boundary layer has the effect that the refractive index of the liquid crystal medium near the surface is different from that of the bulk. This means that it is possible to create a state in which a part of the liquid crystal medium has a refractive index that matches the refractive index of the material surrounding the liquid crystal medium (typically a lenticular element and a second optically transparent substrate), and another part has a refractive index that does not match. This leads to two situations, namely, 1) the refractive index of the boundary layer matches the refractive index of the surrounding material, but the refractive index of the bulk is different, and 2) the refractive index of the bulk matches the refractive index of the surrounding material, but the refractive index of the boundary layer is different.

[0023] The first situation has the effect that the display output (i.e., light) of the display pixel elements passing through the surrounding material "experiences" that the surrounding material is slightly thicker than it actually is. This is because light travels a longer distance through a medium with a specific refractive index. In other words, as far as refraction is concerned, light "sees" no difference between the surrounding material and the boundary layer.

[0024] The present invention utilizes this first situation for moiré reduction.

[0025] First, a nano-relief structure is introduced on the surface of the surrounding material (or a part thereof). This structure scatters the pixel output and reduces moiré.

[0026] Second, the degree of scattering can be controlled by increasing the thickness of the boundary layer. When the boundary layer is thin, the nano-relief structure is very "visible" to the pixel output. The thicker the boundary layer, the more the nano-relief structure is "immersed" by it and becomes "invisible" to the pixel output. This is due to the effect outlined above, specifically the effect occurring in situation 1). Here, the structural features of the nano-relief structure are surrounded by a medium with the same refractive index, which effectively deprives them of their light-scattering characteristics.

[0027] The thickness of the boundary layer can be adjusted by changing the switching voltage. The higher the voltage (and thus the electric field), the higher the force induced to overcome the surface adhesion force and to switch the orientation of the liquid crystal molecules close to the surface where the liquid crystal molecules are aligned. Therefore, by changing the switching voltage, the severity of scattering can be affected.

[0028] The inventors have found that the occurrence of moiré can be reduced by applying an appropriate electric field.

[0029] Theoretically, it is further considered that, as a side effect of the preferred scattering, crosstalk may increase. Crosstalk means a phenomenon in which a (small) part of the light from the display pixel elements targeted at the left eye reaches the right eye in an auto-stereoscopic display, or the reverse phenomenon. Hereinafter, it will be described how the present invention can solve the final occurrence of crosstalk caused by scattering.

[0030] As described above, the thickness of the boundary layer can be adjusted by changing the switching voltage. Thereby, the degree of scattering of the pixel output changes, affecting the moiré pattern. Therefore, according to the present invention, moiré can be reduced by appropriately adjusting the voltage between the two-plane switching electrodes. Therefore, an important element of the auto-stereoscopic display device of the present invention is means for applying such a switching voltage to the two-plane switching electrodes.

[0031] In one embodiment, this means (3) is configured to apply a switching voltage that enables the nano-relief structure to scatter the display output and reduce moiré. In this embodiment, this means is manufactured with a switching voltage that has been proven to have less moiré than other switching voltages and / or to optimally achieve the best results in terms of moiré and image quality. This is typically a factory setting and remains the same throughout the entire life of the display device.

[0032] In another embodiment, the above means can apply at least two different magnitudes of switching voltage. In this embodiment, it is possible to select the switching voltage that brings about the maximum reduction of moiré. Thus, according to this embodiment, the settings of the auto-stereoscopic display device can be optimized.

[0033] This may be performed in a factory as part of the manufacture of an autostereoscopic display device. Since even a slight small (tilt) deviation can cause moiré, the manufacturing process usually has very small tolerances. If it is possible to improve the occurrence of moiré after manufacturing, these tolerances can be widened, which is advantageous.

[0034] Also, during manufacturing, the parameters of the lenticular device (e.g., pitch, tilt) and the nano-relief structure parameters can first be selected to be approximately correct. Next, after assembling the autostereoscopic display device from its different components, fine adjustment can be performed for each product or for each product series by setting an appropriate switching voltage. Conventional autostereoscopic display devices require several iterative cycles in design and manufacturing, but these can be skipped in the autostereoscopic display device of the present invention.

[0035] Optimization of the settings of the autostereoscopic display device may alternatively be performed by the viewer of the device at his or her discretion, typically when obstructed by a moiré pattern. Thus, in one embodiment, the autostereoscopic display device of the present invention is designed to allow the viewer of the autostereoscopic display device to reduce moiré by adjusting the switching voltage.

[0036] If the means for applying the switching voltage can apply at least two switching voltages of different magnitudes, their number is usually more than 2, for example, at least 3, at least 4, at least 5, at least 7, or at least 10. It may also be at least 15, at least 25 or at least 50. It may also be continuously variable.

[0037] The nano-relief structure is a surface relief on the surface of the lenticular elements of the first optically transparent substrate and / or on the surface of the second optically transparent substrate. This means that the nano-relief structure is a structure that is superimposed on each surface. Since the surface of the first optically transparent substrate is a lenticular surface (i.e., the surface of the lenticular element), the nano-relief structure is superimposed on this lenticular surface. Similarly, since the surface of the second optically transparent substrate is a flat surface, the nano-relief structure is superimposed on this flat surface. This is shown in FIGS. 3 and 4, which show an enlargement of a part of a cross-section of the liquid crystal cell of the autostereoscopic display device (10) of the present invention (FIGS. 1 and 2 show a larger part of such a cell but are not shown in more detail). FIGS. 3 and 4 show cross-sections of the nano-relief structure (11) on each of the optically transparent substrates (4, 5).

[0038] FIG. 3 shows a cross-section of the nano-relief structure (11) superimposed on the first optically transparent substrate (4). This is a cross-section of the lenticular element of the first optically transparent substrate (4) (perpendicular to its elongated direction). Along the curve of the lenticular cross-section, there are a number of adjacent valleys and ridges (also seen perpendicular to the cross-section with respect to their elongated direction). The first surface (4a) of the first optically transparent substrate (4) is formed by the valleys and ridges.

[0039] FIG. 4 shows a cross-section of the nano-relief structure (11) superimposed on the second optically transparent substrate (5). Along the straight cross-section of the second optically transparent substrate (5), there are a number of adjacent valleys and ridges (seen perpendicular to the cross-section with respect to their elongated direction). The second surface (5a) of the second optically transparent substrate (5) is formed by the valleys and ridges.

[0040] The liquid crystal medium (8) is sandwiched between two optically transparent substrates (4, 5) and is in contact with their respective surfaces (4a, 5a), so that the nano-relief structure is completely immersed in the liquid crystal medium (8). This means that the liquid crystal molecules (9) completely fill the valleys of the nano-relief structure, and as a result, the surfaces of the valleys and ridges are at the interfaces between the respective optically transparent substrates (4 or 5) and the liquid crystal medium (8).

[0041] The nano-relief structure has surface relief dimensions that cause scattering of the display output when the nano-relief structure is illuminated by the display output, for example when the display output passes through it (and through each optically transparent substrate of which the nano-relief structure forms part). This design requirement depends on the situation where the nano-relief structure (or part thereof) has an interface with a liquid crystal medium having a refractive index that does not match the refractive index of the nano-relief structure (and thus the refractive index of each optically transparent substrate of which the nano-relief structure forms part) when the liquid crystal molecules are oriented perpendicular to two planar switching electrodes. This requires that the liquid crystal molecules having this normal orientation be included in the nano-relief structure, i.e., that they be present in the valleys between the ridges of the nano-relief structure. In other words, this relates to the situation where the boundary layer does not completely cover the nano-relief structure, and thus at least a part of the nano-relief structure (especially its ridges) is present within the bulk of the liquid crystal medium in which the liquid crystal molecules are oriented perpendicular to two planar switching electrodes. In this way, the nano-relief structure becomes "visible" to the display output and thus causes scattering of the display output.

[0042] This is visualized in Figure 5, showing a graph (20) of the height of the nano-relief structure (11) as a function of the direction on the surface. On the left side, a thick boundary layer (12) is superimposed on the graph (20), and on the right side, a thin boundary layer (13) is superimposed on the graph (20). The liquid crystal molecules (14) in the thick boundary layer (12) are present only "above" the nano-relief structure, while the liquid crystal molecules (15) in the thin boundary layer (13) are also present between the peaks (or ridges) of the nano-relief structure (11).

[0043] To truly achieve the required scattering, the nano-relief structure needs to have appropriate dimensions for the scattering of the display output. A person skilled in the art knows how to create and implement such a nano-relief structure by routine experiments without exerting the efforts of the present invention.

[0044] For example, the surface features responsible for scattering usually have at least one dimension in the range of 1 to 1,000 nm, preferably in the range of 1 to 500 nm.

[0045] Normally, the height of the nano-relief structure (and thus the surface features) is 1,000 nm or less, preferably 500 nm or less. A large relief height requires a thick boundary layer on the lens to achieve a certain amount of scattering. Since this thick boundary layer is significantly added to the lens, it effectively causes deformation of the lens. Since the deformation of the lens is preferably minimized (especially crosstalk that impairs the viewing field), it is preferable that the height of the nano-relief structure (and thus the surface features) is limited.

[0046] The nano-relief structure preferably is not periodic and / or does not have a regular structure because this can result in a moiré pattern.

[0047] Preferably, the nano-relief structure includes substantially parallel grooves. When these are oriented horizontally, they offer the advantage of minimizing horizontal scattering. This also minimizes scatter-induced crosstalk, since crosstalk is a result of horizontal light aberration. Crosstalk refers to the phenomenon (a small) portion of light from a display pixel element intended for the left eye reaching the right eye in an autostereoscopic display, or vice versa, i.e., the phenomenon of horizontal deviation. Crosstalk degrades the quality of the perceived three-dimensional view. Horizontal grooves mainly have the property of scattering light in the vertical direction, and crosstalk is hardly sensitive to vertical scattering. Thus, when grooves are present, they are preferably oriented horizontally (i.e., extending between left and right within the viewer's field of view). This means that the grooves preferably extend parallel to the lateral direction in which the left and right images are displaced, i.e., the lateral displacement between the left and right images configured to be generated by the autostereoscopic display device. The grooves may also extend in a direction deviating less than 30° or less than 20° from such a lateral direction, preferably less than 10° or less than 5°.

[0048] An autostereoscopic display device is usually rectangular and is usually viewed in the lateral direction (not the vertical direction), so the groove direction usually corresponds to the long direction of the device. This direction ideally corresponds to the direction between the viewer's pupils, i.e., the direction of the virtual line connecting both eyes. In practice, the viewer moves and rotates with respect to the display device, resulting in temporal variations in direction.

[0049] Usually, the height of the grooves is 1,000 nm or less. Preferably, since more lens deformation occurs as the height increases, it is 500 nm or less (see the above explanation). Their width is usually in the range of 50 to 5,000 nm. Their length is usually at least 10 μm. For example, it is in the range of 10 to 10,000 μm, or in the range of 20 to 2,000 μm.

[0050] The grooves are preferably not periodic and / or do not have a regular structure because this can result in a moiré pattern. Their lengths are not limited in principle, but it is conceivable that a plurality of very long (and parallel) grooves can also produce a moiré effect.

[0051] When the nano-relief structures exist as grooves, there are two surface characteristics defined by their directions, namely the grooves and the liquid crystal alignment. In a preferred embodiment, both directions are the same or substantially the same. Thus, in the autostereoscopic display device according to the present invention, the liquid crystal alignment characteristics include the characteristics of aligning liquid crystal molecules in a direction along the direction of the substantially parallel grooves.

[0052] However, the nano-relief structure can also include surface features without preferring a specific direction. For example, the nano-relief structure includes surface features with a random orientation having a length, a width, and a height, - the width and the length are independent of each other in the range of 50 to 5,000 nm, - the height is in the range of 1 to 500 nm, - the length is not more than 4 times the width.

[0053] Generally, the nano-relief structure is preferably designed such that more than 50%, preferably more than 80%, more preferably more than 90% of the scattered display output is scattered in a direction perpendicular to the left-right direction set by the lateral displacement of the left and right images, i.e., the lateral displacement direction in which the left and right images generated by the autostereoscopic display device are displaced. The above direction may also be deviated by less than 30°, or less than 20°, or less than 10°, or less than 5° from such a lateral direction. This direction is ideally perpendicular to the direction between the observer's pupils, i.e., the direction of the virtual line connecting both eyes.

[0054] The autostereoscopic display device is usually rectangular and is usually viewed in the horizontal (rather than vertical) direction, so the scattering direction usually corresponds to the short direction of the device.

[0055] The nano-relief structure is present on one or both of the surfaces between which the liquid crystal medium is sandwiched. Thus, in the autostereoscopic display device according to the invention, - the nano-relief structure is present on the first surface and not on the second surface, or - the nano-relief structure is present on the second surface and not on the first surface, or - the nano-relief structure is present on the first and second surfaces.

[0056] The invention further relates to a method for reducing moiré in an autostereoscopic display device, said autostereoscopic display device being an autostereoscopic display device as described above, said method comprising modifying a switching voltage in order to reduce moiré.

[0057] This method basically uses an autostereoscopic display device according to the invention as described above, including all embodiments as described above.

[0058] The method according to the invention comprises optimizing the switching voltage in order to reduce moiré. This typically includes modifying the switching voltage, in particular increasing the switching voltage. This may be carried out during the manufacture of the autostereoscopic display device (typically after the assembly of the main components) or by the observer. Since moiré is difficult to capture with a camera (this may even introduce moiré into the camera recording), the optimization is preferably carried out manually, i.e. by a person.

[0059] In one embodiment, optimizing the switching voltage comprises applying the following sequence of steps: 1) increasing the voltage between two planar switching electrodes by a constant amount, and then 2) observing the autostereoscopic display device and checking whether a moiré pattern can be observed, and then 3) If a moiré pattern can be observed, a step of determining whether it is desirable to reduce it, and then 4) If it is desirable to reduce it, repeating method steps 1) to 4) until the moiré pattern can no longer be observed or until an acceptable moiré pattern can be observed.

[0060] Preferably, in this method, the final presence of crosstalk is also considered. This can be implemented by method steps in which it is checked whether crosstalk exists and it is determined whether it is desirable to reduce it.

[0061] As described above, an appropriate voltage for reducing moiré may be incorporated as a factory setting into the autostereoscopic display device of the present invention. Therefore, the method of the present invention can also be used during the manufacture of the autostereoscopic display device of the present invention. Accordingly, the present invention further relates to a method of manufacturing an autostereoscopic display device, the method comprising: - providing the above-described autostereoscopic display device, and - implementing the method as described above. <Example>

[0062] An aperiodic nano-relief structure was created in a flat copper sheet using unidirectional mechanical abrasion. This unidirectional nano-relief structure is represented by structure (11) of graph (20) in FIG. 5. A photopolymerizable resin was poured onto the copper nano-relief structure, an ITO glass plate was placed on top, and then UV curing was performed. After peeling from the copper sheet, a glass plate having a cured resin was obtained, and a unidirectional nano-relief structure was present on the cured resin.

[0063] A rubbed polyimide-coated glass plate was provided, with an ITO glass plate sandwiched between the polyimide and the glass.

[0064] Next, a twisted nematic liquid crystal cell was prepared by using a nano-relief glass plate and a rubbed polyimide-coated glass plate, where the nano-relief structure faced the rubbed polyimide side. The cell was a capillary filled with a twisted nematic liquid crystal and closed with an adhesive. After attaching wires, a curing process was performed at a high temperature.

[0065] Next, the setup was performed as shown in FIG. 7. The light (21) of the laser pointer (22) was transmitted through the liquid crystal cell (23), and the egressing light (24) was projected onto a piece of paper (25) so as to be visible to the observer (26). The one-directional nano-relief structure was oriented perpendicular to the plane of FIG. 7. There was means (27) for applying a switching voltage, and a continuously variable voltage could be applied to the liquid crystal cell (23). A voltmeter (not shown) indicating the applied voltage was also visible to the observer (26). Depending on the voltage, a part of the egressing light (24) was scattered light 24a, which was also projected onto the paper (25).

[0066] An electric field was applied to the liquid crystal cell by slowly increasing the voltage from zero to 30V. Up to about 11V, the projection of the egressing light (24) on the paper (25) was sharp, which means that the laser light (21) was not refracted / scattered. At about 11V, the laser light (21) began to refract perpendicular to the one-directional nano-relief structure. This effect was enhanced up to about 18V and then remained constant. The six photographs in FIG. 6 show various stages during the voltage increase. The indication of the actually applied voltage is in front of each photograph, and a piece of paper (25) is present in the background.

Claims

1. An autostereoscopic display device (10) that can be electrically switched from a first view mode to a second view mode, wherein the autostereoscopic display device (10) comprises: - A display panel (1) having an array of display pixel elements for generating a display output; - A lenticular device (2) provided on the display panel (1) that can be electrically switched to provide the first view mode or the second view mode. In one of the two view modes, the lenticular device (2) is capable of directing the display output from different display pixel elements to different spatial positions within the field of view of the autostereoscopic display device (10) so as to enable the display of an autostereoscopic image composed of a left image and a right image. The lenticular device (2) comprises: 〇 A first optically transparent substrate (4) including an array of lenticular elements, wherein the lenticular elements have a first surface (4a) with liquid crystal alignment characteristics; 〇 A second optically transparent substrate (5) having a second surface (5a) with liquid crystal alignment characteristics, wherein the first surface (4a) and the second surface (5a) face each other; 〇 A first planar switching electrode (6) disposed on the side of the first optically transparent substrate (4); 〇 A second planar switching electrode (7) disposed on the side of the second optically transparent substrate (5); 〇 A liquid crystal medium (8) containing liquid crystal molecules (9), wherein the liquid crystal medium (8) is sandwiched between the two optically transparent substrates (4, 5) and is in contact with the first surface (4a) and the second surface (5a); 1. In the first view mode, the liquid crystal molecules (9) are in the plane of the planar switching electrodes (6, 7); 2. In the second view mode, the liquid crystal molecules (9) are oriented perpendicular to the two planar switching electrodes (6, 7). The lenticular device (2) includes the liquid crystal medium (8). - Means (3) for applying a switching voltage between both planar switching electrodes (6, 7) to effect a switch from the first view mode to the second view mode, The nano-relief structure (11) is - On the first surface (4a) of the lenticular element of the first optically transparent substrate (4) and / or - On the second surface (5a) of the second optically transparent substrate (5), The nano-relief structure (11) is - Comprising valleys between the ridges, the valleys being filled with liquid crystal molecules (9) of the liquid crystal medium (8), - An auto-stereoscopic display device (10) capable of scattering the display output when illuminated by the display output and when the liquid crystal molecules (9) contained in the valleys of the nano-relief structure (11) have an orientation providing a refractive index different from that of the nano-relief structure (11) to the liquid crystal medium (8) within the valleys.

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

3. The means (3) for applying a switching voltage is capable of applying at least two different magnitudes of switching voltage, the auto-stereoscopic display device (10) according to claim 1 or 2.

4. The auto-stereoscopic display device (10) is designed such that a viewer of the auto-stereoscopic display device (10) can reduce moiré by adjusting the switching voltage, the auto-stereoscopic display device (10) according to any one of claims 1 to 3.

5. The nano-relief structure comprises grooves substantially parallel to a direction parallel to the lateral direction in which the left and right images configured to be generated by the auto-stereoscopic display device (10) are displaced, or a direction deviating less than 10° from the lateral direction, the auto-stereoscopic display device (10) according to any one of claims 1 to 4.

6. The auto-stereoscopic display device (10) according to claim 5, wherein the groove has a height in the range of 1 to 1,000 nm and a width in the range of 50 to 5,000 nm.

7. The auto-stereoscopic display device (10) according to claim 5 or 6, wherein the liquid crystal alignment characteristic includes a characteristic of aligning liquid crystal molecules in a direction along the direction of the substantially parallel grooves.

8. The nano-relief structure includes surface features of random orientation having a length, a width, and a height, - the width and the length are, independently of each other, in the range of 50 to 5,000 nm, - the height is in the range of 1 to 500 nm, - the length is not more than 4 times the width, the auto-stereoscopic display device (10) according to any one of claims 1 to 4.

9. The nano-relief structure is designed such that more than 50%, preferably more than 80% of the scattered display output is scattered in a direction perpendicular to the lateral direction in which the left image and the right image generated by the auto-stereoscopic display device (10) are displaced, or in a direction deviating less than 10° from the lateral direction, the auto-stereoscopic display device (10) according to any one of claims 1 to 8.

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

11. The nano-relief structure is not periodic and / or does not have a regular structure, the auto-stereoscopic display device (10) according to any one of claims 1 to 10.

12. A method for reducing moiré in an auto-stereoscopic display device, wherein the auto-stereoscopic display device is the auto-stereoscopic display device (10) according to any one of claims 1 to 11, and the method includes modifying the switching voltage to reduce moiré.

13. Modifying the switching voltage comprises 1) increasing the voltage between the two planar switching electrodes, and then 2) observing the autostereoscopic display and checking whether a moiré pattern can be observed, and then 3) determining whether it is desirable to reduce it if a moiré pattern can be observed, and then 4) repeating method steps 1) to 4) until the moiré pattern can no longer be observed or an acceptable moiré pattern can be observed if it is desirable to reduce it, The method according to claim 12, comprising sequentially performing the steps above. **Claim 14** A method of manufacturing an autostereoscopic display device, the method comprising - providing an autostereoscopic display device according to any one of claims 1 to 11, and then - performing the method according to claim 12 or 13.

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