Optical element and manufacturing method thereof

Abstract

To provide a planar optical element that can have a predetermined influence on the diffusion direction of incident light and can be optionally switched between at least two operating states, namely, a free-viewing mode and an anti-peeping mode. [Solution] The present invention relates to an optical element (1) having a planar surface and a light entrance side and a light exit side. The optical element (1) includes alternating transparent first and second regions (B1 and B2) made of materials having different first and second refractive indices (N1 and N2), where the first refractive index (N1) is greater than the second refractive index (N2). Opaque or switchable opaque first and second layers (OB and AB) are disposed on the light entrance and light exit surfaces of the second region (B2). The opaque layers (OB and AB) restrict the diffusion direction of light passing through the optical element (1) compared to the transparent layers (OB and AB).

Description

[Technical Field]

[0001] In recent years, the viewing angle of liquid crystal displays has been greatly expanded.

[0002] However, there are often situations where the wide viewing angle of a screen can be a drawback. Mobile devices, such as laptops and tablets, are increasingly used to store personal and confidential information, such as bank account details. Therefore, it is necessary to control who can view this confidential data. For example, when viewing vacation photos or for promotional purposes, a wide viewing angle is required to share the information on the display with others. On the other hand, if you want to keep the image information secret, a narrower viewing angle is required.

[0003] A similar problem exists in car manufacturing: the driver must not be distracted by visual content, such as digital entertainment programs, while the engine is running, but passengers want to enjoy them while driving, so a screen with a switchable display mode is needed. [Background technology]

[0004] To achieve visual data protection on portable displays, additional films with microlouvers have already been used. However, these films are not (re)switchable and must always be manually applied and then removed. They also have to be carried separately from the display even when not needed. Furthermore, the use of such louvered films has the significant drawback of causing light loss.

[0005] US Patent Application No. US6765550B2 describes such a microlouver to prevent peeping, the biggest drawbacks of which are the mechanical removal or installation of the filter and the loss of light in the protection mode.

[0006] US Patent Application No. US5993940A describes the use of a film with small prism stripes uniformly arranged on its surface to achieve a privacy mode, which is quite costly to develop and manufacture.

[0007] In international patent application WO2012 / 033583A1, switching between free and restricted viewing is achieved by manipulating liquid crystals between so-called "chromonic" layers, which incurs significant light losses and costs.

[0008] US Patent Application No. US2012 / 0235891A1 describes a highly complex backlighting system within a screen. According to Figures 1 and 15, not only are multiple light guides used, but other complex optical elements, such as microlens elements 40 and prism structures 50, are also used to convert light on its way from rear lighting to front lighting. These are expensive and complex to implement, and also involve light losses. According to a variant shown in Figure 17 of US Patent Application No. US2012 / 0235891, both light sources 4R and 18 generate light with a narrow illumination angle, while the light from the rear light source 18 is painstakingly converted to light with a wide illumination angle. As already mentioned above, this complex conversion significantly reduces brightness.

[0009] According to Japanese Patent Application JP2007-155783A, special optical surfaces 19 that are painstakingly calculated and manufactured are used to deflect light into various narrow or wide areas depending on the angle of incidence. These structures are similar to Fresnel lenses. Furthermore, there are interference edges that deflect light in undesired directions. Therefore, it remains unclear whether a practical light distribution can actually be achieved.

[0010] U.S. Patent Application No. US2013 / 0308185A1 describes a special stepped light guide that emits light in various directions on its major surface depending on the direction from which the light is emitted from the narrow side. This allows for the creation of a screen that can be switched between free-viewing and limited-viewing modes when combined with a transmissive image display device, such as an LC display. The drawback is that the limited-viewing effect can only be generated horizontally or vertically, but not simultaneously, as may be required for certain payment transactions. Furthermore, even in limited-viewing mode, afterglow is always visible from blocked viewing angles.

[0011] The applicant's international patent application WO 2015 / 121398 A1 describes a screen with two operating modes, in which scattering particles are essential for switching between operating modes within the corresponding light guide volume. However, the polymeric scattering particles selected therein have the disadvantage that light is generally emitted from both major surfaces, resulting in approximately half of the available light being emitted in the wrong direction, i.e., towards the backlight, where it cannot be fully recycled due to the structure. Furthermore, the polymeric scattering particles distributed throughout the light guide volume may, in some cases, lead to scattering effects that reduce the anti-peeping effect in the protected operating mode, especially at high concentrations.

[0012] The drawbacks that the above methods and arrangements generally share are that they significantly reduce the brightness of the basic screen, and / or require complex and expensive optics for mode switching, and / or provide only limited protection against peeping, and / or reduce the resolution in free viewing mode, and / or only allow a narrow viewing range, so that the brightness falls off rapidly across the angular spectrum and the viewer sees an image that is very non-uniform in terms of brightness. Summary of the Invention

[0013] The objective of the present invention is therefore to develop a planar optical element that can affect the diffusion direction of incident light and can be optionally switched between at least two operating states: a free-viewing mode and an anti-peeping mode, where light exits the optical element only in a limited angular range, i.e., with a smaller diffusion direction, compared to the free-viewing mode. The optical element should be inexpensive to implement and be compatible with various types of screens, particularly to allow switching between the anti-peeping mode and the free-viewing mode, with substantially no or only negligible degradation of the resolution of such screens. Furthermore, the optical element should offer the possibility of achieving a light distribution that is essentially top-hat shaped. This means that the brightness does not decrease by more than 15% within an angular range of at least 7 degrees around the mean emission angle.

[0014] The above problem is solved by a planar optical element having a light input side and a light output side, the planar optical element including first regions made of a first transparent material having at least a first refractive index and second regions made of a second transparent material having a second refractive index, the regions being arranged alternately in a one-dimensional or two-dimensional periodic order across the surface of the first optical element, where the first refractive index is greater than the second refractive index over the entire wavelength range visible to the human eye. The optical element further includes a first layer on the light input side of each second region that is switchable between a permanently opaque or transparent state and an opaque state, and a second layer on the light output side of each second region that is switchable between a permanently opaque or transparent state and an opaque state.

[0015] Light impinging on the optical element on the light inlet side, based on the first layer, if the first layer is opaque, enters the optical element exclusively through the light inlet surface of the first region, where, depending on the angle of incidence, polarization, and the ratio of the first refractive index to the second refractive index, it either a) propagates unimpeded or is totally internally reflected within the first region and is then emitted again at the light outlet surface of the respective first region, or b) passes from the first region into an adjacent second region, propagating therein and finally being absorbed at the light outlet side if the second layer is opaque, or emitted if the second layer is transparent, or c) if the light passes from the first region into an adjacent second region, it again enters another adjacent first region and, depending on the given diffusion direction and polarization, is either emitted at the light outlet surface or propagates further within the optical element and is finally emitted or absorbed. Here, unimpeded propagation in case a) means that the light ray travels straight through the first region without encountering any region boundaries and without being totally internally reflected.

[0016] As a result, the light exiting the optical element on the light output side has a limited diffusion direction compared to the light impinging on the optical element on the light input side, provided that at least one of the layers, i.e. the first layer and / or the second layer, but preferably the second layer, is opaque.

[0017] The angle of incidence of a ray of light into the first region is a directional vector that represents the horizontal and vertical angles of incidence, particularly on the light-entering surface (also called the "bottom surface") of the first region, and, together with the polarization state, is very important for the further propagation of light at the interface with the first region B1 or the second region.

[0018] Basically, all rays that do not fall into case a) or b) should fall into case c).

[0019] The "periodic order" of the first and second regions does not mean that the regions must always have the same width and / or height, but simply that the first and second regions must alternate, although their sizes can vary.

[0020] The third case, c), occurs only when light from a first region enters an adjacent second region and then reenters another adjacent first region. That is, after crossing the refractive index boundary from the first region to the second region, the light again crosses the next refractive index boundary from the second region to the other adjacent first region, and depending on the given diffusion direction and polarization, either exits the light exit surface or propagates further within the optical element, ultimately exiting or being absorbed. This case is interesting for special applications, for example, when light diffusion directions with a central angle of approximately 30° to 50° are absorbed, but larger or smaller angular ranges are exposed to the light. Case c) can be included or excluded based on optical simulations of the optical element by appropriately dimensioning the first and second refractive indices and appropriately selecting the widths and heights of the first and second regions. This will be discussed in more detail below.

[0021] To achieve the preferred restriction of the direction of diffusion of incident light according to the invention (i.e., only rays of case a) it is important that the first and second layers are actually opaque: as soon as one of the layers is no longer opaque, oblique rays exceeding the inherent limiting angle of total internal reflection at the interface between the first and second regions can exit at the upper edge of the second region or, as the case may be, later when entering the second region, for example, through the upper edge, i.e., the exit surface of the first region B1.

[0022] An advantageous embodiment is configured such that each first layer provided on the light-emitting surface of the second region is formed by a permanent absorber layer and / or by at least one layer that specularly reflects away from the optical element. It goes without saying that if only one specularly reflecting layer is present within the scope of the invention, this layer also has opaque properties. Specular reflection properties contribute to increased efficiency, for example, if the optical element according to the invention is integrated into a lighting device, for example for an LCD panel.

[0023] Furthermore, each second layer on the light output surface of the second region can be formed by a permanent absorber layer. In certain static embodiments, when the first and second layers have permanent opaque properties and the first and second refractive indices do not change, the optical element acts to permanently restrict the direction of diffusion of incident light.

[0024] In a particular embodiment of the optical element according to the invention, the first refractive index (N1) of the material in the first region (B1) and / or the second refractive index (N2) of the material in the second region (B2) are switchable between at least two states, so that the ratio (N1, N2) of the two refractive indices at the boundary between the first region (B1) and the second region (B2) is respectively adjustable, thereby varying the said restriction in the diffusion direction.

[0025] In this regard, at least one of the materials of the first and / or second region can consist of a liquid crystal in contact with an electrode to induce a change in the refractive index for linearly polarized light in the liquid crystal via a change in voltage across the electrode. The electrodes, if arranged on the light exit and entrance surfaces, i.e., the upper and lower sides, of the first region, can be transparent, for example in the form of an ITO (indium tin oxide) layer. However, if electrodes are required to change the second refractive index of the second region, semi-transparent or even opaque electrodes can also be used, especially if the first and second layers are formed as permanent absorber layers.

[0026] In this liquid crystal embodiment, it is preferred that the first and second layers are permanently opaque, so that in principle only the light rays in case a) can exit the optical element upwards. However, these light rays in case a) will have a narrower or wider angular range in the direction of diffusion depending on the refractive index difference at the interface from the first region to the second region. This angular range is wider for larger refractive index differences and narrower for smaller refractive index differences.

[0027] On the other hand, in other switchable embodiments of the present invention, the property of restricting the direction of diffusion of light incident on the optical element can be switched on / off when the first and / or second layers are switched between an opaque and a transparent state. That is, the direction of light diffusion is restricted only when both layers are opaque (case a). As soon as one of the layers is no longer opaque, the restriction on the direction of light diffusion no longer exists (cases a), b), and possibly c). In this way, the optical element is switchable. Furthermore, when both layers are switched to transparent, the optical element simply causes ray shifting and total internal reflection—depending on the direction of light incidence—but does not block light as a whole.

[0028] In a preferred switchable embodiment, only the upper second layer is made switchable between opaque and transparent, while the lower first layer is made permanently opaque (and possibly reflective), which is sufficient to achieve the desired effect.

[0029] The switchability of both layers may preferably be based on one or more of the principles of electrowetting, electrophoresis, electrochromism and / or liquid crystal cells, although other embodiments are of course also possible.

[0030] In the case of electrowetting, at least two states of the liquid or liquid mixture to be electrowetted are defined for at least one of the layers: in a first operating state, the layer covers the corresponding surface of the second region as completely as possible and will therefore be opaque (in this case there is a restriction in the direction of diffusion, case a)); in a second operating state, the layer covers the corresponding surface of the second region with as little area as possible and will therefore be almost transparent (in this case there is no or negligible restriction in the direction of diffusion, cases a), b) and possibly c)).

[0031] In the case of electrophoresis, at least one of the layers will be provided with opaque particles capable of electrophoresis in a liquid or gel matrix. Under the action of an electric field that can be applied via transparent electrodes, these particles will cover the corresponding surface of the second region as completely as possible in a first operating state, resulting in the layer being opaque (in this case, there will be a restriction in the direction of diffusion). In a second operating state, with a different electric field distribution, the particles will cover the corresponding surface of the second region as small an area as possible in the layer, or will be transported into a reservoir or dispersed in the volume, resulting in the layer being transparent (in this case, there will be no restriction in the direction of diffusion).

[0032] Basically, this embodiment can be configured using electrophoresis such that, for at least one of both layers, in particular the second layer, the particles are located either directly above the second region or at a distance therefrom (up to 100 μm is sufficient) so that the total internal reflection structure at the surface of the second region is either disturbed (by a corresponding absorption of light by the particles) or not (by the particles being at a corresponding distance) and total reflection occurs, with the corresponding light rays, after further propagation within the optical element, at least partially exiting from the light exit surface of the first region. Generally, in this context, all optical switching techniques based on so-called "frustrated total internal reflection" or similar variants can be applied.

[0033] Further particles of interest include Janus particles that can rotate in place under the action of an electric field, with approximately half of their surface being opaque and the other half being scattering, white, and / or reflective. These Janus particles can be in either layer, and can switch these layers between an opaque state and a reflective state, in which the corresponding light ray is reflected and at least partially emitted from the light exit surface of the first region after further propagation within the optical element.

[0034] In the case of electrochromism, both layers may be made of electrochromic materials, such as certain metal oxides (TiO2, NiO, Nb2O, MoO3, Ta2O5, WO3, IrO2, Zr2O5), and corresponding transparent electrodes, such as ITO (indium tin oxide), FTO (fluorine tin oxide), or AZO (aluminum doped zinc oxide), in which the electrochromic material is embedded. Depending on the voltage applied to the electrodes, at least two states are defined for both layers: in a first operating state, the layer is opaque (in this case, there is a restriction in the direction of diffusion), and in a second operating state, the layer is transparent (in this case, there is no restriction in the direction of diffusion).

[0035] Both layers can be formed as a liquid crystal cell, e.g., a TN cell with a corresponding polarizer pair. In this case, both layers can be switched to opaque (in which case the diffusion direction is restricted) or transparent (in which case the diffusion direction is not restricted) as appropriate by applying a corresponding electric field or voltage to the electrodes. The polarizers of the polarizer pair can also physically correspond to the polarizers of an LCD panel when the optical element according to the present invention is used in combination with such an LCD panel.

[0036] Generally speaking, the smaller the difference between the first and second refractive indices, the narrower the light distribution of light exiting the optical element. For a clearer understanding of physics, it should be noted that "refractive index" refers to the first or second refractive index for a selected wavelength, e.g., 580 nm, or the respective dispersion curves across the entire wavelength range visible to the human eye. In the case of dispersion curves, the difference in refractive index refers to the respective value corresponding to the difference between the two refractive indices at the selected visible wavelength λ.

[0037] In this context, it should be noted that in a particular embodiment, the optical element can be designed as a very precise wavelength-selective color filter. That is, when the dispersion curves of both refractive indices intersect depending on the wavelength, in the case of an opaque layer, at wavelengths where the second refractive index is greater than the first refractive index, the corresponding wavelength range will be effectively eliminated and therefore not emitted from the optical element, while at wavelengths where the first refractive index is greater than the second refractive index, the corresponding wavelength range will be emitted from the optical element. Depending on the design of the dispersion curves, such an optical element with wavelength-selective effect will operate with obliquely directed light, since in any case, the limiting angle of total internal reflection at the interface between the first and second regions must be utilized to separate the spectra. In an exemplary development, such a wavelength-selective color filter would separate two spectra, for example, a narrow ultraviolet spectrum and a broad white spectrum. If the separation effect is eliminated by turning off the opacity of at least one of the layers, both spectra would be able to pass through the color filter. The ultraviolet light is then converted into visible white light, making it possible to switch between various angular spectra relative to the white light as a whole.

[0038] In an advantageous embodiment of the optical element, the first and second regions are arranged in alternating stripes across the surface of the optical element when viewed in parallel projection perpendicular to the optical element, so that the restriction of the light diffusion direction will be effective in a direction perpendicular to the stripes but not in a direction parallel to the stripes.

[0039] In contrast, in another embodiment, the first regions are arranged so that they are distributed in the form of dots, circles, ellipses, rectangles, hexagons, or other two-dimensional shapes across the entire surface of the optical element when viewed in parallel projection perpendicular to the optical element, and the second regions are shaped complementarily to each other. This ensures that the restriction of the light diffusion direction is effective in at least two planes perpendicular to the surface of the optical element. In practice, such an optical element essentially functions to focus the light diffusion direction of transmitted light at any angle close to or parallel to the central normal of the optical element. In this case, "close" means that the deviation from the central normal or parallel to it is less than 25° or 30°, depending on the embodiment.

[0040] Other shapes of the first and second regions are possible as well, but what is always important to maintain the functional form of the invention is that the first and second regions are optically directly adjacent to each other, providing an optical index jump with as little gap as possible.

[0041] In another embodiment, the first and second regions are trapezoidal in cross section perpendicular to the top surface of the optical element. This configuration of the first and second regions allows for precise influence of the direction of light diffusion from the optical element, i.e., for the light to be focused more or less strongly on the surface depending on the embodiment. Furthermore, for example, the cross-sectional shape of the first and second regions can be a parallelogram, which results in a shift in the vertex due to the corresponding inclination of the interface between the first and second regions. The trapezoid shape has the advantage that it allows for better focusing of the angular distribution, thus further improving the anti-spy mode.

[0042] Furthermore, it may be advantageous if the at least temporarily opaque first and / or second layer is embedded in the material constituting the first region, preferably with a seamless transition between the material portion of the first region of the optical element and the portion embedding the corresponding layer.

[0043] Furthermore, at least some, preferably all, of the first regions may have a lens structure, preferably a convex lens structure, applied to their light exit side, i.e., the upper side relative to the viewer. This helps to influence the direction of light diffusion from the optical element in a predetermined manner. Alternatively or additionally, the light entrance side of the first region, i.e., the lower side relative to the viewer, may be provided with a concave or convex lens structure to influence the direction of light entry into the first region and thereby influence whether the light ultimately falls into case a), b), or c).

[0044] In principle, within the scope of the present invention, the upper second layer and the lower first layer are interchangeable, i.e., the first optical element will function regardless of which major surface of the optical element is on top or bottom, especially if both layers are permanently opaque.

[0045] Furthermore, it may be useful to place a polarizer, optionally a reflective polarizer, below and / or above the optical element to optimize the effect. Controlling the polarization with a polarizer increases the efficiency of utilizing the refractive index transition. Furthermore, p-polarized light can be used for the incoming or outgoing light to minimize Fresnel reflections, i.e., to optimize the restriction of the light diffusion direction.

[0046] For special applications, at least one first region is formed on the optical element, the shortest extension of which, in a parallel projection perpendicular to the optical element, can be at least 20 times greater than the shortest extension of all second regions, in a parallel projection perpendicular to the optical element, and within said at least one first region, except for its edges and parallel displacement, the diffusion direction of light leaving the optical element on the light output side is unrestricted compared to light impinging on the optical element. This means that the restriction of the diffusion direction does not affect the entire surface of the optical element. Such unrestricted first regions can be repeated many times on the optical element without contacting each other.

[0047] Furthermore, in addition to the first and second regions, other regions having parameters different from those of the first and second regions in terms of shape and / or refractive index may be formed, and it may be meaningful for light passing through these other regions and exiting the optical element to be restricted in the diffusion direction differently from that of the first region. In this way, it is possible to distribute regions on the optical element that have different restrictions on the light diffusion direction, in other words, different focusing.

[0048] Furthermore, it is conceivable to provide the optical element with an additional reflector layer and / or an additional absorber layer in order to further strengthen or adjust the effect of limiting the light diffusion direction. Furthermore, it is also possible to apply a protective coating or substrate to the light entrance side and / or the light exit side, i.e., the upper and / or lower side of the optical element. However, the influence on the light ray displacement and light direction, especially when the light exits from the first region, should be taken into account in the technical optical dimensioning.

[0049] The present invention is of particular interest for the use of the optical element described above in conjunction with an image display device (e.g., LCD panel, OLED, microLED, or any other display technology) or in conjunction with an illumination device for a transmissive image display device (e.g., LCD panel). In the latter case, the optical element would be directly integrated into an illumination device for a transmissive image display device such as an LCD panel, particularly in a switchable configuration. This illumination device would permanently act as a directional backlight (if the first and second layers are permanently opaque) and could be used, for example, in embodiments according to the applicant's International Patent Application WO 2015 / 121398 or International Patent Application WO 2019 / 002496. Alternatively, such an illumination device comprising at least one surface emitter and an optical element according to the present invention could also function directly as a switchable illumination device for an LCD panel if at least one of the layers is switchable between a transparent mode and an opaque mode.

[0050] In the above-described method of use, switchable anti-peeping for the image display device is achieved. That is, in a first operating state in which only the above-described case a) remains for the light beams emitted from the optical element, an anti-peeping effect is provided according to a design having a top-hat distribution. In a second operating state in which the light beams emitted from the optical element generally fall into cases a) and b), and only in exceptional cases, case c) also falls into case a), a free-viewing mode is provided in which the image display device can be freely viewed from any direction.

[0051] When the optical element according to the present invention is placed in front of an image display device in the viewing direction to selectively or permanently restrict its light diffusion direction, there can optionally also be an optical system on the image display device that focuses the light emitted by each pixel of the image display device onto a surface located substantially opposite the first regions. This can be done, for example, by a microlens grid or lenticulars with a period of approximately the pixel width (or pixel height, as the case may be). The period of the first regions should in the best case coincide with the period of the pixel width or pixel height.

[0052] Such a screen comprising at least one optical element (also called first optical element) as described above and an image display device can be used, for example, in automobiles or mobile devices. Furthermore, in some cases, the first optical element, whether switchable or not, can be retrofitted to the image display device by being placed in front of the image display device.

[0053] The present invention also includes a method for manufacturing such a first optical element, which includes the following steps: First, a mold is manufactured having the positive structure of the desired first region and the negative structure of the support (i.e., the second region is filled with mold material, while the first region is not. A cavity for the support may be present in the mold, which will be filled in a subsequent step with a polymer specifically for the first region). Next, the mold is filled with a first polymer that is initially liquid and has a first refractive index after hardening. The first polymer is hardened by ultraviolet light or cooling, after which the workpiece is removed from the mold. Subsequently, the structure of the second region in the workpiece is filled with a second polymer that has a second refractive index after hardening. The second polymer is also hardened by ultraviolet light or cooling.

[0054] Optionally, after hardening of the first or second polymer, a second region of the surface, i.e., the top and bottom surfaces of the workpiece as viewed from the viewer, is vapor-deposited or sputtered through a mask protecting the first region with an opaque or transparent-to-opaque switchable material to obtain a first or second layer, or is printed with an opaque material.

[0055] The present invention further includes another method for manufacturing a (first) optical element, comprising the steps described below. First, a plurality of base blocks are prepared, each including layers bonded together in the order described herein: a second layer acting as an absorber layer, a second transparent layer made of a material having a second refractive index, an opaque first layer, and a first transparent layer made of a material having a first refractive index. Next, a plurality of base blocks are stacked and bonded one on top of the other to obtain a first laminated block. Disks having a second thickness are cut from the laminated block. These disks are then stacked and bonded with a first transparent layer, each having a first refractive index and a first thickness, between them to obtain a second laminated block. Subsequently, optical elements are cut from the second laminated block. Here, the first layers can be preferably formed to be reflective. The base blocks can be bonded to each other and / or the disks to the first transparent layer, for example, by vulcanization. Cutting the disks from the first laminated block and / or the optical elements from the second laminated block is preferably performed perpendicular to the extension plane of the individual layers.

[0056] In a particular embodiment of the optical element, the second transparent layer having the second refractive index may also be selected to be absorbing, in which case the second layer acting as an absorber layer may be omitted.

[0057] Other possible manufacturing alternatives include using two polymers to form the first and second regions B1 and B2, each with a different refractive index, in a 3D printing process, etching glass and then filling the etched regions (either the first or second regions) with a polymer, preferably in a subsequent process, differential cross-linking of polymers, and the use of photo-aligned molecules. In all cases, the first and second layers are further provided as described above. It goes without saying that other manufacturing processes for optical elements are also possible.

[0058] The object of the present invention is also achieved by a method for restricting the diffusion direction of light diffused over a surface in the wavelength range visible to the human eye, comprising the following steps: In a first step, the light is oriented over a surface by an area-like opening, which includes at least first transparent regions and second opaque regions arranged alternately in a one- or two-dimensional periodic order on the aperture surface. The light propagating through the first transparent region over the entire wavelength range is split angularly based on the refractive index into two light rays: those that are reflected within the limiting angle of total reflection at the refractive index boundary, i.e., at angles smaller than the limiting angle of total reflection, and are ultimately emitted, i.e., after one or more total reflections or unimpeded propagation, and those that are reflected outside the limiting angle of total reflection, i.e., at angles larger than the limiting angle of total reflection for this material combination, and are subsequently absorbed by an absorber. As a result, the emitted light has a more restricted diffusion direction than the light initially diffused over the surface.

[0059] The explanations in the description of the (first) optical element according to the invention in various embodiments shall apply mutatis mutandis here, and the above explanations shall apply mutatis mutandis here, whereby the first region and the second region may correspond to each other in the transferred sense, and for reasons of redundancy, a detailed description will not be given here.

[0060] The invention further includes an optical element consisting of a one- or two-dimensional periodic sequence of two transparent, complementary types, each with a different refractive index, optionally formed on a flat substrate, thereby forming a plane in each of two directions. In this case, the refractive index of one of the types can advantageously be equal to 1. That is, the material in one of the types is, for example, air. As a result, light impinging on such an optical element in a preferred direction is transmitted unimpeded, while light having an angle of more than 15° to the preferred direction is deflected by the optical element due to total internal reflection and / or Fresnel reflection. Here too, the diffusion direction of the emitted light is affected. The previously described embodiments are applicable mutatis mutandis and will not be repeated here.

[0061] Finally, the present invention further includes an optical element extending over a light-input and light-output surface. The optical element includes first regions made of a transparent material having at least a first refractive index and second regions made of an opaque material having a second refractive index, the regions alternating in a one- or two-dimensional periodic sequence across the surface of the optical element, with the first refractive index being greater than the second refractive index across the entire wavelength range visible to the human eye. Light impinging on the optical element at its first major surface enters the optical element exclusively through the light-input surface of the first region due to the opaque material of the second region. Depending on the geometric direction of incidence, polarization, and the ratio of the first and second refractive indices, a) the light propagates unimpeded or is totally internally reflected within the first region and then re-emitted at the light-output surface of the respective first region, or b) the light passes from the first region into an adjacent second region where it is absorbed due to the opaque material of the second region. In this case, the difference between the first and second refractive indices causes light rays entering the second region to be refracted more strongly away from normal, thereby improving absorption of such light compared to a material of the same refractive index. That is, such light rays are extinct better or more strongly than if there was no difference in refractive index. In doing so, light exiting the optical element at the second major surface of the optical element as a whole is limited in its direction of diffusion compared to light impinging on the optical element at the first major surface.

[0062] This embodiment improves upon the prior art in that, in particular, first, a top-hat distribution is achieved even with an optical element similar to a louver filter. This is because, due to total internal reflection, more useful light is transmitted within the desired limited angular range than in the prior art without total internal reflection. Second, the angular range of light transmitted through the third optical element is significantly more restricted. This is because not only do the opaque louvers affect the direction of light, but the refractive index difference between the two regions also causes light entering the second region to be refracted more strongly away from the normal, thereby requiring a longer optical path through the absorbing material and therefore being more extinct than would be the case without such a refractive index difference.

[0063] An opaque material with a second refractive index is so named because of its opaque effect. Specifically, it is a transparent material with a second refractive index that, when mixed with an absorbing material, especially absorbing particles, produces an overall opaque effect. In other words, an opaque material has both transparent and opaque portions. The transparent portion of the opaque material can be, for example, a lacquer or polymer, and the opaque portion can be mixed with, for example, graphite particles with a size of less than 500 nm in the direction of maximum extension, or black carbon nanoparticles, such as soot particles, with a size of less than 200 nm. Alternatively, or in combination, the opaque portion of the opaque material can contain a dye or dye mixture. A suitable dye is, for example, Sudan Black, which absorbs all light in the visible range. The mass fraction of absorbing particles in an opaque material should generally not exceed 50%, although exceptions are possible.

[0064] In a preferred embodiment, a third region made of another opaque material having a third refractive index is formed between each two second regions, the third refractive index being greater than the first refractive index and greater than the second refractive index. In this particular case, the difference in refractive index between the first and second refractive indexes should preferably not exceed 0.1, whereas a larger difference between the first and third refractive index is desirable for effectiveness. Furthermore, the second region can be formed between the light entrance surface of the optical element and the third region on the one hand, and between the light exit surface of the optical element and the light exit surface of the first region on the other hand. This further strengthens the convergence of the angle range in which the light is emitted, thereby improving the anti-spy mode.

[0065] In this case, the other opaque material having a third refractive index is constructed similarly to the opaque material having the second refractive index, i.e., it includes a transparent portion and an opaque portion with a mass fraction of absorbing particles of at most 50%. In this three-material embodiment, the mass fraction of absorbing particles in the opaque material having the second refractive index can be significantly lower than 50% if it is sufficiently high in the other opaque material having the third refractive index.

[0066] The optical element just described advantageously comprises a specular reflection on one of its major surfaces, preferably the lower major surface. This can be an angle-dependent specular reflection over the entire major surface, or a completely specular reflection at the surface of the second region. The explanations given in the introduction regarding the special embodiments of the optical element also apply to this optical element and will not be repeated.

[0067] In this regard, the present invention further includes a method for manufacturing the last-mentioned optical element, the method comprising the steps of: stacking alternating first layers of a transparent material having a first refractive index and second layers of an opaque material having a second refractive index, the first refractive index being greater than the second refractive index; bonding the first and second layers together, for example by vulcanization or adhesive bonding; and finally, cutting the optical element from the layer composite.

[0068] Generally, in all optical elements, the roughness R at the interface between regions of different refractive index is a should preferably be 20 nm or less.

[0069] The various embodiments of the present invention described above can also be implemented directly on a self-emissive image display device, where OLED panels, as described in more detail below, are particularly suitable, although other self-emissive display types are also contemplated.

[0070] For example, this can be achieved by forming a first region of a material having a first refractive index directly on the light-emitting area of ​​the OLED pixel. A second region having a structure complementary to the first region is formed in the non-light-emitting area of ​​the OLED panel. The second region is at least temporarily, i.e., permanently or switchably, covered with an opaque first and / or second layer. The first region is not covered with a scattering structure to increase light yield from the OLED pixel, but is preferably covered at least temporarily above the opaque first and second layers.

[0071] Essentially, the performance of the present invention is maintained if the above parameters are varied within certain limits.

[0072] It is obvious that the features mentioned above and those to be described below can be used not only in the combinations described, but also in other combinations or alone, without departing from the scope of the invention.

[0073] The present invention will now be described in detail by way of example embodiments with reference to the accompanying drawings, which also disclose essential features of the present invention. These example embodiments are merely illustrative and should not be construed as limiting the invention. For example, a description of an example embodiment having a large number of elements or components should not be construed as meaning that all of these elements or components are required for implementation. Rather, other example embodiments may include alternative, fewer, or additional elements or components. Elements or components of different example embodiments may be combined with one another unless otherwise specified. Modifications and variations described with respect to one example embodiment are also applicable to other example embodiments. To avoid redundancy, identical or corresponding elements in different figures will be given the same reference numerals and will not be described repeatedly. [Brief explanation of the drawings]

[0074] [Figure 1a] FIG. 1a is a principle diagram (cross-sectional view) of a first optical element in a first state in which only light rays in case a) are emitted from the optical element in the first embodiment.

[0075] [Figure 1b] FIG. 1b is a principle diagram (cross-sectional view) of the first optical element in the first embodiment in a second state in which only the light rays in cases a) and b) are emitted from the optical element.

[0076] [Figure 1c] FIG. 1c is a principle diagram (cross-sectional view) of the first optical element in the first embodiment in a third state in which the light ray is not absorbed but is merely displaced and / or totally reflected.

[0077] [Figure 1d] FIG. 1d is a principle diagram (cross-sectional view) of the first optical element in the second embodiment in a first state in which only the light rays in cases a) and c) are emitted from the optical element.

[0078] [Figure 2]Figure 2 shows the principle of the first and second regions of the optical element as seen on a parallel projection plane perpendicular to the optical element. These regions are arranged in alternating bands across the entire surface of the optical element.

[0079] [Figure 3a] Figure 3a is a diagram showing the principle of the first and second regions of the optical element as viewed on a parallel projection plane perpendicular to the optical element. The first regions are arranged in a rectangular shape distributed across the entire surface of the optical element and are completely surrounded by the second regions.

[0080] [Figure 3b] Figure 3b is a diagram showing the principle of the first to fourth regions of the optical element as viewed on a parallel projection plane perpendicular to the optical element, where the first, third, and fourth regions are distributed over the entire surface of the optical element and are completely surrounded by the second region.

[0081] [Figure 4] FIG. 4 is a diagram (cross-sectional view) illustrating the principle of the first optical element according to the third embodiment.

[0082] [Figure 5] FIG. 5 is a diagram (cross-sectional view) illustrating the principle of the first optical element according to the fourth embodiment.

[0083] [Figure 6a] FIG. 6a is a principle diagram (cross-sectional view) of a first optical element according to the fifth embodiment.

[0084] [Figure 6b] FIG. 6b is a principle diagram (cross-sectional view) of the first optical element in the sixth embodiment.

[0085] [Figure 6c] FIG. 6c is a principle diagram (cross-sectional view) of the first optical element in the seventh embodiment.

[0086] [Figure 7] FIG. 7 is a diagram (cross-sectional view) illustrating the principle of the first optical element according to the eighth embodiment.

[0087] [Figure 8] FIG. 8 shows simulated normalized luminance plotted against emission angle for three parameter sets for light emitted from the first optical element of the first embodiment.

[0088] [Figure 9] FIG. 9 is a plot of simulated normalized luminance versus emission angle for three other parameter sets for light emitted from the first optical element in the first embodiment, compared to a louver filter.

[0089] [Figure 10] FIG. 10 is a plot of simulated normalized luminance of three parameters versus emission angle for light emitted from the first optical element of the second embodiment.

[0090] [Figure 11] FIG. 11 is a diagram showing a simulation of the ratio of luminance outside the range of −25° to +25° for light emitted from the first optical element of the first embodiment.

[0091] [Figure 12] FIG. 12 is a principle diagram (cross-sectional view) of the first optical element in the ninth embodiment in a first state in which only light rays in case a) are emitted from the optical element within a narrow angle range.

[0092] [Figure 13] FIG. 13 is a principle diagram (cross-sectional view) of the first optical element in the ninth embodiment in a second state in which only the light rays of case a) exit the optical element in an expanded angular range compared to the situation in FIG.

[0093] [Figure 14] FIG. 14 is a principle diagram showing the method in which the regions C1 and C2 are arranged so as to be alternately distributed in bands.

[0094] [Figure 15] FIG. 15 is a diagram (cross-sectional view) illustrating the principle of the second optical element in the first embodiment.

[0095] [Figure 16] FIG. 16 is a diagram (cross-sectional view) illustrating the principle of the second optical element in the first embodiment, with exemplary light rays drawn thereon.

[0096] [Figure 17] FIG. 17 is a diagram illustrating the principle of the first optical element according to the tenth embodiment.

[0097] [Figure 18] FIG. 18 is a plot of a comparison of simulated normalized luminance of light emitted from the first optical element of the first and eighth embodiments versus emission angle.

[0098] [Figure 19] FIG. 19 is a plot of a simulated comparison of normalized luminance versus emission angle for light emitted from the first optical element of the ninth embodiment in two states.

[0099] [Figure 20] FIG. 20 is a principle diagram (cross-sectional view) of a first state when the first optical element in the first embodiment is used in combination with a transmissive image display device and a backlight.

[0100] [Figure 21] FIG. 21 is a principle diagram (cross-sectional view) of the first optical element in the first state when used together with the self-illuminating image display device in the first embodiment.

[0101] [Figure 22] FIG. 22 is a diagram (partial view) showing an eleventh embodiment in which the first optical element of the first embodiment is switchable.

[0102] [Figure 23]FIG. 23 is a diagram (partial view) showing a first state in which the first optical element of the first embodiment is expanded to a switchable twelfth embodiment.

[0103] [Figure 24] FIG. 24 is a diagram (partial view) showing a second state in which the first optical element of the first embodiment is developed into a switchable twelfth embodiment.

[0104] [Figure 25a] FIG. 25a is a principle diagram illustrating a method for manufacturing the first optical element. [Figures 25b-25c] 25b and 25c are diagrams illustrating the principle of a method for manufacturing the first optical element. [Figure 25d] FIG. 25d is a principle diagram illustrating a method for manufacturing the first optical element. [Figure 25e] FIG. 25e is a principle diagram illustrating a method for manufacturing the first optical element. [Figure 25f] FIG. 25f is a principle diagram illustrating a method for manufacturing the first optical element.

[0105] [Figure 26] FIG. 26 is a diagram illustrating the principle of the third optical element.

[0106] [Figure 27a] FIG. 27a shows an embodiment of the third optical element in the developed example. [Figure 27b] FIG. 27b shows an embodiment of the third optical element in the developed example. [Figure 27c] FIG. 27c shows an embodiment of the third optical element in the developed example.

[0107] [Figure 28] FIG. 28 is a diagram showing another embodiment of the third optical element.

[0108] [Figure 29] FIG. 29 is a diagram showing the ray transition for various incident conditions.

[0109] [Figure 30] FIG. 30 shows the angular range of transmitted light compared to incident light. DETAILED DESCRIPTION OF THE INVENTION

[0110] The drawings are not to scale and are merely diagrams of the principle. In reality, many rays exist, but only a few rays are shown for ease of viewing.

[0111] An exemplary planar first optical element 1 includes first regions B1 made of a first transparent material having at least a first refractive index N1 and second regions B2 made of a second transparent material having a second refractive index N2, the regions being arranged alternately in a one- or two-dimensional periodic order across the entire surface of the first optical element 1, with the first refractive index N1 being greater than the second refractive index N2 across the entire wavelength range visible to the human eye. The first optical element 1 further includes at least temporarily opaque first layers OB disposed below each of the second regions B2 and at least temporarily opaque second layers AB disposed above each of the second regions B2. Here, "at least temporarily" means that the layers are either permanently opaque or switchable between an opaque and a transparent state. The layers do not necessarily need to be switchable, so long as they are permanently opaque. The "upper side" generally refers to the light-emitting surface of the optical element 1, specifically the light-emitting surface of the first or second region. Similarly, the lower side corresponds to the light entrance side of the optical element 1, specifically the light entrance surface of the first or second region here. A viewer or user of the optical element looks at the upper side from which light of the element emerges.

[0112] Light impinging on the optical element 1 on the light input side, depending on the first layer OB and if this first layer OB is in an opaque state, will enter the optical element 1 exclusively through the light input surface of the first region B1, where, depending on the angle of incidence, polarization and the ratio of the first refractive index N1 to the second refractive index N2, it will either a) be totally internally reflected or propagate unimpeded within the first region B1 and then be emitted again at the light output surface of the respective first region B1, or b) pass from the first region B1 into the adjacent second region B2, propagate therein and finally be absorbed at the light output side if the second layer AB is in an opaque state or be emitted if the second layer AB is in a transparent state, or c) if the light has entered the adjacent second region (B2) from the first region (B1), it will again enter another adjacent first region (B1) and there, depending on the given diffusion direction and polarization, will be emitted at the light output surface or will propagate further within the optical element (1) and finally be emitted or absorbed. Finally, the light exiting the optical element (1) on the light output side is limited in its diffusion direction compared to the light impinging on the optical element (1) on the light input side. Essentially, all light rays that do not fall into case a) or b) should fall into case c). In reality, there are many first regions B1 and second regions B2 on the first optical element 1.

[0113] In this regard, FIG. 1a shows a principle diagram of such a first optical element 1 in a first embodiment in a first state (i.e., the first and second layers OB and AB are opaque) in which only light rays of case a) are emitted from the optical element 1. These light rays are limited in their diffusion direction compared to light rays entering the optical element 1 from below. The light rays of case b) described above are absorbed in the second layer AB. Light entering the first layer OB from below is also absorbed. For dimensioning purposes, D1 denotes the width of the first region B1, D2 denotes the width of the second region B2, and H denotes the equal height of both regions B1 and B2, respectively. In particular applications, the first region B1 and the second region B2 can also differ in height within certain limits.

[0114] Furthermore, Figure 1b shows a principle diagram of the first optical element 1 in the first embodiment in a second state, in which only light rays of cases a) and b) are emitted from the optical element 1. In this case, the upper second layer AB is in a transparent state (shown by the dashed line). The angular spectrum of light emitting from the optical element 1 at the upper side is therefore significantly broader than in the situation in Figure 1a, in which only light rays of case a) are emitted.

[0115] 1c shows a principle diagram of the first optical element 1 in the first embodiment in a third state in which no light rays are absorbed but only displacement and / or total reflection occurs, for which both layers AB and OB are in a transparent state (shown by dashed lines).

[0116] Finally, FIG. 1d shows a principle diagram of the first optical element 1 in the second embodiment in a first state (i.e., both layers AB and OB are opaque) in which only the light rays in cases a) and c) exit the optical element 1. A third case, c), for this light ray, i.e., after crossing the refractive index boundary from B1 to B2, crosses the next refractive index boundary to the next adjacent B1, where it is either exited or propagates further within the optical element, depending on the given diffusion direction and polarization, and is finally either exited or absorbed, is of interest for certain applications, for example, when light diffusion directions within a central angle range of approximately 30° to 50° are absorbed, but angles larger or smaller than this are irradiated. The case listed in c) can be included or excluded based on optical simulations of the optical element by appropriately dimensioning the first refractive index N1 and the second refractive index N2, as well as by appropriately selecting the widths and heights of the first and second regions B1 and B2.

[0117] To achieve a favorable restriction of the direction of diffusion of the incident light (i.e., only case a) of the light rays as shown in FIG. 1a still exists), it is important that both the first and second layers OB and AB, which are at least temporarily opaque, are actually opaque. As soon as one of these layers, for example the second layer AB, ceases to be opaque, oblique light rays which enter the second region B2 beyond the practical limiting angle of total internal reflection at the B1-B2 interface can inadvertently exit the upper edge of the interface through the non-opaque second layer AB.

[0118] 2 shows a principle diagram (i.e., a plan view) of the first region B1 and the second region B2 of the first optical element 1 as viewed in parallel projection perpendicular to the optical element 1, and these regions are arranged in strips so as to be alternately distributed across the entire surface of the optical element 1. This will result in the restriction of the light diffusion direction being effective in the direction perpendicular to the strip-shaped first region B1 and second region B2, but not in the direction parallel to these.

[0119] Alternatively, FIG. 3a shows a principle diagram (also a plan view) of the first and second regions B1 and B2 of the first optical element 1 in a parallel projection perpendicular to the optical element 1. Here, the first region B1 is arranged in a rectangular shape distributed over the entire surface of the optical element 1 and is completely surrounded by a single second region B2 (shown in black in the figure). That is, the second region B2 is shaped complementary to the first region B1. This allows the restriction of the light diffusion direction to be effective in at least two planes perpendicular to the surface of the optical element 1. In practice, the operation of such an optical element 1 is such that the light diffusion direction is focused at any angle close to or parallel to the central normal of the optical element. In this case, "close" means that the deviation from the central normal or parallel line is less than 25° or 30° (depending on the embodiment).

[0120] Furthermore, Figure 3b shows a principle diagram of multiple regions B1-B4 of optical element 1 as viewed in parallel projection perpendicular to the optical element. Regions B1, B3, and B4 are arranged in a rectangular shape across the entire surface of the optical element and are completely surrounded by region B2. In addition to the first region B1 and the second region B2, this optical element 1 also has additional regions B3 and B4. In this case, regions B1, B3, and B4 have different parameters regarding shape and / or refractive index. Therefore, light passing through these regions B3 and B4 and exiting the optical element 1 is restricted in the diffusion direction differently from region B1. In this way, it is possible to achieve a distribution of regions with different restrictions on the light diffusion direction, or in other words, regions with different focusing, across the entire optical element 1. All of the variations shown in Figures 2, 3a, and 3b can be appropriately combined with the situations shown in Figures 1a-1d. Other shapes of the first region B1 and the second region B2 are also possible. In this case, what is always important to maintain the functional form of the invention is that the first region B1 and the second region B2 are directly adjacent optically and are provided with an optical refractive index jump as close as possible to the gap.

[0121] In a preferred embodiment, the lower side of each at least temporarily opaque first layer OB, i.e., the light entrance surface of the second region B2, is formed by a permanent absorber layer and / or at least one lower specular reflective layer. Of course, if only one specular reflective layer is present, this layer also has opaque properties. The specular reflective properties contribute to increased efficiency, for example, when the optical element according to the present invention is incorporated into a lighting device, e.g., for an LCD panel. Furthermore, the upper side of each at least temporarily opaque second layer AB, i.e., the light exit surface of the second region B2, can also be formed by a permanent absorber layer. In this case, if both layers have permanent opaque properties and the first and second refractive indices N1 and N2 are unchanged in certain static embodiments, the optical element 1 permanently restricts the diffusion direction of the incident light. In some static embodiments, if both layers have permanent opaque properties and the first and second refractive indices N1 and N2 are unchanged, the optical element 1 permanently restricts the diffusion direction of the incident light.

[0122] In contrast, in another switchable embodiment of the present invention, at least one of the layers AB and / or OB of the first optical element 1 can be switched between an opaque and a transparent state, so that the property of restricting the diffusion direction of light incident on the optical element 1 can be turned on and off in this way. That is, the restriction is only present when both layers AB and OB are opaque (case a), see FIG. 1). As soon as one of the layers AB or OB is no longer opaque, the restriction on the light diffusion direction is removed (cases a) and b), and possibly c), as shown in FIG. 1b, among others. In this way, the optical element 1 is switchable. Furthermore, as shown in FIG. 1c, when both layers AB and OB are switched to transparent, the optical element 1 simply causes light ray displacement and redirection due to total internal reflection at the boundary between the first and second regions B1 and B2 depending on the direction of light incidence, but does not block light as a whole.

[0123] In a preferred switchable embodiment, only the upper second layer AB is designed to be switchable between opaque and transparent, while the lower first layer OB is configured to be permanently opaque (and possibly reflective), which is sufficient to achieve the desired effect.

[0124] The switchability of the first layer OB or the second layer AB can be preferably based on one or more of the principles of electrowetting, electrophoresis, electrochromism and / or liquid crystal cells. In the case of electrowetting, at least two states of the opaque liquid volume to be electrowetted for the first layer OB and / or the second layer AB will be defined. In this regard, FIG. 23 shows a partial view of a development of the first optical element 1 of the first embodiment into a switchable twelfth embodiment, here in a first state corresponding to FIG. 1a. In contrast, FIG. 24 shows a partial view of a development of the first optical element 1 of the first embodiment into a switchable twelfth embodiment, here in a first state corresponding to FIG. 1b. In the embodiments according to both FIGS. 23 and 24, at least the following components are present: That is, at least one flat indium tin oxide (ITO) electrode 4, a flat insulator layer 8, thin electrodes 9a protruding from the surface and each extending into the droplet 10, a controllable voltage source (not shown) in contact with the flat ITO electrode 4 and the flat electrode 9, and an opaque droplet 10 disposed between the insulator layer 8 and the electrode 9, possibly embedded in a gel matrix or transparent liquid, and subject to the electrowetting effect.

[0125] In a first operating state according to Fig. 23, the droplets 10 of the second layer AB will cover the corresponding surfaces of the second regions B2 as completely as possible and will therefore be opaque (in this case there will be a restriction in the direction of diffusion). In a second operating state according to Fig. 24, the droplets 10 of the second layer AB will cover the corresponding surfaces of the second regions B2 with as little area as possible and will therefore be almost transparent (in this case there will be no restriction in the direction of diffusion). In this respect, the voltage sources will be adjusted to the voltages required for the respective above states.

[0126] In the case of electrophoresis, the first layer OB and / or the second layer AB may be provided with opaque particles capable of electrophoresis in a liquid or gel matrix. Under the action of an electric field that can be applied via transparent electrodes, these particles will, in a first operating state, cover as completely as possible the surface of the second region B2 as the first layer OB or second layer AB, so that the layer OB or AB will behave opaquely (in this case, there will be a restriction in the direction of diffusion). In a second operating state, with a different electric field distribution, the particles will cover as little as possible the surface of the second region B2 as the first layer OB or second layer AB, or will be transported into a reservoir or dispersed in the volume, so that the layer will be transparent (in this case, there will be no restriction in the direction of diffusion).

[0127] In this variant, it is also possible for opaque, electrophoretically movable particles to replace both layers OB and / or AB. Such particles would either be on the surface of the second region B2, i.e., at the location of both layers OB and / or AB, preventing total internal reflection and creating an opaque state, or would be located up to 100 μm away after electrophoresis and allowing total internal reflection at said locations, thereby causing the light to propagate further within the optical element and finally be emitted in the first region B1.

[0128] 22 further reproduces a switchable development of the first optical element 1 into an eleventh embodiment as a partial view of the first embodiment. In this case, at least the following are present to form the second layer AB: transparent electrodes 4 and 6, a controllable voltage source (not shown) in contact with the transparent electrodes 4 and 6, at least one electrochromic layer 5, and an optional protective layer 7, such as glass or a polymer. In the case of electrochromism, the layer 5 may be formed by an electrochromic material, such as a metal oxide (TiO2, NiO, Nb2O, MoO3, Ta2O5, WO3, IrO2, or Zr2O5), and corresponding transparent electrodes 4, 6, such as ITO (indium-doped tin oxide), FTO (fluorine-doped tin oxide), or AZO (aluminum-doped zinc oxide), into which the electrochromic material is embedded. For the electrochromic layer 5, and thus for the second layer AB, at least two states are defined depending on the voltage applied to the electrodes 4, 6. In the first operating state, the second layer AB is opaque (in this case there is a restriction in the direction of diffusion), and in the second operating state, the second layer AB is transparent (in this case there is no restriction in the direction of diffusion). This also applies mutatis mutandis to the first layer OB.

[0129] The first layer OB and / or the second layer AB can also be formed as a liquid crystal cell, for example as a TN cell (twisted nematic liquid crystal cell) with a corresponding polarizer pair, which can be switched to opaque (in which case the diffusion direction is restricted) or transparent (in which case the diffusion direction is not restricted) by applying a corresponding electric field or voltage to the electrodes.

[0130] Furthermore, it may be advantageous if the first layer OB and / or the second layer AB are embedded in the material constituting the first region B1. In this case, the material portion of the first region B1 of the optical element 1 preferably seamlessly transitions into the portion in which the layer is embedded. In this regard, FIG. 4 shows a principle diagram of a first optical element according to a third embodiment, and FIG. 5 shows a principle diagram of a first optical element according to a fourth embodiment. Here, the material of the first region B1 having the first refractive index N1 can be the same material as the material of the substrate formed as described above, as shown in FIG. 4. Alternatively, it is conceivable that the second region B2 is completely surrounded by the material of the first region B1 having the first refractive index N1, as reproduced in FIG. 5.

[0131] In another embodiment, the first region B1 and the second region B2 are formed in a trapezoidal shape when viewed in a cross section perpendicular to the upper side of the optical element 1. In this regard, FIGS. 6A to 6C show principle diagrams of the first optical element 1 in the fifth, sixth, and seventh embodiments. Such embodiments of the first region B1 and the second region B2 allow for precise influence of the diffusion direction of light emitted from the optical element 1. That is, depending on the embodiment, stronger (FIG. 6a) or weaker (FIG. 6b) focusing of light is achieved on the surface. Furthermore, for example, by using a parallelogram-shaped cross section of the first region B1 and the second region B2 (FIG. 6c), the boundary surface between the first and second regions can be tilted, thereby achieving a shift in the vertex.

[0132] Furthermore, at least some, and preferably all, of the first regions B1 of the optical element 1 can be provided with a lens structure L, preferably a convex lens structure, on their upper side, i.e., light exit surface. This helps to influence the diffusion direction of light exiting the optical element 1 in a predetermined manner. In this regard, FIG. 7 shows a principle diagram of the first optical element 1 in an eighth embodiment. Alternatively or additionally, the lower side, i.e., the light entrance surface of the first region, can be provided with a concave or convex lens structure (not shown) to influence the light entrance direction into the first region and thereby influence whether the light ultimately falls into the above-mentioned case a), b), or c). The terms "upper side" and "lower side" are used relative to the viewer. The optical element is mounted in an image display device for the viewer, and the viewer perceives only the side of the first optical element 1 facing the viewer, i.e., the light exit side, which constitutes the upper side.

[0133] FIG. 8 shows simulated normalized luminance versus emission angle for three parameter sets for light emitted from the first optical element 1 of the first embodiment. This was based on the situation shown in FIGS. 1a and 2. 100% opacity of the first and second layers OB and AB was assumed. It is very clear that a top-hat profile is achieved with a small refractive index difference of 0.01 between N1 = 1.6 and N2 = 1.59. Furthermore, it is clear that extinction can be achieved at larger angles with any magnitude of coefficient. In this calculation example, the heights H of the first and second regions B1 and B2 are the same but varied between 32 μm, 50 μm, and 65 μm. The larger the height H, the narrower the angular range of the emitted light. All emitted light falls into case a).

[0134] The mechanism of action is as follows: When a ray of light strikes the interface between the first and second regions B1 and B2 (i.e., the interface between the first and second refractive indices N1 and N2), the ray is either totally reflected or refracted into the second region B2 (refractive index N2) depending on the angle of incidence. If the latter ray of light is refracted into the second region B2 (second refractive index N2), a (small) portion of the ray is nevertheless reflected back to the first region B1 (Fresnel reflection). The smaller the difference in refractive indices N1-N2, the smaller this reflected portion becomes. The higher the height H (constrained by manufacturing) is, the more this reflection effect is masked. Ideally, a nearly perfect rectangular distribution is obtained.

[0135] The drawings in Figures 8 to 10 already include the above reflections. Please note the logarithmic coordinates in these drawings. All of Figures 8 to 10 provide exemplary parameters for technical optical dimensioning of important parameters, namely, the width D1 of the first region, the width D2 of the second region, the identical height H of each region, the first refractive index N1, and the second refractive index N2.

[0136] Additionally, Figure 9 shows simulations of normalized luminance for light emitted from the first optical element 1 of the first embodiment under the same assumptions for three different parameter sets. This time, the height H = 65 μm is constant, and the second refractive index N2, and therefore the difference between the first refractive index N1 = 1.6 and the second refractive index N2, is varied (N2 = 1.56 / 1.575 / 1.59). It is clear that the larger the difference in refractive index, the more light is allowed at lateral angles. All emitted light is classified as case a). Nevertheless, a top-hat distribution is again provided. Figure 9 also includes a comparison with a conventional louver filter for restricting the direction of light. It is clearly visible that the first optical element 1 of the present invention has significantly improved characteristics compared to the prior art, i.e., louver filters. On the one hand, the anti-spying effect is significantly better from angles between 25° and approximately 30°, depending on the design. On the other hand, the present invention has a desirable top-hat distribution. In contrast, with louver filters that do not, as a rule, have a top-hat distribution, the perceptible luminance varies depending on the design and viewing position even when the filter is shifted by just a few degrees from the central perpendicular. When measured from an angle of 10 degrees or more from the central perpendicular, the perceptible luminance can drop dramatically to half.

[0137] In contrast, Figure 10 shows a plot of simulated normalized luminance for parameter sets versus emission angle for light emitted from the first optical element 1 of the second embodiment. Here, a burst-type distribution of light diffusion angles with edges on both sides can be clearly seen. While light classified as case a) is at angles between approximately -28° and +28°, additional light rays in case c) are at angles between approximately -50° and -77° and +50° and +77°.

[0138] Furthermore, FIG. 11 shows a simulation of the proportion of brightness outside the range of −25 to +25 degrees (i.e., light for case a) for light emitted from the first optical element 1 of the first embodiment. The first and second refractive indices on which this simulation is based are N1=1.6 and N2=1.59. In the upper (bright) parameter window, it can be seen that the proportion of light emitted in the above angular range is greatest. From this, a person skilled in the art can derive values ​​for setting the dimensions of the widths D1 and D2 and the height H of the first and second regions B1 and B2 to optimize the optical element 1 for case a).

[0139] 18 compares the simulation of normalized luminance versus emission angle for light emitted from the first optical element 1 of the first embodiment (corresponding to FIG. 1a) and the eighth embodiment (corresponding to FIG. 7). It can be seen that the angle limiting effect can be significantly improved by using the lens L without destroying the top-hat distribution.

[0140] In a particular embodiment of the optical element 1 according to the present invention, the first refractive index N1 of the material in the first region B1 and / or the second refractive index N2 of the material in the second region B2 can be switched between at least two states, thereby adjusting the refractive index difference at the region and refractive index boundary B1-B2, respectively, and thereby changing the diffusion direction restriction. In this regard, Figure 12 shows the logic of the first optical element 1 in the ninth embodiment in a first state in which only light rays in case a) are emitted from the optical element 1 within a narrow angular range. Here, the second refractive index N2 = 1.49 and the first refractive index N1 = 1.5 at the corresponding orientation of the liquid crystal.

[0141] FIG. 13 shows a principle diagram of the first optical element 1 of the ninth embodiment in a second state, in which only the light rays of case a) are also emitted from the optical element 1, but in an expanded angular range compared to the situation in FIG. 12. Here, the second refractive index N2=1.49 and the first refractive index N1=1.6 at the corresponding orientation of the liquid crystal. In this regard, FIG. 19 compares optical simulations of the normalized luminance versus the emission angle for light emitted from the first optical element 1 of the ninth embodiment in two states corresponding to FIGS. 12 and 13. It is clear that the switchable ninth embodiment of the optical element 1 described above allows for a change in the angular limit.

[0142] In the above-described ninth embodiment, at least one of the materials in the first region B1 and / or the second region B2 consists of a liquid crystal in contact with an electrode, and a change in the refractive index for linearly polarized light can be induced in the liquid crystal by varying the voltage at the electrode. The electrodes can be transparent, for example, in the form of an ITO layer, if they are located, for example, above and below the first region B1, i.e., on the light exit and light entrance surfaces. It should be noted that the first layer OB and the second layer AB are preferably permanently opaque, and in principle, only light rays in case a) can exit the optical element 1 upward. However, these light rays in case a) have a narrower or wider angular range of diffusion direction depending on the refractive index difference at the interface from the first region B1 to the second region B2, as shown in Figures 12, 13, and 19. This angular range is wider for larger refractive index differences and narrower for smaller refractive index differences. Essentially, this ninth embodiment can also have third, fourth, and further states corresponding to other refractive index values, if required for the application.

[0143] In a specific application example, at least one first region B1 is formed on the optical element 1, and the shortest extension of the first region B1, as viewed in a parallel projection perpendicular to the optical element 1, is at least 20 times greater than the shortest extension of all second regions B2, as viewed in a parallel projection perpendicular to the optical element 1. Within the at least one first region B1, the diffusion direction of light exiting the optical element 1 is unrestricted compared to light impinging on the optical element 1, except for its edges and parallel displacement. In this regard, FIG. 17 shows a principle diagram illustrating a first optical element 1 according to a tenth embodiment. The unshaded left half corresponds to a single, complete first region B1, while the shaded right half has alternating first regions B1 and second regions B2, corresponding to, for example, the first to ninth embodiments of the optical element 1. This means that the restriction on the diffusion direction of light passing through the optical element 1 does not affect the entire surface of the optical element 1, but only the right half in this example.

[0144] The present invention is particularly relevant when the above-described first optical element 1 is used in conjunction with an image display device (e.g., an LCD panel, OLED, or microLED, or other display technology) or with an illumination device for a transmissive image display device. In this regard, FIG. 20 reproduces a principle diagram (partial cross-section) of the first optical element 1 in the first embodiment in a first state and in conjunction with a transmissive image display device ("LCD") and a backlight ("BLU"). In particular, in a switchable embodiment, the optical element 1 is directly integrated into a backlight (BLU) for a transmissive image display device, such as an LCD module. Here, the permanently opaque layer OB is preferably reflective on the underside, so that light impinging thereon is reflected back to the backlight (BLU) and recycled there, as shown diagrammatically in the drawing. Thus, light from the backlight (BLU) can enter exclusively the first region (B1) and, when the second layer (AB) is opaque, experiences the light direction restriction of the present invention in the first state of the optical element 1. The image display device LCD is transmitted only by light directed in accordance with the present invention and is viewable only from a correspondingly limited range of angles, excluding, for example, scattering losses due to the LCD panel itself. Although not shown in the drawings, when the second state of the optical element 1 is set and the second layer AB is switched to transparent, a wide angular spectrum of light will be transmitted through the image display device LCD and will be viewable from a wide range of angles.

[0145] The above-described usage method achieves switchable anti-spying for the image display device LCD. Specifically, in the first operating state, where only the above-described case a) remains for the light beams exiting the optical element 1, the anti-spying effect is provided according to the design with a top-hat distribution. A top-hat distribution is more comfortable for the viewer than a typical light distribution based on a louver filter. This is because a louver filter significantly restricts freedom of movement, resulting in a noticeable and strong brightness drop even when moving the head sideways by a few centimeters (see also Figure 9 for comparison). If the screen size is large enough, a visible brightness drop occurs in some areas even when the head is not moving. This is effectively addressed by the top-hat distribution. In the second operating state, where the light beams exiting the optical element 1 generally fall into cases a) and b), and possibly also c), a free-viewing mode is provided, allowing the image display device LCD to be viewed freely from any direction.

[0146] Furthermore, FIG. 21 shows a principle diagram (partial cross-section) of the first optical element 1 in the first embodiment, in a first state and in use with a self-luminous image display device 3. In this case, the optical element 1 is arranged in front of such an image display device 3, for example, an OLED panel (although a backlit LCD panel or any other screen technology would also be applicable), in the viewing direction, and can selectively or permanently limit its light diffusion direction. In this case, an optical system may also be present on the image display device 3, focusing the light emitted by each pixel of the image display device 3 onto a surface located substantially opposite the first region B1. This is possible, for example, by a microlens grid or lenticular element having a period approximately equal to the pixel width (or pixel height, as the case may be). The period of the first regions B1 (i.e., the sum of the widths D2+D1) is aligned with each other, in the best case, matching the period of the pixel width or pixel height. In FIG. 21, the period of the pixel width of the image display device 3 is schematically indicated by two dashed lines. In this case, the pixels are approximately centered relative to the first region B1. For clarity, FIG. 21 does not include the optical system described above with a microlens grid or lenticulars, but it may be present.

[0147] The present invention also includes a method for manufacturing the first optical element 1, which will be described with reference to the simplified principle diagrams of FIGS. 25a to 25f. This method includes the following steps: First, a plurality of base blocks BL are fabricated (see FIG. 25a), each of which includes the following layers bonded together in the following order: a second layer AB acting as an absorber layer, a second transparent layer made of a material with a second refractive index N2, an opaque, optionally simultaneously reflective, first layer OB, and a first transparent layer made of a material with a first refractive index N1. Next, a plurality of base blocks BL are stacked and bonded one on top of the other to obtain a first laminated block ST (see FIG. 25b). From this laminated block ST, a disk having a second layer thickness D2 is cut, preferably perpendicular to the extension plane of each second layer AB (see FIG. 25c). Instead of a perpendicular cut, a cutting angle of approximately 60° to 120° can also be considered. The discs SC are then stacked with first transparent layers sandwiched between them, each having a first refractive index N1 and a first layer thickness D1, and joined together, for example by vulcanization or bonding, to obtain a second laminated block SN (see FIG. 25d). Finally, optical elements 1 are cut out of the second laminated block SN, preferably perpendicular to the extension plane of the individual discs SC (see FIG. 25e). This results in a (first) optical element 1 as shown in FIG. 25f. It goes without saying that other methods for manufacturing the optical element 1 are also possible.

[0148] FIG. 15 shows a second optical element 2 consisting of a one- or two-dimensional periodic sequence of two transparent complementary moulds, each having a first region B1 and a second region B2 with a first refractive index N1 and a second refractive index N2, respectively. These moulds are optionally formed on a flat substrate S, thereby forming a plane in each of the two directions. In this case, the second refractive index B2 can advantageously be equal to 1. That is, the material within the moulds in the second region B2 is, for example, air. This is shown in FIG. 15 as a principle diagram of the second optical element 2 in the first embodiment. FIG. 16 shows an exemplary light path for this. Light striking such a second optical element 2 in a preferred direction (at a narrow angle) is transmitted unimpeded (see the preferred direction, i.e., the normally incident light ray on the right). On the other hand, light at an angle of 15° or more relative to the preferred direction (see the oblique light ray on the left) is deflected by the second optical element 2 due to total internal reflection and / or Fresnel reflection. Here, too, the diffusion direction of the outgoing light is affected. The previously described embodiments may be applied mutatis mutandis and will therefore not be repeated here. The variants and means-and-action relationships of the previously described embodiments may be applied mutatis mutandis and will therefore not be repeated here for reasons of redundancy.

[0149] Finally, the present invention also includes a third optical element 10, which has a planar surface and a light entrance side and a light exit side, the principle diagram of which is shown in FIG. 26 (partial cross-section). It comprises first regions E1 made of a transparent material having at least a first refractive index N1 and second regions E2 made of an opaque material having a second refractive index N2, which are arranged alternately in a one- or two-dimensional periodic sequence across the entire surface of the optical element 10, with the first refractive index N1 being greater than the second refractive index N2 across the entire wavelength range visible to the human eye. Light impinging on the first major surface of the optical element 10 enters the optical element 10 exclusively through the light entrance surface of the first region E1 due to the opaque material of the second region E2. Depending on the geometric direction of incidence, polarization, and the ratio of the first refractive index N1 to the second refractive index N2, a) the light propagates unimpeded within the first region E1 or is totally internally reflected. In either case, the light is then re-emitted from the light exit surface of each first region E1. Alternatively, b) the light passes from the first region E1 into the adjacent second region E2 where it is absorbed due to the opaque material of the second region E2.

[0150] In this case, because the first refractive index N1 and the second refractive index N2 are different, light rays entering the second region E2 are refracted more strongly away from the normal. This limits the direction of diffusion of light exiting the second major surface of the optical element 10 compared to light impinging on the first major surface of the optical element 10. The opaque material having the second refractive index has a transparent portion assigned the second refractive index and an opaque portion made of absorbing particles. These particles are preferably uniformly distributed in the opaque material, and their mass fraction in the opaque material does not exceed 50%.

[0151] This third optical element 10 offers several improvements over the prior art, particularly in the following respects: First, a top-hat distribution is achieved with a third optical element similar to a louver filter because, due to total internal reflection, more useful light is transmitted within the desired limited angular range than would be the case without total internal reflection, as is typical in the prior art. Second, the angular range of light transmitted through third optical element 10 is significantly more restricted. This is because not only do the opaque louvers act to restrict the direction of light, but the refractive index difference between regions E1 and E2 also acts to refract light rays entering region E2 more strongly away from normal, causing them to travel a longer optical path through the absorbing material and therefore be more strongly absorbed over a longer path than would be the case without the refractive index difference.

[0152] As can be inferred from the description of Figures 8 to 10, even a small refractive index difference of 0.01 is sufficient to achieve significant angular restriction. Such a small refractive index difference can be achieved, for example, by doping a polymer or transparent silicon as the material for region E1 or E2 of the third optical element 10. In the simplest case, all regions E1 and E2 of the third optical element 10 would be made of the same material. However, additionally, region E1 could be doped with transparent particles to increase the refractive index, and region E2 could be doped with opaque nanoparticles or microparticles to achieve opacity.

[0153] This third optical element 10 can advantageously have a specular reflection on one of its major surfaces, preferably on the first major surface, which is formed as an angle-dependent specular reflection over the entire major surface or as a perfect specular reflection at the surface of region E2.

[0154] The above-described third optical element 10 can be advantageously incorporated into an illumination device for a transmissive image display device such as an LCD panel, which illumination device can then permanently act as a directional backlight and can be used, for example, in embodiments according to the applicant's international patent application WO 2015 / 121398 or international patent application WO 2019 / 002496.

[0155] Figures 27a-c and 28 show various developments of such a third optical element, each connected to a substrate M5, but which is not part of the optical element. As before, the third optical element 10 in this embodiment also has a region E1 made of a first transparent material M1 having a first refractive index N1 and a second region E2 made of a second opaque material M2 having a second refractive index N2. The second opaque material M2 is mixed with an absorbing material so that light is always absorbed in the second region, even if the original material is transparent. The second refractive index N2 is assigned to the transparent region. As shown in Figure 27c in particular, in addition to the first and second regions, a third region made of another opaque material M3 having a third refractive index N3 is formed between each of the two second regions. Here, the third refractive index N3 is greater than the first and second refractive indices N1 and N2. The other opaque material M3 also has a transparent region that determines the third refractive index N3 and a region of absorbing particles that provide opacity. The mass fraction of the absorbing particles in the second opaque material M2 and the further opaque material M3 can be up to 50%, and in individual cases can be higher. When a further opaque material M3 is used, the mass fraction of the absorbing particles in the second opaque material M2 can also be significantly lower than 50%. The particles are symbolized in Figure 28, for example, in the third region M3.

[0156] As shown in Figures 27a and 27b, a second region E2 made of a second opaque material M2 having a second refractive index N2 can be formed between the light-input side of the optical element 10 and a third region made of another opaque material M3, on the one hand, and between the light-output side of the optical element 10 and the light-output surface of the first region E1 made of the first transparent material M1, on the other hand. This is easy to manufacture because the surface made of another opaque material is a continuous, closed layer. As shown in Figure 28, the first region made of the first transparent material M1 and the second region made of the second opaque material M2 can be formed with a trapezoidal cross section. While the trapezoidal shape of the first region E1 can also be used in a variant without another opaque material, it has the advantage of better focusing the angular distribution, thereby further improving the privacy mode / anti-peeping mode when the third optical element 10 is used in a corresponding image display device. 27a, a specular reflective layer M4 is additionally provided at the light entrance surface of the optical element 10 between the substrate and the second region, which is arranged between the substrate and a third region made of a third material M3. In this embodiment, the second region may in particular be a film, i.e. much thinner than the first and third regions, and may in particular extend to the light exit surface of the first region.

[0157] The refractive indices N1, N2, and N3 are configured so that total reflection occurs between a first material M1 having a first refractive index N1 and a second material M2 having a second refractive index N2 at a specific small angle, i.e., the second refractive index N2 is smaller than the first refractive index N1. Preferably, the difference between the first refractive index N1 and the second refractive index N2 is less than 0.1. The third refractive index N3 of another third material M3, which is mixed with an absorbing material like the second material M2, is greater than or equal to, but not smaller than, the first and second refractive indices. As a result, light rays that are not totally reflected at the interface between the first material M1 and the third material M3 are refracted at a larger angle at the interface between the third material and the second material.

[0158] This is illustrated for various cases in Figures 29 and 30. In Case A, the light ray is reflected back off the reflective layer and recycled within the backlight unit (not shown). For light rays with small angles of incidence, in Case B, the light ray is either totally internally reflected at the interface between the first and second regions or passes unimpeded through the first region and the optical element 10. This corresponds to the region in Figure 30 between the origin and the first dashed line on the horizontal axis. The incident angle and the outgoing incident angle are of the same magnitude.

[0159] For light rays entering the first region at angles greater than the angle of total internal reflection at the interface between the first and second regions, two cases must be distinguished depending on the angle of incidence. In case C, shown with a dashed line only to distinguish it from the ray path in case D, the light ray is refracted to a smaller angle at the interface between the first and second regions and leaves the optical element at the exit surface of the second region. This applies only to a fairly small range of angles, depending on the thickness of the second region. In case D, the light ray first enters the second region from the first region at a larger angle of incidence, then enters the third region, where it is refracted to a larger angle upon striking the interface between the second and third regions. Ideally, this results in a significantly smaller range of angles than would be the case without any light or third region, thereby further improving the privacy mode.

[0160] Some of the modifications described above for the first optical element 1 can also be applied to the second optical element 2 and the third optical element 10.

[0161] The optical elements described above solve the problem posed. Optical elements have been described that can affect the direction of diffusion of incident light in a predetermined manner and can optionally be switched between at least two operating states. Each optical element can be implemented inexpensively and is universally compatible with various types of screens, particularly to allow switching between an anti-peeping mode and a free-viewing mode, without substantially reducing or only negligibly reducing the resolution of such screens. Furthermore, these optical elements offer the possibility of realizing a top-hat light distribution.

[0162] The advantages of the present invention are numerous. For example, the above-described operational modes can be achieved with a single optical element that does not require a surface structure. Furthermore, the first and second regions B1 and B2 of the optical element can be embedded in a protective material, such as the material of the first region B1. Furthermore, a highly suitable top-hat distribution of emitted light can be achieved, and theoretical simulations have shown that arbitrarily high privacy contrast can be achieved. When the optical element according to the present invention is used in a backlight for an LCD panel, high brightness can be achieved. Furthermore, a single optical element can simultaneously limit light diffusion in two planes, for example, left and right and top and bottom.

[0163] The above-described invention can be advantageously used in combination with an image display device wherever sensitive data is displayed and / or entered, for example, for PIN entry and data display at ATMs or payment terminals, for password entry, or for viewing email on a mobile device. The invention can also be applied in passenger cars, allowing the driver to selectively block passengers from viewing certain image content, such as entertainment programs. Furthermore, optical elements according to the invention can be used for other technical and commercial purposes, such as light alignment in dark field illumination for microscopes, and light shaping and measurement techniques, most commonly in illumination such as headlights. The above-described embodiment can be described as follows, but is not limited to the following. [Configuration 1] An optical element (1) having a light incident side and a light exit side and extending in a planar shape, the first optical element (1) comprises at least first regions (B1) made of a first transparent material having a first refractive index (N1) and second regions (B2) made of a second transparent material having a second refractive index (N2), the regions being arranged alternately in a one-dimensional or two-dimensional periodic order across the surface of the first optical element (1), wherein the first refractive index (N1) is greater than the second refractive index (N2) over the entire wavelength range visible to the human eye, and further a first layer (OB) at the light entrance surface of each second region (B2) that is permanently opaque or switchable between a transparent state and an opaque state; and a second layer (AB) switchable between a permanently opaque or transparent state and an opaque state, the second layer (AB) being provided on the light output surface of each second region (B2), As a result, light impinging on the optical element (1) on the light entry side, based on the first layer (OB), if the first layer (OB) is in an opaque state, enters the optical element (1) exclusively through the light entry surface of the first region (B1), where, depending on the angle of incidence, the polarization and the ratio of the first refractive index (N1) to the second refractive index (N2), a) propagating unimpeded or undergoing total internal reflection within said first regions (B1) and then being re-emitted at the exit surface of each of said first regions (B1), or b) the light enters the adjacent second region (B2) from the first region (B1), propagates therethrough, and is finally absorbed on the light exit side if the second layer (AB) is opaque, or is emitted if the second layer (AB) is transparent; or c) when light enters the adjacent second region (B2) from the first region (B1), it again enters another adjacent first region (B1) and is either emitted at the light exit surface or propagates further within the optical element (1) depending on the given diffusion direction and polarization, and is finally emitted or absorbed; By doing so, the light exiting the optical element (1) on the light output side has a limited diffusion direction compared to the light impinging on the optical element (1) on the light input side, when at least the first layer (OB) and / or the second layer (AB) are opaque. [Configuration 2] An optical element (1) according to configuration 1, characterized in that each first layer (OB) at the light entrance surface of the second region (B2) is formed by a permanent absorber layer and / or by at least one layer that reflects in a direction away from the optical element (1). [Configuration 3] The optical element (1) according to configuration 1 or 2, characterized in that each second layer (AB) provided on the light-emitting surface of the second region (B2) is formed by a permanent absorber layer. [Configuration 4] 4. The optical element (1) of any one of configurations 1 to 3, characterized in that the first refractive index (N1) of the material in the first region (B1) and / or the second refractive index (N2) of the material in the second region (B2) are switchable between at least two states, so that the ratio (N1, N2) of the two refractive indices at the boundary between the first region (B1) and the second region (B2) is respectively adjustable, thereby varying the restriction in the diffusion direction. [Configuration 5] 5. An optical element (1) according to configuration 4, characterized in that at least one of the materials of the first region (B1) and / or the second region (B2) consists of a liquid crystal in contact with an electrode in order to induce a change in the refractive index for linearly polarized light in the liquid crystal via a change in voltage at the electrode. [Configuration 6] 6. Optical element (1) according to any one of configurations 1 to 5, characterized in that the second layer (AB) and / or the first layer (OB) are switchable between an opaque state and a transparent state, this switchability being preferably based on one or more of the principles of electrowetting, electrophoresis, electrochromism and / or liquid crystal cells. [Configuration 7] 7. The optical element (1) according to any one of configurations 1 to 6, wherein the second layer (AB) and / or the first layer (OB) are embedded in the material constituting the first region (B1), preferably wherein the material portion of the first region (B1) of the optical element (1) seamlessly transitions into the material portion embedding the second layer (AB) and / or the first layer (OB). [Configuration 8] A method for producing the optical element (1) according to any one of configurations 1 to 8, comprising: producing a mold having a positive structure of the first region (B1) and a negative structure of the support; filling a mold with a first polymer that has the first refractive index (N1) after curing; curing the first polymer with ultraviolet light or cooling, after which the workpiece is removed from the mold; filling the structure of the second region (B2) in the workpiece with a second polymer that has the second refractive index (N2) after curing; and curing the second polymer with ultraviolet light or cooling. [Configuration 9] 9. The method of claim 8, wherein after curing the first polymer or the second polymer, an opaque or transparent to opaque switchable material is evaporated or sputtered onto the second region (B2) on the surface of the workpiece through a mask protecting the first region (B1). [Configuration 10] A method for producing the optical element according to any one of aspects 1 to 7, comprising: creating a plurality of base blocks (BL) comprising the second layer (AB) acting as an absorber layer, a second transparent layer made of a material having the second refractive index (N2), the opaque first layer (OB), and a first transparent layer made of a material having the first refractive index (N1) bonded together in this order; a step of stacking the plurality of base blocks (BL) one above the other and joining them to obtain a first stacked block (ST); cutting a disc (SC) having a second layer thickness (D2) from the laminated block (ST); a step of stacking the discs (SC) with the first transparent layer having the first refractive index (N1) and the first thickness (D1) therebetween and bonding them to obtain a second stacked block (SN); and cutting said optical element (1) from said second laminate block (SN). [Configuration 11] 11. The method of claim 10, wherein the first layer (OB) is made reflective. [Configuration 12] 12. Method according to claim 10 or 11, characterized in that the base blocks (BL) are bonded to one another and / or the disc (SC) is bonded to the first transparent layer by vulcanization. [Configuration 13] 13. The method according to any one of configurations 10 to 12, characterized in that the cutting of the disc (SC) from the first laminate block (ST) and / or the cutting of the optical element (1) from the second laminate block (SN) is performed perpendicular to the extension plane of the individual layers. [Configuration 14] A method for limiting the diffusion direction of light that is diffused in a plane in a wavelength range visible to the human eye, comprising: A step of performing planar adjustment of light using a planar opening including at least transparent first regions (C1) and opaque second regions (C2) alternately arranged in a one-dimensional or two-dimensional periodic order on an opening surface; and dividing light propagating through the transparent first region (C1) in the entire wavelength range into a light ray that is reflected within a limit angle of total reflection at the refractive index boundary and finally emitted, and a light ray that transmits through the refractive index boundary outside the limit angle of total reflection and further propagates, and then is absorbed by an absorber, based on the refractive index, in an angle-dependent manner; As a result, the emitted light has a more limited diffusion direction than the light that initially diffuses in a plane. [Configuration 15] An optical element (10) having a light incident side and a light exit side and extending in a planar shape, the optical element (10) comprises at least first regions (E1) made of a transparent material having a first refractive index (N1) and second regions (E2) made of an opaque material having a second refractive index (N2), the regions being arranged alternately in a one-dimensional or two-dimensional periodic order across the surface of the optical element (10), wherein the first refractive index (N1) is greater than the second refractive index (N2) over the entire wavelength range visible to the human eye; As a result, light impinging on the first major surface of the optical element (10) enters the optical element (10) exclusively through the entrance surface of the first region (E1), due to the opaque material of the second region (E2), where, depending on the geometrical direction of incidence, the polarization and the ratio of the first refractive index (N1) to the second refractive index (N2), a) propagating unimpeded or undergoing total internal reflection within said first areas (E1) and then being re-emitted at the exit surface of each said first area (E1), or b) from the first region (E1) into the adjacent second region (E2) where it is absorbed by the opaque material of the second region (E2); Here, since the first refractive index (N1) and the second refractive index (N2) are different, the light entering the second region (E2) is more strongly refracted in a direction away from the perpendicular line, This method allows light exiting the optical element (10) at its second major surface to have a more restricted diffusion direction than light impinging on the optical element (10) at its first major surface. [Configuration 16] 16. An optical element (10) according to claim 15, characterized in that the opaque material consists of a transparent material having the second refractive index (N2), which is mixed with absorbing particles, thereby producing an overall opaque effect. [Configuration 17] 17. The optical element (10) of claim 15 or 16, wherein the opaque material consists of graphite particles having a size of less than 500 nm, black carbon nanoparticles having a size of less than 200 nm, a lacquer or a polymer mixed with a dye or a dye mixture as absorbing particles. [Configuration 18] 18. The optical element according to claim 16 or 17, wherein the mass fraction of the absorbing particles is at most 50%. [Configuration 19] 19. An optical element (10) according to any one of configurations 15 to 18, characterized in that one of the two major surfaces, preferably the first major surface, has a specular reflection formed as an angle-dependent specular reflection over the entire major surface or as a perfect specular reflection at the surface of the second region (E2). [Configuration 20] An optical element (10) according to any one of configurations 15 to 19, characterized in that between each two of the second regions (E2), a third region made of another opaque material (M3) having a third refractive index (N3) is formed, and the third refractive index (N3) is greater than the first refractive index (N1) and greater than the second refractive index (N2). [Configuration 21] The optical element (10) described in structure 20, characterized in that the second region (E2) is also formed between the light incident side of the optical element (10) and the third region, and between the light exit side of the optical element (10) and the light exit surface of the first region (E1). [Configuration 22] 22. The optical element (10) according to configuration 20 or 21, characterized in that the magnitude of the difference in refractive index between the first refractive index (N1) and the second refractive index (N2) is less than 0.1. [Configuration 23] The optical element (1, 10) according to any one of configurations 1 to 7 or 15 to 22, characterized in that the first regions (B1, E1) and the second regions (B2, E2) are arranged so as to be distributed in alternating bands across the entire surface of the optical element (1, 10) when viewed in a parallel projection perpendicular to the optical element (1, 10). [Configuration 24] The optical element (1, 10) according to any one of configurations 1 to 7 or 15 to 22, characterized in that the first regions (B1, E1) are arranged so as to be distributed in a dot-like, circular, elliptical, rectangular or hexagonal shape over the entire surface of the optical element (1, 10) when viewed in a parallel projection perpendicular to the optical element (1, 10), and the second regions (B2, E2) are shaped complementarily thereto. [Configuration 25] The optical element (1, 10) described in any one of configurations 1 to 7 or 15 to 24, characterized in that the first region (B1, E1) and the second region (B2, E2) are formed in a trapezoidal shape when viewed in a cross-sectional direction perpendicular to the top surface of the optical element (1, 10). [Configuration 26] An optical element (1, 10) according to any one of configurations 1 to 7 or 15 to 25, characterized in that in at least a part of the first regions (B1, E1), preferably in all of the first regions (B1, E1), a lens structure (L), preferably a convex lens structure, is applied to their light exit side. [Configuration 27] 27. The optical element (1, 10) according to any one of configurations 1 to 7 or 15 to 26, characterized in that a polarizer, preferably a reflective polarizer, is arranged on the light input side and / or the light output side of the optical element (1, 10). [Configuration 28] 28. An optical element (1, 10) according to any one of configurations 1 to 7 or 15 to 27, characterized in that at least one first region (B1, E1) is formed on the optical element (1, 10), the shortest extension of which, as viewed in a parallel projection perpendicular to the optical element (1, 10), is at least 20 times greater than the shortest extension of all of the second regions (B2, E2) as viewed in a parallel projection perpendicular to the optical element (1, 10), and in that, within the at least one first region (B1, E1), except for its edges and parallel displacements, the diffusion direction of light leaving the optical element (1) on the light output side is not limited compared to light impinging on the light input side of the optical element (1). [Configuration 29] An optical element (1, 10) described in any one of configurations 1 to 7 or 15 to 28, characterized in that in addition to the first region (B1, E1) and the second region (B2, E2), other regions are formed having parameters different from those of the first region (B1, E1) and the second region (B2, E2) in terms of shape and / or refractive index, and light that passes through these other regions and exits the optical element (1, 10) is restricted in a diffusion direction different from that of the first region (B1, E1). [Configuration 30] A method for producing an optical element (10) according to any one of aspects 15 to 18, comprising the steps of: A step of alternately stacking first layers made of a transparent material having the first refractive index (N1) and second layers made of an opaque material having the second refractive index (N2), wherein the first refractive index (N1) is greater than the second refractive index (N2); bonding the first layer and the second layer together; and cutting the optical element (10) from the layer composite. [Configuration 31] 30. Use of the optical element (1, 10) according to any one of configurations 1 to 7 or 15 to 29 with an image display device (3), or a backlight (BLU) for a transmissive image display device (LCD), for the purpose of selectively restricting the viewing direction of the image display device (3, LCD).

Claims

1. An optical element (10) having a light entrance side and a light exit side and extending in a planar shape, the optical element (10) comprises at least first regions (E1) made of a transparent material having a first refractive index (N1) and second regions (E2) made of a permanently opaque material having a second refractive index (N2), the regions being arranged alternately in a one-dimensional or two-dimensional periodic sequence across the surface of the optical element (10), wherein the first refractive index (N1) is greater than the second refractive index (N2) over the entire wavelength range visible to the human eye; The first region (B1, E1) and the second region (B2, E2) are formed in a trapezoidal shape when viewed in a cross section perpendicular to the top surface of the optical element (1, 10), and at least the first region (E1) has a cross section of an isosceles trapezoid, and the long base of the trapezoid corresponds to the light output surface of the corresponding first region (E1); As a result, light impinging on the first major surface of the optical element (10) enters the optical element (10) exclusively through the light entrance surface of the first region (E1), due to the opaque material of the second region (E2), where, depending on the geometrical direction of incidence, the polarization and the ratio of the first refractive index (N1) to the second refractive index (N2), a) propagating unimpeded or undergoing total internal reflection within said first areas (E1) and then being emitted again at the exit surface of the respective first area (E1), or b) from said first region (E1) into the adjacent second region (E2) where it is absorbed by the opaque material of said second region (E2); Here, since the first refractive index (N1) and the second refractive index (N2) are different, the light entering the second region (E2) is more strongly refracted in a direction away from the normal, so that light exiting the second major surface of the optical element (10) has a limited diffusion direction compared to light impinging on the optical element (10) at the first major surface; An optical element (10) having a specular reflection on one of its two main surfaces, formed either as an angle-dependent specular reflection over the entire main surface or as a perfect specular reflection at the surface of said second region (E2).

2. 2. The optical element (10) according to claim 1, characterized in that the opaque material consists of a transparent material having the second refractive index (N2), which is mixed with absorbing particles, thereby producing an overall opaque effect.

3. 3. An optical element (10) according to claim 1 or 2, characterized in that the opaque material consists of a lacquer or a polymer mixed with graphite particles having a size of less than 500 nm, black carbon nanoparticles having a size of less than 200 nm, a dye or a dye mixture as absorbing particles.

4. 4. An optical element (10) according to claim 1, characterized in that between each two of the second regions (E2), a third region made of another opaque material (M3) having a third refractive index (N3) is formed, the third refractive index (N3) being greater than the first refractive index (N1) and greater than the second refractive index (N2).

5. The optical element (10) of claim 4, characterized in that the second region (E2) is also formed between the light-entering side of the optical element (10) and the third region, and between the light-exiting side of the optical element (10) and the light-exiting surface of the first region (E1).

6. 6. An optical element (1, 10) according to claim 1, characterized in that the first regions (B1, E1) and the second regions (B2, E2) are arranged in alternating stripes distributed over the entire surface of the optical element (1, 10) when viewed in a parallel projection perpendicular to the optical element (1, 10).

7. 7. The optical element (1, 10) according to claim 1, wherein the first regions (B1, E1) are arranged so as to be distributed in a dot-like, circular, elliptical, rectangular or hexagonal shape over the entire surface of the optical element (1, 10) when viewed in a parallel projection perpendicular to the optical element (1, 10), and the second regions (B2, E2) are shaped complementarily thereto.

8. 8. An optical element (1, 10) according to any one of claims 1 to 7, characterized in that in addition to the first region (B1, E1) and the second region (B2, E2), other regions are formed having parameters different from those of the first region (B1, E1) and the second region (B2, E2) in terms of shape and / or refractive index, and light passing through these other regions and exiting the optical element (1, 10) is restricted in a diffusion direction different from that of the first region (B1, E1).

9. 9. Use of the optical element (1, 10) according to any one of claims 1 to 8 with an image display device (3) or a backlight (BLU) for a transmissive image display device (LCD) for the purpose of selectively restricting the viewing direction of the image display device (3, LCD).

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