Optical Components

Abstract

The present invention relates to an optical element (1), comprising: a substrate (S) having a first and a second large surface; a plurality of opaque surfaces (O1, O2, ...) located near or on the first large surface; in a first alternative, a plurality of surfaces (S1, S2, ...) located near or on the second large surface and capable of switching between opaque and transparent states, or in a second alternative, a plurality of chambers (K1, K2, ...) located in the substrate (S), the chambers being filled with a liquid (F), wherein the liquid (F) contains up to 30% by volume of particles (P) capable of electrophoretic mobility and capable of absorbing light, the particles being capable of being positioned in the corresponding chambers (K1, K2, ...) by means of an electromagnetic field that can be varied in at least two different states.

Description

Technical Field

[0001] In recent years, great progress has been made in widening the viewing angle in LCDs. However, there are often situations where very large viewing areas of a display can be a drawback. Information, such as banking data or other personal and sensitive data, is increasingly available via mobile devices such as laptops and tablets. People therefore need to control who can see this sensitive data; these people need to be able to choose between wide viewing angles for sharing information with others on a display, such as when viewing vacation photos or for advertising purposes. On the other hand, smaller viewing angles are required when they want to work with image information privately.

[0002] Similar problems arise in vehicle construction: There, the driver cannot be distracted by graphic content (e.g. digital entertainment) while the engine is running, while the passengers also want to consume the same content while driving. A display screen is therefore required that can be switched between the corresponding display modes. Background Art

[0003] Additional films based on micro-lamellae are already used for mobile displays for optical data protection. However, these films cannot be switched; they always have to be applied manually and then removed again. They also have to be transported separately from the display when they are not needed. A significant disadvantage of using such thin films is also related to the associated light losses.

[0004] Document US5,956,107A discloses a switchable light source, with which a display screen can be operated in multiple modes. The disadvantage here is that all light coupling-out is based on scattering, so only low efficiency and non-optimal light direction effects can be achieved. In particular, the implementation of the focused light cone is not disclosed in more detail.

[0005] CN107734118A introduces a display screen that can control the viewing angle of the display screen by means of two backlighting devices. To this end, the upper backlighting device of the two backlighting devices should emit focused light. As a construction for this, a grid with opaque and transparent segments is used. However, this may cause the light of the second backlighting device (which must penetrate the first backlighting device in the direction of the LCD panel) to also be focused, so that the common viewing mode used to provide a wide viewing angle in practice will significantly reduce the angle.

[0006] US 2007 / 030240 A1 describes an optical element for controlling the light propagation direction of light originating from a backlighting device. Such an optical element requires liquid crystals in the form of PDLC, for example, which are expensive on the one hand but are safety-critical on the other hand, especially for end-customer applications, since PDLC liquid crystals generally require voltages higher than 60V for their circuits.

[0007] In CN1987606A, a display screen is again described, which uses two backlighting devices to control the viewing angle of the display screen. In particular, a "first light plate" is used here, which must be wedge-shaped in order to achieve the desired focused light outcoupling. The exact details of achieving focused light outcoupling under appropriate angle conditions are not disclosed.

[0008] In addition, US2018 / 0267344A1 introduces a structure with two planar lighting modules. Here, the light of the lighting module placed behind in the viewing direction is focused by a separate structure. After focusing, the light beam still needs to pass through the lighting module in front, which has a scattering element. Therefore, strong light focusing cannot achieve optimal viewing protection.

[0009] Finally, US2007 / 0008456A1 discloses dividing the light emission angle into at least three regions, wherein light is usually applied to two of the regions. Thus, when using such a light-emitting display, viewing protection that cannot be viewed from only one direction is achieved.

[0010] WO 2015 / 121398 A1 of the applicant describes a display screen of the type mentioned at the outset. In it, mainly scattering particles are present in the volume of the corresponding light guide for switching the operating mode. However, the scattering particles made of polymers selected in this document generally have the following disadvantages: light is coupled out from two large surfaces, whereby about half of the useful light is directed in the wrong direction, i.e. towards the backlighting device, where it cannot be fully recovered for structural reasons. In addition, the polymer scattering particles distributed in the light guide volume may, especially in higher concentrations, lead to scattering effects, thereby reducing the viewing protection effect in the protected operating mode.

[0011] US2020 / 012129A1 discloses an illumination device and a display screen, which introduces two lamps for switching between a narrow viewing mode and a wide viewing mode. On the one hand, one of the light guides is constructed with fibers. On the other hand, the scattering coupling-out structure of the light guide is limited to a certain strip in the projection direction. This is disadvantageous for uniform image illumination and often also causes undesirable moiré effects in the structure, for example in conjunction with pixel columns or rows of an LCD panel located above.

[0012] The above methods and devices generally have the following disadvantages: they significantly reduce the brightness of the basic display and / or require active or at least special optical elements for mode switching and / or require complex and expensive production requirements and / or reduce the resolution in free-view mode. Summary of the invention

[0013] The object of the invention is therefore to provide an optical element which can influence the transmittance as a function of the angle and which can be switched between at least two states. The optical element should be cost-effective to produce and, in particular, universally usable for different types of display screens in order to be able to switch between a protected viewing mode and a free viewing mode. In addition, a display screen and a display screen lighting device based on the optical element are described.

[0014] According to the present invention, this object is achieved by an optical element, which comprises: (i) a substantially plate-shaped or shell-shaped substrate S having a first and a second large surface, wherein one of the large surfaces serves as a light entrance surface and the other large surface serves as a light exit surface for light incident on the optical element, (ii) a plurality of opaque surfaces O1, O2, ... located near or on the first large surface, (iii) in a first alternative, a plurality of surfaces S1, S2, ... located near or on the second large surface that can be switched between an opaque and a transparent state, or in a second alternative, a plurality of chambers K1, K2, ... in the substrate S, which are filled with a liquid F, wherein the liquid F contains electrophoretically or magnetophoretically movable particles P in a maximum of 30% by volume, preferably a maximum of 20% by volume, which particles can absorb light of one or more wavelengths or wavelength ranges and can be positioned in the corresponding chamber K1 by a variable electromagnetic field in at least two different states. , K2, ..., (iv) thereby: in the first state, in the first alternative, the switchable surfaces S1, S2, ... are in an opaque state, and in the second alternative, more than half of all the particles P, particularly preferably more than 90% of all the particles P are located in the half, preferably one third, of the corresponding chambers K1, K2, ... facing away from the first large surface, the optical element limits the light incident on the light incident surface in its propagation direction, (v) and: in the second state, in the first alternative, the switchable surfaces S1, S2, ... are in a transparent state, and in the second alternative, more than half of all the particles P, particularly preferably more than 90% of all the particles P are located in the half of the corresponding chambers K1, K2 facing the first large surface, the optical element does not limit the light incident on the light incident surface in its propagation direction, but only a part of the light cannot be transmitted due to the opaque surfaces O1, O2, ...

[0015] Here, “near” relative to the opaque surfaces O1, O2, ... and the switchable surfaces S1, S2, ... means that the distance of these surfaces to the corresponding large surface is not greater than the thickness of the substrate S. Here, it is conceivable that the opaque surfaces O1, O2, ... and / or the switchable surfaces S1, S2, ... are arranged inside or outside the substrate S.

[0016] It preferably applies that in the second state the angle-dependent transmission is greater than 30%, preferably greater than 50%, and in the first state the angle-dependent transmission is less than 5%, preferably less than 3%, particularly preferably less than 2%, within an angle range of greater than 30° (this angle can also vary, for example 10°, 20°, 25°, 40° or 45°) relative to the second surface normal of the large surface of the substrate S and measured in an optional direction perpendicular to the longitudinal extension of the substrate S, preferably measured in the horizontal direction. In the first state, the propagation direction of the light penetrating the optical element is significantly restricted, except for a small residual portion.

[0017] The first large surface of the substrate S may be the large surface at the front or at the rear when viewed from the observation direction, depending on the application.

[0018] The (permanent) opaque surfaces O1, O2, ... are preferably designed in strip form. However, it is also possible that the opaque surfaces O1, O2, ... are distributed separately from each other on the entire first large surface or in the vicinity of the first large surface in a two-dimensional pattern that can be periodic or aperiodic. This exemplary possible two-dimensional pattern can be composed of two opaque grids that cross, for example, at 90 degrees, i.e., rectangular or square, non-opaque partial surfaces are surrounded by opaque surfaces O1, O2, ... from all four sides.

[0019] Accordingly, in the first alternative, when the opaque surfaces O1, O2, ... are designed as strips, the switchable surfaces S1, S2, ... are also strips. In addition, the switchable surfaces S1, S2, ... have shapes similar or identical to those of the opaque surfaces O1, O2, ...

[0020] Furthermore, in a first alternative, in the first state of the optical element, a maximum transmission is generally present in one or more directions parallel to the (imaginary) line between the surface centers of the respective intermediate surfaces of each of two switchable surfaces S1, S2 ... and the respective surface centers of the intermediate surfaces between the immediately adjacent (permanently) opaque surfaces O1, O2 ..., wherein the switchable surfaces S1, S2 are preferably located in front of the opaque surfaces O1, O2, ... as viewed from the direction of the observer. Each two opaque surfaces O1, O2, ... and each two switchable surfaces S1, S2, ... are separated by a transparent intermediate surface. The closest to a switchable surface is the opaque surface which is at the shortest distance to the switchable surface in question; the same applies to the intermediate surfaces.

[0021] In the simplest case, the switchable surfaces S1, S2, ... and the opaque surfaces O1, O2, ... correspond to each other in terms of size and position, so that: in the projection along the direction perpendicular to the large surface, the switchable surfaces and the opaque surfaces are congruent. In this case, the maximum value of the transmittance is in the direction perpendicular to the large surface, because the connecting line of the intermediate surfaces also extends perpendicular to the large surface; in the case of a shell-shaped substrate, the maximum transmission direction can be focused on the observer in this way.

[0022] However, the switchable surfaces S1, S2, ... and the opaque surfaces O1, O2, ... can also be arranged offset from each other in relation to the projection along a direction perpendicular to the large surface, and if necessary, also offset by different magnitudes, so that the connecting line of the surface centers of the intermediate surfaces encloses an angle not equal to 90° with the large surface or, if necessary (such as in the case of a shell-shaped substrate), an angle not equal to 0° with its position-dependent normal. This is particularly meaningful for a plate-shaped substrate: if all connecting lines of the intermediate surfaces enclose the same angle not equal to 90° with the large surface, the transmission maximum for the virtual observer will be moved to the position he sees along the connecting line, i.e., an inclined angle not equal to 90°. In particular, in the case of a plate-shaped substrate, the following design is advantageous, wherein the switchable surfaces S1, S2, ... and the opaque surfaces O1, O2, ... are arranged in such a way that all connecting lines enclose different angles, i.e., different angles in pairs, with the large surface, wherein the connecting lines particularly preferably intersect at one point. A virtual observer at the intersection perceives the maximum transmittance only at the intersection and in a very narrow area around the intersection; when the viewing position moves away from the intersection, the transmittance drops sharply, for example, the intensity distribution corresponds to a top-hat distribution.

[0023] The above-described embodiments regarding the ratio of the opaque surfaces O1, O2, ... to the switchable surfaces S1, S2, ... can also be applied analogously to the ratio of the chambers K1, K2, ... to the switchable surfaces S1, S2, .... Here, too, the switchable surfaces S1, S2, ... are located in front of the chambers K1, K2, ... and connecting lines can be constructed for the corresponding transparent intermediate surfaces.

[0024] Furthermore, it is possible that, in a first alternative, the switchable surfaces S1, S2, ... comprise at least one electrochromic layer, an LC cell, an electrowetting cell and / or an LC film with a dichroic dye (e.g. in the form of a "black PDLC" film). Other variants are conceivable and fall within the scope of the invention.

[0025] Alternatively, it is possible that in a first alternative, the switchable surfaces S1, S2, ... can include fluid chambers R, each containing a liquid F, which contains electrophoretically or magnetophoretically movable particles P in a volume percentage of up to 30%, preferably up to 20%, which absorb light of one or more wavelengths or wavelength ranges, wherein an electromagnetic switching mechanism is formed in a planar manner on one or more sides of the fluid chamber R, which generates an electromagnetic field effective in the fluid chamber R in the switched-on state, whereby the particles P move in the liquid so that the position and / or orientation of the particles can be switched between at least two of the states, which generate the opaque and transparent states of the switchable surfaces S1, S2, ... In the first state, the particles P are preferably distributed over the entire surface of the switchable surfaces S1, S2, ..., while in the second state, the particles are gathered in the smallest possible volume in order not to cover the largest possible surface area of ​​the switchable surfaces S1, S2, ...

[0026] The wavelength or wavelengths or wavelength ranges at which the electrophoretically or magnetophoretically movable particles absorb light are preferably in the visible spectrum and particularly preferably cover the visible spectrum substantially completely. However, for special purposes, the wavelengths or wavelength ranges mentioned above can also be outside the visible spectrum, for example when ultraviolet or infrared light is to be affected (e.g. for measurement technology purposes).

[0027] The electromagnetic switching mechanism formed in a flat manner on one or more sides of the fluid chamber R in the substrate S is arranged on a narrow side or a large surface of the corresponding fluid chamber R, for example.

[0028] The particles P are, for example, nanoparticles, quantum dots and / or dyes. The particles have a spatial extension of at most 200 nm, preferably at most 100 nm, particularly preferably at most 50 nm. The spatial extension is the maximum extension in three-dimensional space or the hydrodynamic radius, whichever is greater. For spherical particles, the spatial extension is the diameter. For rope-shaped particles P, the spatial extension is the maximum possible distance that two points on the particle surface can have from each other.

[0029] In another advantageous embodiment, a plurality of types of particles P are present in the liquid, which differ in their absorption and / or transmission properties in the electromagnetic field. The "transmission properties" refer in particular to the properties of the particles P during the corresponding electrophoresis (transmission in the field).

[0030] Such variations are particularly critical in the case of nanoparticles if the particle types differ, for example, in terms of particle size and / or surface functionality, ie, zeta potential.

[0031] When quantum dots or dyes are used as particles P and when these particles are fluorescent, preference is given to using so-called “quencher” materials in order to simultaneously avoid fluorescence.

[0032] The liquid F can be polar or non-polar. These liquids can also be composed of, for example, water, oil, toluene or formaldehyde, also mixed with 10% by volume of ferrofluid and / or electrolyte.

[0033] Furthermore, the particles P are charged and the electromagnetic switch mechanism is designed as an electrode for generating a static or dynamic electric field, or the particles P are magnetic and the electromagnetic switch mechanism is designed as an electromagnetic layer for generating a static electric field or a dynamic magnetic field, so that the electromagnetic particles P move in the electric field or magnetic field in the liquid F. Then, the corresponding electric field lines are designed, for example, in parallel in the center of the fluid chamber R, and only show deviations from parallelism at the edges. However, other designs are also feasible. When an electromagnetic field, in particular a static field, is applied, the main physical effect of the movement of the particles P is (double) electrophoresis or magnetophoresis.

[0034] For example, the width of the fluid chambers R in a plane parallel to the main propagation direction of the substrate S can be between 2 μm and 50 μm (distance from long side to long side of the fluid chambers), and can be spaced at a minimum of 10 μm to about 150 μm from one another (distance from long side to long side of adjacent fluid chambers R). The depth of the fluid chambers R can be from a few micrometers to about 50 μm. However, values ​​different from those presented here are obviously also feasible.

[0035] Furthermore, the switchable surfaces S1 , S2 , . . . can be divided into at least two groups which can each be switched independently of one another, so that local switchability between the first state and the second state is achieved on the optical element.

[0036] In a first alternative design of the optical element, the optical element may also include a mechanism for suppressing a light beam propagating in the substrate S, which is either emitted into the substrate S from a gap between two adjacent opaque surfaces O1, O2 or from a gap between two adjacent switchable surfaces S1, S2 in the opaque state of the switchable surfaces S1, S2, ... and is directed to the respective switchable surfaces S3, S4 on the respective opposite large surfaces of the substrate S or to the respective non-immediate gaps between the opaque surfaces O3, O4. The mechanism may be designed, for example, in such a way that, based on a suitable choice of the refractive index of the substrate S compared to the refractive index of the medium surrounding the substrate S, a certain light beam at a determinable angle cannot leave the substrate S due to total reflection.

[0037] Alternatively, the mechanism can be formed in the following manner, respectively, so that absorbers are embedded between some or all of the opaque surfaces O1, O2, ... in the substrate S, and the absorbers basically extend from the first large surface of the substrate to the second large surface S and are approximately perpendicular to one of the large surfaces. In addition, the mechanism can be implemented by appropriately selecting the thickness of the opaque surfaces O1, O2, ... and / or the switchable surfaces S1, S2, .... A plurality of the above-mentioned measures for implementing the mechanism can also be combined with each other.

[0038] In order to better distinguish the first and second alternatives, in the second alternative the chambers K1 , K2 , . . . which are present here and filled with the liquid F are referred to as “chambers”, although in reality they are also equivalent to fluid chambers.

[0039] In the second alternative of the optical element, it is preferably applicable that: each chamber K1, K2, ... is located above the opaque surfaces O1, O2, ... along the projection direction perpendicular to the substrate S. In addition, it is advantageous that: in the second alternative, an electromagnetic switching mechanism is constructed in a planar manner on one or more sides of the chambers K1, K2, ..., and when the electromagnetic switching mechanism is turned on, an effective electromagnetic field is generated in the chambers K1, K2, ..., whereby the particles P move in the liquid so that the position and / or orientation of the particles P can be switched between at least two states, and the states generate at least two states of the optical element. The electromagnetic switching mechanism is preferably an electrode, wherein at least the electrode on the second large surface is (at least partially) transparent. The electrode on the first large surface is arranged on or near the opaque surfaces O1, O2, ..., or when the electrode is an opaque electrode, it can even be equivalent to these surfaces.

[0040] With regard to the dimensions of the chambers K1 , K2 . . . in the second alternative, reference is made to the design variants of the fluid chambers given above for the first alternative of the optical element. In particular, however, the depth of such chambers K1 , K2 . . . can also be greater than 50 μm, for example 100 μm.

[0041] The general design description of the liquid F and the particles P as given above for the first alternative also applies to the second alternative and is therefore not repeated here. The significant difference between the configurations according to the first alternative and the second alternative is that in the first alternative, the particles P cause the corresponding switchable surfaces S1, S2, ... to be switched to be as opaque as possible in one state and to be as transparent as possible in another state, i.e. the particles P move horizontally, whereas in the second alternative, the particles P move vertically between the two states in order to achieve or avoid the desired influence on the light propagation direction by cooperating with the opaque surfaces O1, O2, ...

[0042] For the optical element in the second alternative, in the first state, at least four fifths, particularly preferably more than nine tenths, of all particles P are located in the third, preferably the quarter, of the corresponding chambers K1 , K2 , . . . that are adjacent to the second largest surface of the substrate S.

[0043] Furthermore, the chambers K1, K2, . . . can be divided into at least two groups, which can be switched independently of each other, so that local switchability between the first state and the second state on the optical element is achieved.

[0044] A particularly advantageous design of the optical element in the second alternative is that the space between the respective adjacent chambers K1, K2, ... in the substrate S has a higher refractive index than the liquid F in the chambers K1, K2, ..., wherein this applies at least to at least one wavelength in the visible light range, but preferably to all wavelengths in the range of 400 nm to 800 nm (inclusive). The refractive index difference can be, for example, 0.01 or 0.02 or 0.03 or more.

[0045] This achieves the following: for example, light irradiated onto the optical element on the first large surface enters the optical element only through a portion of the surface of the first large surface between the opaque layers O1, O2, ... based on the opaque layers O1, O2, ... and there, depending on the incident direction, polarization and the above-mentioned refractive index difference, a) is totally reflected between the two chambers K1, K2, ... and then coupled out again on the upper surface of the corresponding area of ​​the substrate S (here, on the second large surface) (case a), or b) overcomes the refractive index boundary from the substrate material to the liquid F and enters a chamber adjacent to the liquid F, propagates in the chamber and finally forms a substrate on its upper side. The particles P are absorbed in the first state, or coupled out when the second state exists (case b), or c) after overcoming the refractive index boundary from the substrate material to the liquid F, they overcome the next refractive index boundary from the liquid F to the next adjacent substrate material, and are coupled out or continue to propagate in the first optical element according to the propagation direction and polarization given at that time, until they are either coupled out or absorbed according to the state in the optical element (case c), or d) in both states, the substrate S passes between the two chambers K1, K2 without total reflection and is coupled out again from the optical element on the second large surface (case d). This description applies similarly to the case where light is irradiated onto the optical element via the second large surface; the light path is of course reversible.

[0046] The differences in refractive index described and defined above according to their effects can also be used in principle for the first alternative of the optical element: in this case, those areas in the substrate that are respectively located between the opaque surfaces O1, O2 ... and the switchable areas S1, S2 ... that are adjacent thereto have a lower refractive index than the areas complementary to these areas. Instead of the chambers K1, K2, ..., those volume areas of the substrate S have a lower refractive index than the surrounding volume areas of the substrate S, which are respectively located between the opaque surfaces O1, ... and the areas S1, ... between the adjacent switchable areas, wherein "adjacent" here means along the surface normal of the first large surface that is only locally defined in the case of a shell-shaped substrate in the direction of the second large surface. In principle, therefore, situations a) to d) can also be generated there or selected from them. Here, this also applies to at least one wavelength in the visible light range, but preferably to all wavelengths in the range of 400nm to 800nm.

[0047] The advantage of this embodiment is that the light which is confined by the optical element in its direction of propagation in the first state has an approximately top-hat distribution, i.e. the brightness has only a small angular dependence around the preferred direction of propagation, which is then followed by a sharp drop in transmittance. The described transmittance dependence has the advantage that an observer from the preferred direction perceives the transmittance uniformly and for an observer from an angle of, for example, greater than 30° (this angle can also vary, for example 10°, 20°, 25°, 40° or 45°), the transmittance is greatly reduced.

[0048] In a second alternative embodiment of the optical element according to the invention, the refractive index of the substrate material (at least between two adjacent chambers K1, K2, ...) and / or the refractive index of the liquid F in the chambers K1, K2, ... can be switched between at least two states, so that the refractive index difference at the corresponding refractive index boundaries can be modulated, whereby the said restriction or influence on the propagation direction can be changed.

[0049] An advantageous design is also produced in the following way: each opaque surface O1, O2, ... is formed by a permanent absorption layer and / or at least one downward reflecting layer. If only one reflecting layer is present here (which is possible within the scope of the invention), then this reflecting layer will of course also have opaque properties. For example, when the optical element according to the invention is installed in a lighting device (for example for an LCD panel), the reflective properties help to increase the efficiency.

[0050] The optical element can advantageously be combined with a polarizer which polarizes the transmitted light linearly parallel to the preferred viewing protection direction.

[0051] In two alternatives of the optical element, the substrate S may form a cover substrate of an OLED, microLED or LCD panel, the cover substrate having pixels or sub-pixels, respectively. Alternatively, the substrate S may be applied to said cover substrate or positioned in front of it.

[0052] What is advantageous for the first alternative here is that the surface center of each area between the switchable surfaces S1, S2, ... and / or the opaque surfaces O1, O2, ... is located in front of the center point of the pixel or sub-pixel of the corresponding panel in a vertical projection onto the substrate S with a tolerance of up to 20% of the width of each such area.

[0053] However, alternatively, it is also feasible that the surface center of each area between the switchable surfaces S1, S2, ... and / or the opaque surfaces O1, O2, ... can be slightly offset in front of the center point of one of the pixels or sub-pixels of the corresponding panel in the vertical projection onto the substrate S, so that the imaginary connecting line of the corresponding surface centers of the switchable surfaces S1, S2, ... is connected to the imaginary connecting line of the opaque surfaces O1, O2, ... with a tolerance of a maximum of 15° toward the viewer. Therefore, the light transmitted in the first state of the optical element will be focused toward the observer.

[0054] A variation of the area size of the switchable regions S1 , S2 , . . . and / or the opaque surfaces O1 , O2 , . . . is also possible in order to further adjust the transmission properties of the optical element.

[0055] In this way, in the second alternative, for example, the upper face of the chamber may be smaller than the lower face of the chamber, which generally corresponds to the opaque faces O1 , O2 , ... This enables the transmittance to be focused towards the viewer.

[0056] Furthermore, in two alternatives of the optical element, it is possible that the opaque surfaces 01, O2, . . . can be arranged on or near a large surface behind the substrate S in the viewing direction of the observer and perform specular reflection or partial specular reflection on the side facing away from the observer.

[0057] According to the present invention, another part of the purpose of the present invention is achieved by a lighting device for a display screen, which can be operated in a first state for a restricted viewing mode and in a second state for a free viewing mode, comprising: a backlighting device extending in a planar manner, which emits light into an unrestricted angle range, and an optical element located in front of the backlighting device in the viewing direction, as described above.

[0058] The backlighting device used here preferably emits light into an unlimited angle range. However, the backlighting device can also have a certain pre-focus, for example in the form of: it shines into an angle range (measured horizontally) exceeding 30 ° or 45 ° at no more than 10% or 20% of the peak brightness along the horizontal.

[0059] Such an illumination device is advantageously used together with a transmissive image display unit arranged in front of the optical element in the viewing direction in order to obtain a display screen capable of operating in a first state corresponding to a restricted viewing mode and in a second state corresponding to a free viewing mode, since the light from the illumination device is sometimes restricted in the propagation direction due to the optical element, i.e. focused (first state), and sometimes unfocused (second state).

[0060] According to the present invention, the last part of the purpose of the present invention is achieved by a display screen, which can operate in a first state corresponding to a restricted viewing mode and in a second state corresponding to a free viewing mode. The display screen includes an optical element as described above, and an image display unit in front of or behind the optical element from the viewer's perspective.

[0061] The image display unit is, for example, an OLED display, an LCD, a SED, a FED, a microLED display or a VFD. Since the optical element is effective regardless of the type of the image display unit, any other type of display screen may also be used.

[0062] The lighting device with a display screen according to the invention and the display screen according to the invention are particularly advantageously used in a vehicle for selectively displaying image content only for a front passenger in a first state or for displaying image content simultaneously for the driver and the front passenger in a second state. The first state is useful, for example, when a passenger is watching entertainment content that could distract the driver.

[0063] The invention is also used to enter or display confidential data (such as a PIN number, email, SMS or password) at an ATM, payment terminal or mobile device.

[0064] Furthermore, the desired restricted propagation directions for the first state of restricted view may be defined and implemented independently of each other for the horizontal and vertical directions. For example, a larger angle in the vertical direction than in the horizontal direction (or possibly no restriction at all) may be more reasonable, e.g. if people of different heights should be able to see the image at an ATM, while sideways viewing should remain largely or completely restricted. However, for POS payment terminals, it is usually necessary to restrict visibility in the first state in both horizontal and vertical directions due to security regulations.

[0065] In principle, if the above parameters are varied within certain limits, the performance of the present invention can still be achieved.

[0066] Of course, the features mentioned above and those yet to be explained below can be used not only in the combination specified but also in other combinations or alone, without departing from the scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] The present invention will be explained in more detail based on embodiments with reference to the accompanying drawings, which also reveal the essential features of the present invention. These embodiments are for illustrative purposes only and should not be construed as limiting. For example, the introduction of embodiments including multiple elements or components should not be construed as meaning that all these elements or components are necessary for implementation. On the contrary, other embodiments may also include alternative elements and components, fewer elements or components, or additional elements or components. Unless otherwise indicated, the elements or components of different embodiments may be combined with each other. The modifications and variations introduced for one of the embodiments may also be applicable to other embodiments. In order to avoid repetition, the same or corresponding elements in different drawings are represented by the same reference numerals and are not explained multiple times. Wherein:

[0068] Figure 1a a schematic diagram showing a first design of an optical element in a first alternative;

[0069] Figure 1b a schematic diagram showing a second design of the optical element in the first alternative;

[0070] Figure 2 a schematic diagram showing a third design of the optical element in the first alternative;

[0071] Figure 3 a schematic diagram showing a first design of an optical element in a second alternative;

[0072] Figure 4 a schematic diagram showing a second design of an optical element in a second alternative;

[0073] Figure 5 Schematic diagram showing a variation of the positioning of the switchable surface compared to the opaque surface in the first alternative of the optical element;

[0074] Figure 6 A schematic diagram showing a first variant of the surface size of the switchable surface compared to the opaque surface in the first alternative of the optical element;

[0075] Figure 7 A schematic diagram showing a second variant of the surface size of the switchable surface compared to the opaque surface in the first alternative of the optical element;

[0076] Figure 8 Schematic diagram showing a variation of the surface dimensions of the upper face of the chamber compared to the opaque face in the second alternative of the optical element;

[0077] Fig. 9 A schematic diagram showing an illumination device for a display screen having an optical element; and

[0078] Fig.10A schematic diagram of a display screen having an optical element operable in a first state corresponding to a restricted viewing mode and in a second state corresponding to a free viewing mode is shown.

[0079] The drawings are not drawn to scale and represent merely schematic representations. DETAILED DESCRIPTION

[0080] exist Figure 1a A schematic diagram of a first design of an optical element 1 in a first alternative is shown in FIG.

[0081] Therein, the second state of the exemplary optical element 1 is shown on the left side of the vertical dashed line, and the first state is shown on the right side thereof. The optical element comprises: (i) a substantially plate-shaped substrate S having a first (lower) large surface and a second (upper) large surface, wherein, for light incident on the optical element, the first large surface serves as a light incident surface and the other large surface serves as a light exit surface, (ii) a plurality of (permanently) opaque surfaces O1, O2, ... near or on the first large surface, (iii) in a first alternative, a plurality of surfaces S1, S2, ... that can be switched between opaque and transparent states near or on the second large surface, (iv) thereby: in a first state, the surfaces S1, S2, ... that can be switched in the first alternative are in an opaque state, and the optical element 1 limits the light incident on the light incident surface in its propagation direction, (v) and thereby in a second state, the surfaces S1, S2, ... that can be switched in the first alternative are in a transparent state, in which state the optical element 1 does not limit the light incident on the light incident surface in its propagation direction, but only prevents a portion of the light from being transmitted due to the opaque surfaces O1, O2, ...

[0082] In the first state, the restriction of the propagation direction is achieved by the mutual cooperation of the switchable surfaces S1, S2, ... switched to opaque at that time and the permanently opaque surfaces O1, O2, ..., as shown on the right side in the diagram of FIG. 1. A sufficiently inclined light beam that passes through the gaps between the opaque surfaces o1, O2, ... and penetrates into the substrate S is absorbed by the switchable surfaces S1, S2, ... switched to opaque. On the contrary, the light beam that propagates in a limited angle range passes through the transparent gaps between the opaque surfaces O1, O2, ..., so that the light that passes through the optical element 1 is restricted in its propagation direction. The shape and arrangement of the respective permanently opaque surfaces O1, O2, ... and the switchable surfaces S1, S2, ... and other parameters such as the refractive index of the transparent substrate S and its thickness determine which restrictions the propagation direction is subject to, in particular, at what angles and in which directions the light is transmitted, and whether the restriction of the propagation direction occurs only in one plane (for example, horizontal) or in multiple planes (for example, horizontal and vertical).

[0083] In addition, in a first alternative, in a first state of the optical element 1, there is typically a maximum transmittance in one or more directions parallel to the (imaginary) connecting line of the surface centers of the corresponding intermediate surfaces between each two switchable surfaces S1, S2, ... and the surface centers of the corresponding intermediate surfaces between the adjacent (permanently) opaque surfaces O1, O2, ...

[0084] In the second state, when the switchable surfaces S1, S2, ... are switched to transparent, in principle all light beams in the substrate S that are incident between the permanently opaque surfaces O1, O2, ... can also pass through the second large surface of the substrate S again and be emitted therefrom. Here, there is no restriction on the propagation direction. Only light beams that are irradiated from below to the permanently opaque surfaces O1, O2, ... and are not transmitted cannot be emitted from the second large surface of the substrate S. However, the permanently opaque surfaces O1, O2, ... can also be specularly emitted from below, so that the light incident thereon is reflected and can be recycled when necessary, for example when a backlighting device, for example, having a light guide, is located below it.

[0085] The light path through the optical element 1 is Figure 1a (and up to and including Figure 5 These are just a few selected conceivable beams, although in reality there are quite a few beams.

[0086] It preferably applies that within an angle range of greater than 30° (this angle can also vary, for example 10°, 20°, 25°, 40° or 45°) with respect to the surface normal of the second large surface of the substrate S and measured in a selectable direction perpendicular to the longitudinal extension of the substrate S, preferably measured in the horizontal direction, the angle-dependent transmission in the second state is greater than 30%, preferably greater than 50%, and in the first state it is less than 5%, preferably less than 3%, particularly preferably less than 2%. In the first state, the propagation direction of the light penetrating the optical element 1 (except for a small remainder) is significantly restricted.

[0087] The (permanent) opaque surfaces O1, O2, ... are preferably designed in the form of strips. However, it is also feasible that the opaque surfaces O1, O2, ... are distributed over (or near) the entire first large surface in a two-dimensional pattern (e.g., a grid-like pattern), which two-dimensional pattern can be periodic or non-periodic. Accordingly, in a first alternative, when the opaque surfaces O1, O2, ... are in the form of strips, the switchable surfaces S1, S2, ... are designed in the form of strips. In addition, the switchable surfaces S1, S2, ... have a shape similar or identical to the opaque surfaces O1, O2, ...

[0088] Figure 1bA schematic diagram of a second design of the optical element 1 in the first alternative is shown. This is achieved as follows: in the first alternative, the switchable surfaces S1, S2, ... include fluid chambers R, each containing a liquid F, the liquid F containing up to 30% by volume, preferably up to 20% by volume, of particles P that can move electrophoretically or magnetophoretically, the particles absorbing light of one or more wavelengths or wavelength ranges, wherein an electromagnetic switching mechanism is constructed in a planar manner on one or more sides of the fluid chamber R, and the electromagnetic switching mechanism, when in the switched-on state, generates an effective electromagnetic field in the fluid chamber R, whereby the particles P can move in the liquid, so that the position and / or orientation of the particles can be switched between at least two of the states, which produce opaque and transparent states of the switchable surfaces S1, S2, ... In the case of the first state, as in Figure 1b As shown on the right in FIG. 1 , the particles P are preferably distributed as much as possible over the entire surface of the switchable surfaces S1, S2, ..., while in the second state, the particles P are gathered in one or more volumes as small as possible, as in Figure 1b In the illustration on the left, this is done so as not to cover as large an area as possible of the switchable surfaces S1 , S2 , . . . .

[0089] The wavelength or wavelengths or wavelength ranges at which the electrophoretically or magnetophoretically movable particles P absorb light are preferably in the visible spectrum and particularly preferably cover the visible spectrum substantially completely. However, for special purposes, the wavelength or wavelength range may also be outside the visible spectrum, for example, if ultraviolet or infrared light is to be affected, for example for measurement technology purposes.

[0090] The electromagnetic switch mechanisms constructed in a planar manner on one or more sides of the fluid chamber R in the substrate S are arranged, for example, on the narrow side or large surface of the corresponding fluid chamber R. These electromagnetic switch mechanisms are not shown in the figure. For example, it is also possible to arrange these electrodes in a strip shape on the large surface of at least one fluid chamber R and with periodically alternating polarities in the second state, and to arrange the planar electrodes on the opposite large surface, which are also controlled according to the state.

[0091] The particles P are, for example, nanoparticles, quantum dots and / or dyes. The particles have a spatial extension of at most 200 nm, preferably at most 100 nm, particularly preferably at most 50 nm. The spatial extension is the maximum extension in three-dimensional space or the hydrodynamic radius, whichever is greater. For spherical particles P, this is the diameter. For rope-shaped particles, this is the maximum possible distance that two points on the surface of the particle P can have from one another.

[0092] The liquid F can be polar or non-polar. The liquid can also consist of, for example, water, oil, toluene or formaldehyde, also admixed with 10% by volume of ferrofluid and / or electrolyte. Other configurations are contemplated within the scope of the invention.

[0093] In addition, either the particles P are charged and the electromagnetic switching mechanism is designed as an electrode for generating a static or dynamic electric field, or the particles P are magnetic and the electromagnetic switching mechanism is designed as an electromagnetic layer for generating a static electric field or a dynamic magnetic field, so that the electromagnetic particles P move in the electric field or magnetic field in the liquid F.

[0094] For example, the width of the fluid chambers R in a plane parallel to the main propagation direction of the substrate S (the distance from the long side of the fluid chamber to the long side) can be between 2 μm and 50 μm and can be spaced apart from each other by at least 10 μm to 150 μm (the distance from the long side to the adjacent long side of the adjacent fluid chamber). The depth of the fluid chamber can be a few micrometers to about 50 micrometers. However, values ​​other than those presented here are obviously also feasible.

[0095] Furthermore, the switchable surfaces S1, S2, . . . can be divided into at least two groups, which can each be switched independently of one another, so that local switchability between the first state and the second state is achieved on the optical element 1.

[0096] exist Figure 2 A schematic diagram of a third design of an optical element 1 in the first alternative is shown in FIG. 1 . The second state of the exemplary optical element 1 is shown on the left by a vertical dashed line, and the first state is shown on the right. Here again, absorbent particles P are used, such as Figure 1b The main difference here is that the electrodes are designed in such a way that in the second state the particles P are concentrated as much as possible in the smallest possible volume in the fluid chamber R. This can be achieved, for example, by arranging the electrodes on the right narrow side of the fluid chamber R, in which the electrodes are manipulated in the second state so that the particles P move therein.

[0097] In a first alternative of the optical element 1, the optical element may also include a mechanism for suppressing a light beam propagating in the substrate S, which light beam penetrates into the substrate S either from the gap between two adjacent opaque surfaces O1, O2 or from the gap between two adjacent switchable surfaces S1, S2 in the opaque state of the switchable surfaces S1, S2, ... and is directed to the corresponding switchable surfaces S3, S4 on the respective opposite large surfaces of the substrate S or to the non-adjacent gap between the opposite opaque surfaces O3, O4. The mechanism may be designed, for example, in such a way that, due to a suitable choice of the refractive index of the substrate S compared to the refractive index of the medium surrounding the substrate, a certain light beam at a determinable angle does not leave the substrate due to total reflection.

[0098] Alternatively, the mechanism can be formed in the following manner, respectively, between some or all of the opaque surfaces O1, O2, ..., absorbers are embedded in the substrate S, and the absorbers extend substantially from the first large surface of the substrate to the second large surface and are oriented approximately perpendicular to one of the large surfaces. In addition, the mechanism can be implemented in the following manner, that is, the thickness of the opaque surfaces O1, O2, ... and / or the switchable surfaces S1, S2, ... are appropriately selected. A plurality of the above-mentioned measures for implementing the mechanism can also be combined with each other.

[0099] also, Figure 3 A schematic diagram of a first design of an optical element 1 in a second alternative is shown. Here, the optical element (i) comprises: a substantially plate-shaped substrate S having a first (upper) large face and a second (lower) large face, in this example, for light incident on the optical element, the first large face serves as a light incident face and the other large face serves as a light exit face, (ii) a plurality of opaque faces O1, O2, ... near or on the first large face, (iii) a plurality of chambers K1, K2, ... in the substrate S in the second alternative, the chambers being filled with a liquid F, wherein the liquid F contains electrophoretically or magnetophoretically movable particles P in a maximum of 30% by volume, preferably a maximum of 20% by volume, the particles absorbing light of one or more wavelengths or wavelength ranges, and the particles being positioned in the corresponding chambers K1, K2 by a variable electromagnetic field in at least two different states. 2..., (iv) so that: in the first state, in the second alternative, more than half of all the particles P, particularly preferably more than 90% of all the particles P are located in the half, preferably one third, of the corresponding chambers K1, K2... facing away from the first large surface, and the optical element 1 limits the propagation direction of the light incident on the light incident surface, (v) and so that in the second state, in the second alternative, more than half of all the particles P, particularly preferably more than 90% of all the particles P are located in the half of the corresponding chambers K1, K2... facing the first large surface, and the optical element 1 does not limit the propagation direction of the light incident on the light incident surface, but due to the opaque surfaces O1, O2,...

[0100] The above-described embodiments for the electrophoretically or magnetophoretically movable particles P apply accordingly and should not be repeated here for reasons of redundancy. In order to better distinguish between the first and second alternatives, in the second alternative, the chambers K1, K2, ... present therein, which are filled with liquid F, are referred to as "chambers", although in practice they also correspond to fluid chambers. In addition, for Figure 1a The explanation given by et al. is similarly applicable to the restriction of the propagation direction of light. Figure 3 The image is also symbolically represented by a beam of light incident from below.

[0101] In the second alternative of the optical element 1, it is preferably applicable that: each of the chambers K1, K2, ... is located above the opaque surfaces O1, O2, ... in the projection direction perpendicular to the substrate S, and the basic surface shape of such chambers K1, K2, ... roughly corresponds to the shape of such opaque surfaces O1, O2, .... In addition, it is advantageous that: in the second alternative, an electromagnetic switch mechanism is constructed in a planar shape on one or more sides of the chambers K1, K2, ..., and the electromagnetic switch mechanism, when turned on, generates an electromagnetic field effective in the chambers K1, K2, ..., whereby the particles P move in the liquid so that the position and / or orientation of the particles P can be switched between at least two states, and the states generate two states of the at least optical element. The electromagnetic switch mechanism is preferably an electrode, wherein the electrode on at least the second large surface is (at least partially) transparent. The electrodes on the first large surface are arranged on or near the opaque surfaces O1, O2, ..., or if the electrodes are opaque electrodes, they can even correspond to these surfaces.

[0102] With regard to the dimensions of the chambers K1, K2, ... in the second alternative, reference is made to the design variants of the fluid chamber R given above for the first alternative of the optical element. In particular, however, the depth of such chambers K1, K2, ... can also be greater than 50 μm, for example 100 μm.

[0103] The general design of the liquid F and the particles P as previously given for the first alternative can also be similarly applied to the second alternative, which makes it unnecessary to repeat the description here. The significant difference between the configuration according to the first alternative and the second alternative is that in the first alternative, the particles P make the corresponding switchable surface S1, S2, ... switch to be completely opaque in one state and switch to be as transparent as possible in another state, and the particles P move horizontally, while in the second alternative, the particles P between the two states move vertically in order to achieve or avoid the desired influence on the light propagation direction by cooperating with the opaque surfaces O1, O2, ...

[0104] For the optical element 1 in the second alternative, in the first state, at least four fifths, particularly preferably more than nine tenths, of all the particles P are located in the one third, preferably one quarter, of the second largest surface of the corresponding chambers K1, K2, . . . adjacent to the substrate S.

[0105] A particularly advantageous design of the optical element 1 in the second alternative is that the spaces between the respective adjacent chambers K1, K2, ... in the substrate S have a higher refractive index than the liquid F in the chambers K1, K2, ..., wherein this applies at least to one wavelength in the visible light range, but preferably to all wavelengths in the range from 400 nm to 800 nm. Figure 4 , a schematic diagram of a second design of an optical element 1 according to a second alternative is shown.

[0106] This ensures that, for example, light irradiating the optical element 1 on the first large surface enters the optical element only through a portion of the surface of the first large surface between the opaque layers O1, O2, ..., and there, depending on the incident direction, polarization and the above-mentioned refractive index difference, a) is totally reflected between the two chambers K1, K2, ..., and then coupled out again on the upper surface of the corresponding area of ​​the substrate S (here, on the second large surface) (case a), or b) overcomes the refractive index limit of the substrate material to the liquid F and enters an adjacent chamber with the liquid F, propagates in the chamber, and finally on the upper side of the chamber. Based on the particles P in the first state being absorbed, or being coupled out when the second state exists (case b), or c) after overcoming the refractive index boundary from the substrate material to the liquid F, overcoming the next refractive index boundary from the liquid F to the adjacent substrate material, and being coupled out or continuing to propagate in the first optical element according to the propagation direction and polarization given at that time, until the light is coupled out or absorbed according to the state of the optical element 1 (case c), or d) in these two states, the substrate S passes between the two chambers K1 and K2 without total reflection, and is coupled out again from the optical element 1 on the second large surface (case d). In this form of physical implementation of the present invention, not all cases a) to d always necessarily occur. For example, case c) may not occur, such as Figure 4 The selected light beams of cases a), b) and d) are marked there. This description is similarly applicable to the case where light is irradiated onto the optical element 1 via the second large face, because the light path is reversible.

[0107] The above-defined differences in the refractive indices according to their effects can in principle also be used for the first alternative of the optical element, which has already been described with reference to Figure 1a , Figure 1b and Figure 2 This is explained by way of example in three designs: Then, instead of the chambers K1, K2, ... according to the second alternative, in the first alternative, those volume regions of the substrate S which have a lower refractive index than the surrounding volume regions are located between the opaque surface O1, ... and the immediately adjacent switchable region S1, ... In principle, the situations a) to d) can thus also be generated there or selected from them.

[0108] The advantage of the second design of the second alternative is that the light confined in its propagation direction by the optical element 1 in the first state has an approximately top-hat distribution, i.e. around the preferred propagation direction the brightness has only a low angular dependence and subsequently the transmittance drops sharply. The described transmittance dependence has the advantage that an observer from the preferred direction perceives the transmittance uniformly and from an angle of, for example, greater than 30° (this angle can also vary, for example 10°, 20°, 25°, 40° or 45°), the transmittance is greatly reduced for the observer.

[0109] An advantageous design is also produced in the following way: each opaque surface O1, O2, ... is formed by a permanent absorption layer and / or by at least one downwardly reflecting layer. If only one reflecting layer is present here (which is possible within the scope of the invention), then this reflecting layer will of course also have opaque properties. For example, when the optical element 1 is installed in a lighting device (for example for an LCD panel), the reflective properties help to increase the efficiency.

[0110] In two alternatives of the optical element, the substrate S can form a cover substrate for an OLED, microLED or LCD panel, each panel having pixels or sub-pixels. Alternatively, the substrate S can be applied to the cover substrate or positioned in front of it.

[0111] It is advantageous for the first alternative that the surface center of each area between the switchable surfaces S1, S2, ... and / or the opaque surfaces O1, O2, ... is located in front of the center of the pixel or sub-pixel of the corresponding panel in a vertical projection toward the substrate S with a tolerance of at most 20% of the width of each such area.

[0112] However, it is also possible that the surface center of each area between the switchable surfaces S1, S2, ... and / or the opaque surfaces O1, O2, ... is placed slightly offset in front of the center point of the pixel or sub-pixel of the corresponding panel in the vertical projection toward the substrate S, so that the imaginary connecting line of the corresponding surface center of the switchable surfaces S1, S2, ... and the surface center of the opaque surfaces O1, O2, ... points to the observer B (at least for one plane, such as a plane perpendicular to the second largest surface of the substrate S, which imaginarily intersects with the eyes of the observer B) with a maximum tolerance of 15°. Therefore, the light transmitted in the first state of the optical element 1 is focused on the observer B. This point is Figure 5 It is shown in a very simplified form. For the appropriate dimensioning, the beam groups must be applied accordingly. Of course, in practice, not only six opaque surfaces O1, O2, ... and six switchable surfaces S1, S2, ... will be used, but a plurality of these surfaces will be used.

[0113] Changes in the area sizes of the switchable areas S1, S2, ... (see Figure 6 ) and / or opaque surfaces O1, O2, ... (see Figure 7 ) can further affect the transmission characteristics of the optical element 1.

[0114] In this sense, in a second alternative, for example, the upper surface of the chambers K1, K2, ... can be smaller than the lower (bottom) surface of the chambers K1, K2, ..., wherein the lower surface usually corresponds to or is congruent with the opaque surfaces O1, O2, .... As a result, the transmittance is again focused on the viewer B. Figure 8 This is shown in a very simplified form.

[0115] also, Fig. 9 A schematic diagram of an illumination device for a display screen having an optical element 1 is shown, which can be operated in a first state corresponding to a restricted viewing mode and in a second state corresponding to a free viewing mode. This includes a planarly extending backlighting device BLU emitting light in an unrestricted angular range and the optical element 1 located in front of the backlighting device BLU in the viewing direction, as described above.

[0116] The backlighting device BLU used here preferably emits light in an unlimited angle range. However, it is also possible that the backlighting device BLU has a certain prefocus, for example by not emitting more than 10% or 20% of the peak brightness horizontally in an angle range (measured horizontally) exceeding 30° or 45°.

[0117] Such an illumination device is advantageously used together with a transmissive image display unit (e.g. an LCD panel) arranged in front of the optical element 1 in the viewing direction in order to obtain a display screen operating in a first state corresponding to a restricted viewing mode and in a second state corresponding to a free viewing mode, since the light from the illumination device BLU is sometimes restricted in the propagation direction due to the optical element 1, i.e. focused (first state) and sometimes unfocused (second state).

[0118] at last, Fig.10 A schematic diagram of a display screen having an optical element 1 is shown, which can be operated in a first state corresponding to a restricted viewing mode and in a second state corresponding to a free viewing mode. Such a display screen comprises: an optical element 1 (as described above), and an image display unit 2 (in the case of a display screen) located in front of or behind the optical element 1 from the viewer's perspective. Fig.10 , a variation in which the image display unit 2 is arranged at the rear is shown).

[0119] The image display unit 2 is, for example, an OLED display, an LCD panel, a SED panel, a FED panel, a microLED display, or a VFD. Since the optical element 1 is effective regardless of the type of the image display unit 2, any other type of image display unit may also be considered.

[0120] In a first state of the optical element 1 , a restricted viewing mode results for the display screen in question, and in a second state of the optical element 1 a free viewing mode results.

[0121] Means for reducing or controlling reflections, such as anti-glare and / or anti-reflection coatings, may be arranged on the upper side of the image display unit 2 .

[0122] The optical element described above and the lighting device described and the display screen that can be realized therewith achieve the set objects: An optical element has been described that can influence the transmittance as a function of the angle and can be switched between at least two states. The optical element can be realized cost-effectively and can be used in particular with different types of display screens in order to be able to switch between a protected viewing mode and a free viewing mode. A display screen based on the optical element and a lighting device for the display screen are also described.

[0123] The invention described above can be advantageously used anywhere confidential data is displayed and / or entered, such as when entering a PIN or for displaying data at an ATM or payment terminal or for password entry or when reading emails on a mobile device. As mentioned above, the invention can also be used in passenger cars.

[0124] Reference numerals list

[0125] 1 Optical components

[0126] 2 Image display unit

[0127] BLU Backlighting Unit

[0128] F Liquid

[0129] K1, K2, ... chamber

[0130] O1, O2, ... Opaque surface

[0131] P particles

[0132] R Fluid Chamber

[0133] S substrate

[0134] S1, S2, ... Switchable surfaces

Claims

1. An optical element (1), comprising: A substantially plate-shaped or shell-shaped substrate (S), the substrate having a first and a second large surface, wherein one large surface is used as a light incident surface for light incident on the optical element (1), and the other large surface is used as a light exit surface for light incident on the optical element (1). Multiple opaque surfaces (O1, O2...) located on the first large surface, a plurality of surfaces (S1, S2, ...) on the second large surface which can be switched between an opaque and a transparent state, wherein a transparent intermediate surface is respectively located between every two opaque surfaces (O1, O2, ...) and between every two switchable surfaces (S1, S2, ...), The switchable surfaces (S1, S2, ...) are respectively located above the opaque surfaces (O1, O2, ...) in the projection direction perpendicular to the substrate S. The optical element (1) limits the propagation direction of light incident on the light incident surface in a first state, and in the first state, the switchable surfaces (S1, S2, ...) are in an opaque state, wherein the maximum transmittance exists in a direction parallel to a line connecting the center of a corresponding intermediate surface between two corresponding switchable surfaces (S1, S2, ...) and the center of a corresponding intermediate surface between the nearest opaque surfaces (O1, O2, ...), and In the second state, the optical element (1) does not restrict the propagation direction of light incident on the light incident surface, but only a part of the light cannot be transmitted due to the opaque surfaces (O1, O2, . . .). In the second state, the switchable surfaces (S1, S2, . . .) are in a transparent state.

2. The optical element (1) according to claim 1, characterized in that The switchable surfaces ( S1 , S2 , . . . ) contain at least one electrochromic layer, an LC cell and / or an LC film with dichroic dyes.

3. The optical element (1) according to claim 1, characterized in that The switchable surface (S1, S2, ...) includes a fluid chamber (R) containing a liquid (F), wherein the liquid (F) contains up to 30% by volume of particles (P) that can move electrophoretically or magnetophoretically, and the particles absorb light of one or more wavelengths or wavelength ranges, wherein an electromagnetic switching mechanism is also constructed in a planar manner on one or more sides of the fluid chamber (R), and when the electromagnetic switching mechanism is turned on, it generates an effective electromagnetic field in the fluid chamber (R), thereby allowing the particles (P) to move in the liquid, so that the position and / or orientation of the particles can be switched between at least two states, and the particles produce the above-mentioned opaque and transparent states of the switchable surface (S1, S2, ...).

4. The optical element according to any one of claims 1 to 3, characterized in that: The switchable surfaces ( S1 , S2 , . . . ) are divided into at least two groups which are each switchable independently of one another, so that local switchability between a first state and a second state is achieved.

5. The optical element (1) according to any one of claims 1 to 3, further comprising: A mechanism for suppressing a light beam propagating in the substrate (S), the light beam either being incident into the substrate (S) from a gap between two adjacent opaque surfaces (O1, O2) or from a gap between two adjacent switchable surfaces (S1, S2) in the opaque state of the switchable surfaces (S1, S2, ...), and being directed to corresponding non-adjacent gaps between corresponding switchable surfaces or opaque surfaces on respectively opposing large surfaces of the substrate (S).

6. The optical element (1) according to any one of claims 1 to 3, characterized in that: The substrate (S) is a cover substrate of an OLED panel, a cover substrate of a microLED panel, or a cover substrate of an LCD panel, each of which has pixels or sub-pixels.

7. The optical element (1) according to claim 6, characterized in that The surface center of each area between the switchable surfaces (S1, S2, ...) and / or the opaque surfaces (O1, O2, ...) is located in front of the center of the pixel or sub-pixel of the corresponding panel with a tolerance of maximum 20% of the width of each of the said areas when vertically projected onto the substrate (S).

8. The optical element (1) according to any one of claims 1 to 3, characterized in that The opaque surfaces (O1, O2, . . . ) are arranged on or near a large surface behind the substrate (S) along the viewing direction of the observer, and specular reflection or partial specular reflection occurs on the side of the opaque surfaces facing away from the observer.

9. An optical element (1), comprising: A substantially plate-shaped or shell-shaped substrate (S), the substrate having a first and a second large surface, wherein one large surface is used as a light incident surface for light incident on the optical element (1), and the other large surface is used as a light exit surface for light incident on the optical element (1). Multiple opaque surfaces (O1, O2...) located on the first large surface, A plurality of chambers (K1, K2, ...) located in a substrate (S), the chambers being filled with a liquid (F), wherein the liquid (F) contains up to 30% by volume of particles (P) that can move electrophoretically or magnetophoretically, the particles being able to absorb light of one or more wavelengths or wavelength ranges and being able to be positioned in the respective chamber (K1, K2, ...) by means of an electromagnetic field that can be varied in at least two different states, wherein a transparent intermediate surface is respectively present between each two opaque surfaces (O1, O2, ...) and between each two chambers (K1, K2, ...), The chambers (K1, K2, ...) are respectively located above the opaque surfaces (O1, O2, ...) in the projection direction perpendicular to the substrate S. The optical element (1) limits the propagation direction of light incident on the light incident surface in the first state, and in the first state, more than half of all the particles (P) are located in the half of the corresponding cavity (K1, K2, ...) facing away from the first large surface, wherein the maximum transmittance exists in the direction parallel to the line connecting the surface center of the corresponding intermediate surface between the corresponding two switchable surfaces (S1, S2, ...) and the corresponding surface center of the intermediate surface between the adjacent cavities (K1, K2, ...), and In the second state, the optical element (1) does not restrict the propagation direction of the light incident on the light incident surface, but only a part of the light cannot be transmitted due to the opaque surface (O1, O2, ...). In the second state, more than half of all the particles (P) are located in the half of the corresponding chamber (K1, K2, ...) facing the first large surface.

10. The optical element (1) according to claim 9, characterized in that The substrate (S) is a cover substrate of an OLED panel, a cover substrate of a microLED panel, or a cover substrate of an LCD panel, each of which has pixels or sub-pixels.

11. The optical element (1) according to claim 9, characterized in that The opaque surfaces (O1, O2, . . . ) are arranged on or near a large surface behind the substrate (S) along the viewing direction of the observer, and specular reflection or partial specular reflection occurs on the side of the opaque surfaces facing away from the observer.

12. The optical element (1) according to claim 9, characterized in that An electromagnetic switching mechanism is constructed in a planar manner on one or more sides of the chamber (K1, K2, ...), and when the electromagnetic switching mechanism is turned on, it generates an effective electromagnetic field in the chamber (K1, K2, ...), thereby allowing particles (P) to move in the liquid, so that the position and / or orientation of the particles (P) can be switched between at least two states, and the at least two states realize the above-mentioned at least two states of the optical element (1).

13. The optical element (1) according to claim 9, characterized in that In the first state, at least four fifths of all particles (P) are located in that third of the respective chamber (K1, K2, . . . ) which is adjacent to the second largest area of ​​the substrate (S).

14. The optical element (1) according to claim 9, characterized in that The interspaces between respectively adjacent chambers ( K1 , K2 , . . . ) have a higher refractive index than the liquid (F), with this applying to all wavelengths in the range from 400 nm to 800 nm.

15. An illumination device for a display screen, the display screen being capable of operating in a first state corresponding to a restricted viewing mode and in a second state corresponding to a free viewing mode, the illumination device comprising: A planarly extending backlight unit (BLU) capable of emitting light at an unlimited range of angles, and The optical element (1) according to any one of claims 1 to 14, wherein the optical element is located in front of the backlighting unit (BLU) in the viewing direction.

16. A display screen capable of operating in a first state corresponding to a restricted viewing mode and in a second state corresponding to a free viewing mode, the display screen comprising: The optical element (1) according to any one of claims 1 to 14, and The image display unit (2) is located in front of or behind the optical element (1) from the observer's point of view.

Images