Switchable optical filter, lighting device and screen

Abstract

The invention relates to a switchable optical filter (5) comprising: a first optical element (1) comprising: a plurality of light-absorbing transition dipole moments wherein a transition dipole moment of a relative proportion p (0.6 < = p < = 1.0) of all transition dipole moments is oriented parallel to a first preferred direction, optionally for the first optical element (1), with a tolerance of maximum 15 DEG; means for selectively generating a first electric field (EF1) or a second electric field (EF2); a liquid crystal layer (3) arranged behind or in front of the first optical element (1) in the viewing direction, the first electric field (EF1) or the second electric field (EF2) acting on the liquid crystal layer and thereby influencing the polarization state of light penetrating the liquid crystal layer, the absolute value of the first electric field (EF1) differing from the absolute value of the second electric field (EF2) by at least 0.1 MV / m, and the absolute value of the second electric field (EF2) differing from the absolute value of the first electric field (EF1) by at least 0.1 MV / m. The switchable filter (5) has a first electric field (EF1) and a second electric field (EF2) such that a transmission characteristic of the switchable filter (5) differs between a first operating mode B1 to which the first electric field (EF1) is applied and a second operating mode B2 to which the second electric field (EF2) is applied.

Description

Technical Field

[0001] Significant progress has been made in recent years in expanding the viewing angles of LCDs. However, the extremely large viewing area of ​​a screen often becomes a disadvantage. Increasingly, information, such as banking data or other personal information, as well as sensitive data, can be provided on mobile devices like laptops and tablets. Accordingly, people need to control who can see this sensitive data; they need the ability to choose a wide viewing angle—a public mode—to share information on the display with others, such as when viewing holiday photos or even for advertising purposes. On the other hand, a smaller viewing angle—a private mode—is needed to maintain the privacy of the image information.

[0002] A similar problem exists in the automotive manufacturing industry: once the engine is started, drivers cannot afford to be distracted by visual content such as digital entertainment programs, while passengers expect to be able to watch content while driving. Therefore, a screen that can switch between corresponding presentation modes is needed.

[0003] Micro-visor-based supplementary films have been used in mobile displays to provide visual data protection. However, these films are not switchable or convertible; they must always be applied by hand and then removed. They also must be shipped separately from the display when not in use. Another major drawback of using this type of sheet film is light loss. Background Technology

[0004] US 6,765,550 B2 describes this type of privacy achieved through micro blinds. The biggest drawback of this solution is the mechanical removal and attachment of the filter, as well as the light loss in the protection mode.

[0005] US 5,993,940 A describes the use of a thin film with small strip-shaped prisms uniformly distributed on its surface to achieve a privacy mode, i.e., a restricted viewing mode with a small field of view. The research and manufacturing of this technology presents considerable technical challenges.

[0006] US 2013 / 0308185 A1 describes a special light guide with stepped sections that emits light in different directions on a large surface, depending on the direction from which the light guide is illuminated starting from the narrow surface. When used in conjunction with a transmissive image reproduction device (such as an LC display), it can create a screen that can switch between free viewing and restricted viewing modes. Its main drawback is that the restricted viewing effect can only be produced on the left / right or up / down, but not simultaneously on both sides, which is necessary for certain payment processes, for example. Furthermore, even in restricted viewing mode, residual light can still be seen from the obstructed viewing angle.

[0007] The applicant's WO 2015 / 121398 A1 describes a screen with two operating modes, wherein scattering particles are present in the volume of the corresponding light guide to achieve the switching between operating modes. However, the polymer scattering particles chosen in this case generally have the following drawbacks: light is output coupled from two large surfaces, so approximately half of the useful light is emitted in the wrong direction, i.e., towards the backlight direction, and due to structural reasons, it cannot be sufficiently recovered at that location. Furthermore, depending on the situation, especially at higher concentrations, the polymer-based scattering particles distributed in the volume of the light guide may cause scattering effects, which will weaken the privacy protection effect in the protected operating mode.

[0008] The methods and configurations described above generally have the following drawbacks: they significantly reduce the basic screen brightness, and / or require complex and expensive optical components for mode switching, and / or reduce the resolution in public modes for free viewing, and / or cause visual artifacts when using displays with extremely high resolution, and / or cannot be used for self-emissive screens such as OLEDs. Summary of the Invention

[0009] Therefore, the object of the present invention is to describe a filter having optical elements, wherein light incident on the optical elements is transmitted or partially or completely absorbed according to its incident direction and polarization characteristics—(not primarily) according to its position. With such a filter, the transmission of light can be affected angularly—optionally perpendicularly relative to a seated or standing observer—whereby switching between at least two operating modes is possible. Specifically, the angular correlation ratio of the transmission behavior between the two operating modes should be defined. Furthermore, the filter should also be applicable to self-emissive screens (such as OLEDs).

[0010] In the first technical solution, the solution of the present invention to achieve the above objective is a switchable filter, comprising: The first optical element includes A large number of light-absorbing transition dipole moments are arranged in a single layer of at least 0.1 μm and a maximum of 40 μm, or in multiple separate layers with a total thickness of up to 40 μm (which may exist, depending on the case, in the adhesive layer between individual transition dipole moment layers or substrate layers, and is not included in this calculation). The transition dipole moment is preferably achieved using at least two dichroic dyes. Furthermore, of all transition dipole moments, the transition dipole moments with a relative proportion p (0.6 ≤ p ≤ 1.0, typically p < 1) are permanently or at least in the first state oriented or vary about a first preferred direction selectable for the first optical element with a tolerance of up to 15°, wherein the first preferred direction is arranged at a predetermined angle α to the central normal of the first optical element (e.g., α = 0°, α = ±2°, or a value (α) > 2°), wherein the angle α is measured in an optional first plane containing the aforementioned central normal, and wherein the aforementioned first plane is preferably parallel to the edge of the first optical element, such as the lower edge. This allows light incident on the first optical element in the direction of incidence and polarization state to be transmitted or at least partially absorbed according to its direction of incidence and polarization state relative to the first optical element. A device for selectively generating a first electric field EF1 or a second electric field EF2. A liquid crystal layer is arranged behind or in front of a first optical element along the observation direction. A first electric field EF1 or a second electric field EF2 acts on the liquid crystal layer and thereby affects the polarization state of light passing through the liquid crystal layer. The absolute values ​​of the first electric field EF1 and the second electric field EF2 differ by at least 0.1 MV / m. A first linear polarizing filter X located in front of the liquid crystal layer along the observation direction (if the liquid crystal layer is arranged in front of the first optical element along the observation direction). This causes the transmission characteristics of the switchable filter to differ between a first operating mode B1 where the first electric field EF1 is applied and a second operating mode B2 where the second electric field EF2 is applied, wherein at at least one point on the switchable filter (preferably at at least five points, more preferably distributed at multiple points on the entire surface of the switchable filter, or even on the entire surface of the filter), except for optional tolerances (e.g., 5% or 10%, or smaller or larger values), the corresponding relative transmittances under operating modes B1 and B2 are respectively expressed by a first transmittance T for the first operating mode B1. B1 (β) and the second transmittance T for the second operating mode B2 B2 (β) describes the transmittance, which is related to angle β and is normalized so that the transmittance value at a predetermined angle β=α is applicable to T. B1 (α) = 1 and T B2 (α) = 1, Therefore, linearly polarized light or elliptically polarized light with a major-to-minor axis ratio of at least 4:1 is: If the switchable filter is incident at an angle (β) of α-5°≤β≤α+5°, then T B1 (β) / T B2 The ratio of (β) is greater than 0.9 + log 10 (p) and less than 1.3 - log10 (p) If the switchable filter is incident at an angle (β) of α-30°≤β≤α-20° or α+20°≤β≤α+30°, then T B1 (β) / T B2 The ratio of (β) is greater than 2 · (1 + log) 10 (p)), and If the switchable filter is incident at an angle (β) of α-45°≤β≤α-35° or α+35°≤β≤α+45°, then T B1 (β) / T B2 The ratio of (β) is greater than 9 · (1 + 2 · log 10 (p)).

[0011] For the first optical element, in special applications, a second or even more other states can be achieved, for example, through a so-called object-subject liquid crystal cell.

[0012] A device for selectively generating a first electric field EF1 or a second electric field EF2 may, for example, refer to a transparent electrode made of indium tin oxide connected to an electronic control device.

[0013] In principle, the following should apply: within the angular range of β≤α-5° or α+5°≤β, the first transmittance T used for the first operating mode. B1 (β) is typically greater than the second transmittance T used in the second operating mode B2. B2 (β). As described below, this point is mainly achieved by selecting the first electric field EF1 and the second electric field EF2. The following implementation scheme shall apply: linearly polarized light or elliptically polarized light with a major semi-axis to minor semi-axis ratio of at least 4:1 is incident on the switchable filter, and its polarization is mostly parallel to the aforementioned first plane with a maximum tolerance of 5°.

[0014] Depending on the specific design of the liquid crystal layer—whether it be TN (Twisted Nematic), VA (Vertical Alignment), IPS (In-Plane Switching), FFS (Fringe Field Switching), or other possible types—if the liquid crystal layer is arranged behind the first optical element in the viewing direction, the first electric field EF1 is selected such that, after passing through the liquid crystal layer, the transmitted light has at least 40% of its electric field component perpendicular to the first plane, wherein its polarization is mostly perpendicular to the first plane (or at an optional angle within the range of 45° to 135°), with a maximum tolerance of 5°. The second electric field EF2 is selected such that, after passing through the liquid crystal layer, the transmitted light has at least 80% of its electric field component parallel to the first plane. Under the above premise, i.e., the incident light is mostly polarized parallel to the aforementioned first plane, with a maximum tolerance of 5°, the field strength of the second electric field EF2 can, for example, be 0 V / m, i.e., essentially zero electric field. The field strength of the first electric field EF1 can exceed 0.1 MV / m. This electric field is preferably an alternating field, changing its polarity in a rectangular or sinusoidal manner at a frequency on the order of at least 50 Hz, preferably at least 0.8 kHz, for example at 1.0 kHz. Frequencies higher than 1.0 kHz can also be used. In other words, in the second operating mode B2 with the second electric field EF2, a polarization state as pure as possible is generated because, after passing through the liquid crystal layer, the transmitted light has at least 80% of its electric field component parallel to the first plane. In contrast, in the first operating mode B1 with the first electric field EF1, the electric field component is mainly mixed or significantly rotated because, after passing through the liquid crystal layer, the transmitted light has at least 40% of its electric field component perpendicular to the first plane. This is achieved, for example, when the liquid crystal layer is in the form of an IPS cell or when circular polarization is used after the liquid crystal layer.

[0015] Alternatively, the first electric field EF1 can be zero, while the field strength of the second electric field EF2 exceeds 0.1 MV / m. Of course, both the first electric field EF1 and the second electric field EF2 can be non-zero.

[0016] If the liquid crystal layer is arranged in front of the first optical element along the observation direction, that is, a polarizing filter is typically also provided in front of the liquid crystal layer along the observation direction, then the aforementioned values ​​of the first electric field EF1 and the second electric field EF2 can also be used to generate operating modes B1 and B2. This structure is typically used in conjunction with a backlit transparent image reproduction device, wherein a switchable filter is located therebetween. In this technical solution, the first optical element transmits at least 90% of the s-polarized light at an angle greater than 20°. Thus, depending on the specific operating mode, at least 95% of the p- or s-polarized light is generated relative to the first plane, and subsequently, depending on the specific orientation of the polarizing filter, which may be part of the aforementioned image reproduction device, this light is mostly absorbed or transmitted at an angle greater than 20°.

[0017] The essence of this invention lies in the fact that the selection of the transition dipole moment with a relative proportion p among all transition dipole moments, combined with the different selections of the first electric field EF1 and the second electric field EF2 and the resulting polarization effect, can satisfy the above inequality. This inequality provides a comparison of the aforementioned angular correlation of transmittance. Furthermore, as described below, the use of thick layers of transition dipole moments leads to a tightening of the inequality: In a preferred embodiment, the first optical element comprises a large number of light-absorbing transition dipole moments arranged in a single layer with a thickness of at least 1 μm and a maximum of 40 μm, or arranged in multiple separate layers with a total thickness of at least 1 μm and a maximum of 40 μm for the transition dipole moments (which may exist, depending on the situation, in the adhesive layer between individual transition dipole moment layers or substrate layers, not included here). Thus, linearly polarized light or elliptically polarized light with a major-to-minor axis ratio of at least 4:1 is: If the switchable filter is incident at an angle (β) of α-5°≤β≤α+5°, then T B1 (β) / T B2 The ratio of (β) is greater than 1.0 + log 10 (p) and less than 1.3 - log 10 (p), If the switchable filter is incident at an angle (β) of α-30°≤β≤α-20° or α+20°≤β≤α+30°, then T B1 (β) / T B2 The ratio of (β) is greater than 3 · (1 + log) 10 (p)), and If the switchable filter is incident at an angle (β) of α-45°≤β≤α-35° or α+35°≤β≤α+45°, then T B1 (β) / T B2 The ratio of (β) is greater than 16 · (1 + 2 · log 10 (p)).

[0018] One important aspect of this approach lies in the fact that, by switching between a first operating mode B1 (where a first electric field EF1 is applied) and a second operating mode B2 (where a second electric field EF2 is applied, and the absolute values ​​of the first and second electric fields EF1 and EF2 differ by at least 0.1 MV / m), according to a specific technical solution, only in one operating mode (such as the first operating mode B1) is the p-polarized light incident on the liquid crystal layer substantially converted into s-polarized light, which then enters the first optical element and is also transmitted at an angle greater than 20°. Conversely, according to a specific technical solution, only in another operating mode (such as the second operating mode B2) is the s-polarized light incident on the liquid crystal layer substantially converted into p-polarized light, which then enters the first optical element and is also absorbed at an angle greater than 20°. Ultimately, the aforementioned transmittance T... B1 (β) / T B2 (β) holds true within the given angular range.

[0019] If the transition dipole moment for absorption is also composed of a dichroic dye, wherein the dye mass density is typically greater than 1%, this helps to satisfy the inequality for the given reasonable transmittance.

[0020] It can also be explicitly stated that other operating modes B3, B4, etc., are provided, whose electric fields EF3, EF4, etc., differ from those of electric fields EF1 and EF2. Furthermore, operating modes B1, B2, etc., may also differ locally on the switchable filter. The latter indicates that the first optical element (and each other such optical element, if present) and / or the liquid crystal layer and / or the means for selectively generating the first electric field E1 or the second electric field E2 are divided into multiple individually switchable segments, so that local switching between the corresponding possible operating modes is possible.

[0021] Normalized T for transmittance B1 (α) = 1 and T B2 (α) = 1, and the following should be noted: Of course, angles β and α are measured in the same plane mentioned above. In principle, T B1 (α) > 1 and / or T B2 (α) > 1 also applies to angle β ≠ α. In many cases, T B1 (α) < 1 and / or T B2 (α) < 1 also applies to angle β ≠ α.

[0022] In cases where the transition dipole moment can change, for example, by rotation within a so-called guest-subject liquid crystal cell, this guest-subject liquid crystal cell can directly correspond to the aforementioned liquid crystal layer, but it is not necessary to do so.

[0023] In a preferred embodiment, when a second electric field EF2 is applied, light penetrating the liquid crystal layer is transmitted substantially unchanged, while when a first electric field EF1 is applied, the incident light is circularly polarized or ellipsoidally polarized, or its polarization is rotated by 90°. In essence, this indicates that at the interface, the orientation of the liquid crystal molecules is determined by the electric field and surface induction forces; therefore, the liquid crystal molecules are not ideally oriented, resulting in a slight, undesirable change in polarization.

[0024] Regarding TN liquid crystal technologies, the following applies: On the large surface confining the liquid crystal layer, the orientation of liquid crystal molecules typically differs by 90°. This orientation can be aided by PMI or PVA and additional mechanical or optical treatments to the surface. Furthermore, for TN liquid crystal layers, the following typically applies: When switching between electric fields EF1 and EF2, most of the liquid crystal in the layer rotates off-plane by 75 to 90 degrees. For IPS and FFS liquid crystal layers, the rotation of LC molecules is typically less than 45°, usually around 20° to 40°.

[0025] If the liquid crystal layer is arranged behind the first optical element along the viewing direction, linearly polarized or elliptically polarized light is preferably incident, wherein the ratio of the major semi-axis to the minor semi-axis is at least 4:1 (preferably at least 5:1 or greater). This can be achieved, for example, through a linearly polarizing filter in the optical path, or through a λ / 4 layer in the case of circularly polarized light.

[0026] In another technical solution, the switchable filter includes at least two first optical elements, wherein a birefringent retardation plate is optionally arranged between the at least two such first optical elements. Furthermore, the at least two first optical elements may, depending on the circumstances, have layers of different thicknesses each containing multiple light absorption transition dipole moments, but this is not mandatory.

[0027] The present invention also includes a lighting device for a screen employing the first technical solution, the screen being operable in at least two operating modes B1 (for free viewing mode) and B2 (for restricted viewing mode), wherein in restricted viewing mode, light is emitted to a viewing angle that is more limited for the observer compared to free viewing mode, and the lighting device includes: A planar, extended backlight that emits light, and optionally constructed in a direct light-emitting manner (e.g., via a locally dimmable LED matrix), and The switchable filter of the present invention is arranged in front of the backlight along the observation direction as described above.

[0028] As a supplementary solution, the present invention also includes a screen employing the first technical solution, which can operate in at least two operating modes B1 (for free viewing mode) and B2 (for restricted viewing mode). In the restricted viewing mode, light is emitted to a viewing angle that is more limited for the observer compared to the free viewing mode. The screen includes: The aforementioned lighting device, Furthermore, if the switchable filter of the lighting device does not include a first linear polarizing filter, a second linear polarizing filter P is included, arranged in front of the backlight along the viewing direction, thereby limiting the propagation direction of light emitted from the backlight and passing through the second linear polarizing filter P. A transmissive image reproduction device is arranged in front of the switchable filter along the observation direction. In the operation mode B2, a second electric field EF2 is applied, and in the operation mode B1, a first electric field EF1 is applied.

[0029] Preferably, the first linear polarizing filter or the second linear polarizing filter P is arranged in or is part of the transmissive image reproduction device.

[0030] The invention also includes a screen employing a second technical solution, which can operate in at least two working modes B1 (for free viewing mode) and B2 (for restricted viewing mode). In the restricted viewing mode, light is emitted to a viewing angle that is more limited for the observer compared to the free viewing mode. The screen includes: Image reproduction apparatus, wherein, in this principle, any type of image reproduction apparatus is taken into account, such as LC panels, OLEDs, microLEDs, and other image reproduction apparatuses. The switchable filter of the present invention, as described above, is located in front of the image reproduction device along the observation direction. In the operation mode B2, a second electric field EF2 is applied, and in the operation mode B1, a first electric field EF1 is applied.

[0031] Optionally, the switchable filter can then be reversibly installed by the user on the image reproduction device. In this case, the filter can be sold as a so-called "aftermarket product".

[0032] In the case of the aforementioned screens, when used in passenger vehicles, it is advantageous to arrange a second optical element in front of the transmissive image reproduction device along the viewing direction. This optical element includes: Multiple light absorption transition dipole moments; here, the dye mass density is greater than 1% or even greater than 10%.

[0033] In this configuration, most transition dipole moments, at least in the first state, are oriented or vary about a second preferred direction, which is optional for the second optical element, with a tolerance of at most 20° (or alternatively 10°). This second preferred direction is arranged at a predetermined angle α1 to the central normal of the second optical element (e.g., α1 = 0°, α1 = ±2°, or a value (α1) > 2° may be used). The angle α1 is measured in an optional second plane containing the aforementioned central normal; the second plane is preferably perpendicular to the first plane of the first optical element. This allows light incident on the second optical element to be transmitted or at least partially absorbed depending on its incident direction relative to the second optical element and its polarization state.

[0034] The technical solution described last advantageously ensures reduced vertical transmission, thereby reducing or completely eliminating the reflection of the images displayed on the aforementioned screen in the vehicle onto the windshield.

[0035] Within the scope of this invention, and particularly with regard to operating mode B2, a "limited angular range" means that at least 80% or 90% of the corresponding luminous density is concentrated within the defined angular range, while residual light may exist outside the defined limited angular range, typically due to technical reasons. Ideally, this residual light is minimized and decreases as the angle increases. To achieve a very high level of minimization, appropriate filters are used in addition to backlights that emit light within the limited angular range. This approach also applies to the variants described below with light guides that emit or output most of the coupled light within the limited angular range. Unlike the technical solutions of this invention, the luminous density curve of a backlight in a particularly horizontal (and possibly vertical) angular range is typically bell-shaped, but true luminous density concentration may not necessarily exist in smaller angular ranges.

[0036] Advantageously, the transition dipole moment of the first optical element (or, if applicable, a second optical element or other optical element) is constructed as one or more dichroic dyes, which are mixed with the liquid crystal in a guest-host configuration, wherein the dye mass density is typically greater than 1% or greater than 10%. For permanent transition dipole moments, the liquid crystal is preferably fixed by a curing process.

[0037] In contrast, the transition dipole moment can also be non-fixedly embedded in the liquid crystal layer as a guest-subject arrangement, so as to change the orientation and / or value of the transition dipole moment between a first state and at least one second state according to the influence of the liquid crystal layer.

[0038] Dichroic dye molecules are typically oriented parallel to liquid crystal molecules.

[0039] As an alternative, the first optical element can be constructed as a laminate of layers of a polymer thin-film polarizer.

[0040] Furthermore, the aforementioned technical solution ensures that the first optical element is non-periodic in its structure. This is advantageous because, combined with the pixel structure of the screen, there is no risk of artifacts such as the Moa interference effect.

[0041] The first preferred direction may, for example, form an angle of 0° to 45° with the surface normal of the first optical element. Furthermore, the first preferred direction may also vary within a range of the surface of the first optical element. For the purposes of this invention, an average-weighted preferred direction is applicable.

[0042] A transition dipole moment (also called a transition matrix element) is a quantum mechanical vector associated with a specific transition between the initial state (usually the ground state) and the final state (usually the excited state) of a system, such as an atom, molecule, or solid, and corresponds to the electric dipole moment associated with this transition. The direction of this vector defines the polarization of the transition, which in turn determines how the system interacts with electromagnetic waves of a specific polarization; for example, during a transition from the ground state to an excited state, light of a corresponding polarization is absorbed. The value of this vector corresponds to the strength of the interaction or the transition probability.

[0043] In this case, the first (second) preferred direction is equivalent to the orientation of the transition dipole moment of the first (second) optical element in a predetermined light propagation direction, under which the absorption is the same for any polarization of light.

[0044] The first and second preferred directions can be the same or differ by only a few degrees (maximum 10°) in orientation, and both can be perpendicular to the relevant optical element. This is the preferred case. However, depending on the specific application, the first and second preferred directions can differ by more than 10°.

[0045] Furthermore, the filter may include a polarizing filter, positioned upstream or downstream of the first or second optical element when viewed along the incident direction. Alternatively or supplementary, a λ / 4 layer may be used, for example, where circularly polarized light is converted into (substantially) linearly polarized light upon incident light.

[0046] A first exemplary manufacturing variant of manufacturing a first or second optical element using the object-subject principle is based on a dichroic dye or a mixture of dichroic dyes with a liquid crystal mixture or compound, and includes the following manufacturing steps (US 9,481,658 B2 or WO2021 / 177308A1, paragraph 37 and below): A thin film is applied to a substrate with low or no birefringence, defining the orientation of molecules relative to the surface, typically parallel or perpendicular to it. Polymers are used for this purpose, preferably polyvinyl alcohol or polyimide.

[0047] Alternatively, the surfaces may be optically or mechanically treated to improve the subsequent quality of molecular orientation.

[0048] A mixture of dichroic dye and thermotropic liquid crystal compound or polymer is applied.

[0049] The penetration of light causes the side chains to partially condense, thereby permanently orienting the fuel perpendicular to the surface.

[0050] An alternative second manufacturing variant employs a thermotropic liquid crystal dichroic dye (see JP2011-237513A) and includes the following steps: Prepare the corresponding dyes and add polar groups.

[0051] Apply the dye mixture and then photo-orient and cure the dye mixture using polarized light.

[0052] Regarding different manufacturing variations, for example, the following materials should be taken into account, although this list is not exhaustive: As a polymer substrate with low or no birefringence: TAC is preferred. As dichroic substances or mixtures: dichroic dyes (preferably azo dyes) or dichroic metal nanoparticles (preferably gold, silver, copper, and aluminum); they are generally a single dye or usually a mixture of up to three different dyes to achieve absorption across the entire spectrum. For surface treatment via the orientation of dyes or liquid crystal materials: polymers, preferably polyvinyl alcohol or polyimide, For the purposes of thermotropic liquid crystal compounds or polymers, see JP 2011-237513A.

[0053] Chemical groups used for crosslinking with thermotropic liquid crystal compounds or polymers include: m-acryloyl, epoxy, oxetyl, and styryl, with methacryloyl being preferred. Alternatively, polymerizable liquid crystal compounds may be used, for example, those described in JP6268730B2.

[0054] Polymerizable liquid crystal dichroic dyes, such as azo dyes.

[0055] The at least one dye consists of dye molecules, wherein a transition dipole or transition dipole moment is advantageously associated with each dye molecule, i.e., each dye molecule corresponds to one transition dipole or transition dipole moment. The mass fraction of the dye in the material of the corresponding layer of the relevant optical element is typically at least 0.01%, preferably 1% to 15%. In special cases, for liquid crystal dichroic dyes, the concentration can even reach 95%. The dyes or dye mixtures used for different layers within the optical element may vary, but are not required to do so.

[0056] The aforementioned filters, lighting devices, or screens are advantageously used in mobile devices, motor vehicles, aircraft or ships, payment terminals, or access control systems. In this case, switching between the aforementioned operating modes can be performed to protect sensitive data, i.e., presented in a manner perceptible to only one observer, or alternatively, the image content can be presented to multiple observers simultaneously.

[0057] In principle, if the above parameters change within certain limits, the performance of the present invention can still be maintained.

[0058] Of course, within the scope of this invention, the features described above and below can be combined not only in the manner given in this application, but also in other ways or applied individually. Attached Figure Description

[0059] The invention will now be described in detail with reference to the accompanying drawings, which reveal the essential features of the invention, and in conjunction with embodiments. These embodiments are for illustrative purposes only and do not constitute limitation. For example, the description of an embodiment comprising multiple components or components does not imply that all of these elements or components are indispensable. Rather, other embodiments may include alternative elements and components, reduced elements or components, or additional elements or components. Unless otherwise stated, elements or components of different embodiments may be combined with each other. Changes and variations described in one embodiment may also be applied to other embodiments. To avoid repetition, the same or corresponding components in different drawings are represented by the same symbols and will not be described again.

[0060] Figure 1 This is a schematic diagram of a switchable filter.

[0061] Figure 2 Examples of transmittance for two parameter sets ID1 and ID2.

[0062] Figure 3 Examples of transmittance for two parameter sets, ID3 and ID4.

[0063] Figure 4 Examples of transmittance for two parameter sets, ID5 and ID6.

[0064] Figure 5This is a schematic diagram of another switchable filter.

[0065] Figure 6 This is a schematic diagram of an illumination device with a switchable filter.

[0066] Figure 7 This is a schematic diagram of a first screen with a switchable filter.

[0067] Figure 8 This is a schematic diagram of a second screen with a switchable filter. Detailed Implementation

[0068] The diagram is not drawn to scale and is only a schematic diagram.

[0069] Figure 1 A schematic diagram of the switchable filter 5 is shown, including: First optical element 1, comprising: A large number of light-absorbing transition dipole moments are arranged in a single layer with a thickness of at least 0.1 μm and a maximum of 40 μm, or in multiple separate layers with a total thickness of up to 40 μm (which may exist, depending on the case, in the adhesive layer between individual transition dipole moment layers or substrate layers, not included here). Figure 1 In the first optical element, a few transition dipole moments are schematically shown with arrows, but in reality, there are a large number of transition dipole moments. The aforementioned transition dipole moment is achieved using at least two (different) dichroic dyes. Among all transition dipole moments, the transition dipole moments with a relative proportion p (0.6 ≤ p ≤ 1.0, typically p < 1) (in this example) are permanently oriented parallel to or vary around a first preferred direction selectable for the first optical element 1 with a tolerance of up to 15°. Figure 1 The diagram shows three arrows, representing three transition dipole moments as examples and representations of relative proportions. Of the 14 transition dipole moments shown, 12 satisfy the aforementioned orientation criteria, i.e., the inequality 0.6 ≤ p ≤ 1.0 is also satisfied here. This first preferred orientation is arranged at a predetermined angle α (e.g., α = 0°, α = ±2°, or a value (α) > 2°) with respect to the central normal of the first optical element 1 (see the dotted line). The angle α is measured within an optional first plane containing the aforementioned central normal, and this first plane is preferably parallel to the edge of the first optical element 1, such as the lower edge. This allows light incident on the first optical element 1 in the incident direction and polarization state to be transmitted or at least partially absorbed according to its incident direction and polarization state relative to the first optical element 1. (Not shown in the figure) A device for optionally generating a first electric field EF1 or a second electric field EF2. A liquid crystal layer 3 is arranged behind or in front of the first optical element 1 along the observation direction. A first electric field EF1 or a second electric field EF2 acts on the liquid crystal layer and thereby affects the polarization state of light passing through the liquid crystal layer, wherein the absolute values ​​of the first electric field EF1 and the second electric field EF2 differ by at least 0.1 MV / m. The transmission characteristics of the switchable filter 5 differ between a first operating mode B1 where the first electric field EF1 is applied and a second operating mode B2 where the second electric field EF2 is applied, wherein, except for optional tolerances, at at least one point on the switchable filter 5 (preferably at at least five points, more preferably distributed across multiple points on the entire surface of the switchable filter 5), the corresponding relative transmittances under operating modes B1 and B2 are respectively obtained through a first transmittance T for the first operating mode B1. B1 (β) and the second transmittance T for the second operating mode B2 B2 (β) is used to describe the transmittance, which is related to the angle β and is normalized so that the transmittance value at a predetermined angle β=α is applicable to T. B1 (α) = 1 and T B2 (α) = 1, Therefore, linearly polarized light or elliptically polarized light with a major-to-minor axis ratio of at least 4:1 is: If the switchable filter 5 is incident at an angle (β) of α-5°≤β≤α+5°, then T B1 (β) / T B2 The ratio of (β) is greater than 0.9 + log 10 (p) and less than 1.3 - log 10 (p) If the switchable filter 5 is incident at an angle (β) of α-30°≤β≤α-20° or α+20°≤β≤α+30°, then T B1 (β) / T B2 The ratio of (β) is greater than 2 • (1 + log) 10 (p)), and If the switchable filter 5 is incident at an angle (β) of α-45°≤β≤α-35° or α+35°≤β≤α+45°, then T B1 (β) / T B2 The ratio of (β) is greater than 9 • (1 + 2 • log) 10 (p)).

[0070] In principle, the following should apply: within the angular range of β≤α-5° or α+5°≤β, the first transmittance T used for the first operating mode. B1 (β) is typically greater than the second transmittance T used in the second operating mode B2. B2(β). As described below, this is primarily achieved by selecting the first electric field EF1 and the second electric field EF2. The following implementation scheme should apply: linearly polarized or elliptically polarized light with a major-to-minor axis ratio of at least 4:1 is incident on the switchable filter 5, and its polarization is mostly parallel to the aforementioned first plane, with a maximum tolerance of 5°. For convenience, α = 0° should be applied for all subsequent observations.

[0071] Depending on the specific design of the liquid crystal layer 3, such as TN (Twisted Nematic), VA (Vertical Alignment), IPS (In-Plane Switching), FFS (Fringe Field Switching), or other possible types, if the liquid crystal layer 3 is arranged behind the first optical element 1 in the viewing direction, the first electric field EF1 is selected such that, after passing through the liquid crystal layer 3, the transmitted light has at least 40% of its electric field component perpendicular to the first plane, wherein its polarization is mostly perpendicular to the first plane (or at an optional angle in the range of 45° to 135°), with a maximum tolerance of 5°. The second electric field EF2 is selected such that, after passing through the liquid crystal layer 3, the transmitted light has at least 80%, preferably more than 85%, of its electric field component parallel to the first plane. Under the above premise, that is, the polarization of the incident light is mostly parallel to the aforementioned first plane, with a maximum tolerance of 5°, the field strength of the second electric field EF2 is, for example, 0 V / m, i.e., substantially zero electric field. The field strength of the first electric field EF1 can exceed 0.1 MV / m. This electric field is preferably an alternating field, changing its polarity in a rectangular or sinusoidal manner at a frequency on the order of 50, preferably at least 0.8 kHz, for example at at least 1.0 kHz. Frequencies higher than 1.0 kHz can also be used. In other words, in the second operating mode B2 with the second electric field EF2, a polarization state as pure as possible is generated because, after passing through the liquid crystal layer 3, the transmitted light has at least 80% of its electric field component parallel to the first plane. In contrast, in the first operating mode B1 with the first electric field EF1, the electric field component is mainly mixed or significantly rotated because, after passing through the liquid crystal layer 3, the transmitted light has at least 40% of its electric field component perpendicular to the first plane. This is achieved, for example, when the liquid crystal layer 3 is in the form of an IPS cell or when circular polarization is used after the liquid crystal layer 3.

[0072] The essence of this invention lies in the fact that the selection of the transition dipole moment with a relative proportion p among all transition dipole moments, combined with the different selections of a first electric field EF1 and a second electric field EF2 with an absolute value difference of at least 0.1 MV / m and the resulting polarization effect, can satisfy the above-mentioned inequality. This inequality provides the aforementioned angle-dependent comparison of transmittance or the aforementioned ratio. Therefore, Figure 2Exemplary transmittance for two parameter sets, ID1 and ID2, is shown exemplarily. This is a simulation based on measurements. The parameters used here are for light with a wavelength of 500 nm and a refractive index with a real part of 1.5. For ID1, the layer thickness of the dichroic dye is specified as 6 μm, the imaginary part of the refractive index for p-polarized light is 0.15, and the imaginary part of the refractive index for s-polarized light is 0.0025. In ID2, the layer thickness is specified as 6 μm, the imaginary part of the refractive index for p-polarized light is 0.15, and the imaginary part of the refractive index for s-polarized light is 0.005. Furthermore, the second electric field EF2 is zero, while the absolute value of the first electric field EF1 is 0.1 MV / m. It can be seen that in the case of ID2, T... B1 (β) / T B2 The ratio of (β) differs significantly from the ratio of ID1 mentioned earlier, especially from angles where β < -40° or β > 40°, because the absorption of s-polarized light in ID1 is reduced compared to ID2. However, both parameter sets ID1 and ID2 satisfy the inequality derived in this invention. Parameter sets ID1 and ID2 even satisfy the following condition: linearly polarized light or elliptically polarized light with a major semi-axis to minor semi-axis ratio of at least 4:1 is: If the light is incident on the switchable filter (5) at an angle (β) of α-5°≤β≤α+5°, then T B1 (β) / T B2 The ratio of (β) is greater than 1.0 + log 10 (p) and less than 1.3 - log 10 (p) If the light is incident on the switchable filter (5) at an angle (β) of α-30°≤β≤α-20° or α+20°≤β≤α+30°, then T B1 (β) / T B2 The ratio of (β) is greater than 3 • (1 + log) 10 (p)), and If the light is incident on the switchable filter (5) at an angle (β) of α-45°≤β≤α-35° or α+35°≤β≤α+45°, then T B1 (β) / T B2 The ratio of (β) is greater than 16 • (1 + 2 • log) 10 (p)).

[0073] One important aspect of the device's effectiveness lies in the fact that, by switching between a first operating mode B1 (where a first electric field EF1 is applied) and a second operating mode B2 (where a second electric field EF2 is applied, and the absolute values ​​of the first and second electric fields EF1 and EF2 differ by at least 0.1 MV / m), according to a specific technical solution, only in one operating mode (such as the first operating mode B1) is the p-polarized light incident on the liquid crystal layer substantially converted into s-polarized light, which then enters the first optical element 1 and is also transmitted at an angle greater than 20°. In contrast, according to a specific technical solution, only in another operating mode (such as the second operating mode B2) is the s-polarized light incident on the liquid crystal layer 3 substantially converted into p-polarized light, which then enters the first optical element 1 and is also absorbed at an angle greater than 20°. Ultimately, the aforementioned transmittance T... B1 (β) / T B2 (β) holds true within the given angular range.

[0074] If the transition dipole moment for absorption is also composed of at least two dichroic dyes, wherein the dye mass density is typically greater than 1%, it will help satisfy the inequality for the given reasonable transmittance.

[0075] Normalized T for transmittance B1 (α) = 1 and T B2 (α) = 1, and the following should be noted: Of course, angles β and α are measured in the same plane mentioned above. In principle, T B1 (α) > 1 and / or T B2 (α) > 1 also applies to angle β ≠ α. In many cases, T B1 (α) < 1 and / or T B2 (α) < 1 also applies to angle β ≠ α.

[0076] also, Figure 3 Exemplary transmittance values ​​for two parameter sets, ID3 and ID4, are shown illustratively. Figure 4 Exemplary transmittance values ​​for two parameter sets, ID5 and ID6, are shown. In the cases of ID3-ID6, light with a wavelength of 500 nm is incident, and the dye layer thickness is 6 μm. The refractive index of p-polarized light is 1.5 + 0.15i, and the refractive index of p-polarized light is 1.5 + 0.0025i. Absorption occurs for positive complex refractive indices. In the case of ID3, the linear polarization of light differs by 45° between B1 and B2, and by 60° in the case of ID4. For ID5, the light is linearly polarized in state B2 and circularly polarized in state B2. For ID6, when light strikes optical element 1, the light is linearly polarized in state B2 and elliptically polarized in state B2.

[0077] In a preferred embodiment, when a second electric field EF2 is applied, light penetrating the liquid crystal layer 3 is transmitted substantially unchanged, while when a first electric field EF1 is applied, the incident light undergoes circular or ellipsoidal polarization, or its polarization is rotated by 90°. In essence, this indicates that at the interface, the orientation of the liquid crystal molecules is determined by the electric field and surface induction forces; therefore, the liquid crystal molecules are not ideally oriented, resulting in a slight, undesirable change in polarization.

[0078] If the liquid crystal layer 3 is arranged behind the first optical element 1 along the observation direction, linearly polarized light or elliptically polarized light is preferably incident, wherein the ratio of the major semi-axis to the minor semi-axis is at least 4:1 (preferably at least 5:1 or greater). This can be achieved, for example, by a linear polarizing filter in the optical path, or by a λ / 4 layer in the case of circularly polarized light.

[0079] also, Figure 5 A schematic diagram of another switchable filter 5 is shown. Wherein, if the liquid crystal layer 3 is arranged in front of the first optical element 1 along the observation direction, that is, a polarizing filter X is typically also provided in front of the liquid crystal layer 3 along the observation direction, then... Figure 1 The values ​​of the first electric field EF1 and the second electric field EF2 described herein can also be used to generate operating modes B1 and B2. This structure is typically used in conjunction with a backlit transparent image reproduction device, in which a switchable filter 5 is positioned. In this technical solution, at least 75%, or even 90%, of the light transmitted by the first optical element 1 is substantially s-polarized at an angle greater than 20°. Thus, depending on the specific operating mode, p-polarized or s-polarized light is generated relative to the first plane (at least 95%), which is then largely absorbed or transmitted at an angle greater than 20°, depending on the specific orientation of the polarizing filter X, which may be part of the aforementioned image reproduction device.

[0080] In another technical solution, the switchable filter 5 includes at least two first optical elements, wherein a birefringent retardation plate is optionally arranged between the at least two such first optical elements. Furthermore, the at least two first optical elements may, depending on the circumstances, have layers of different thicknesses, each containing multiple light absorption transition dipole moments, but this is not mandatory.

[0081] Figure 6 A schematic diagram of an illumination device for a screen with a switchable filter 5, employing a first technical solution, is shown. The screen can operate in at least two operating modes, B1 (for free viewing mode) and B2 (for restricted viewing mode). In restricted viewing mode, light is emitted to a viewing angle that is more limited for the observer compared to free viewing mode. The illumination device includes: A planar extended backlight 8, which is luminous and can optionally be constructed in a direct luminous manner (e.g., through a locally dimmable LED matrix), and The switchable filter 5 of the present invention is arranged in front of the backlight 8 along the observation direction as described above.

[0082] also, Figure 7 A schematic diagram of a first screen with a switchable filter 5, employing a first technical solution, is shown. This screen can operate in at least two operating modes, B1 (for free viewing mode) and B2 (for restricted viewing mode). In restricted viewing mode, light is emitted to a viewing angle that is more limited for the observer compared to free viewing mode. The screen includes: The aforementioned lighting device, Furthermore, if the switchable filter 5 of the lighting device does not contain a first linear polarizing filter, a second linear polarizing filter P is included, arranged in front of the backlight 8 along the viewing direction, thereby limiting the propagation direction of light emitted from the backlight 8 and passing through the second linear polarizing filter P. A transmissive image reproduction device 11 is arranged in front of the switchable filter 5 along the observation direction. In the operation mode B2, a second electric field EF2 is applied, and in the operation mode B1, a first electric field EF1 is applied.

[0083] Preferably, the first linear polarizing filter or the second linear polarizing filter P is arranged in or is part of the transmissive image reproduction device 11.

[0084] also, Figure 8 A schematic diagram of a second screen with a switchable filter 5, employing a second technical solution, is shown. This screen can operate in at least two operating modes, B1 (for free viewing mode) and B2 (for restricted viewing mode). In restricted viewing mode, light is emitted to a viewing angle that is more limited for the observer compared to free viewing mode. The screen includes: Image reproduction device 12, wherein, in this principle, any type of image reproduction device 12 is considered, such as LC panel, OLED, microLED and other image reproduction devices. The switchable filter 5 of the present invention, located in front of the image reproduction device 12 along the observation direction as described above, In the operation mode B2, a second electric field EF2 is applied, and in the operation mode B1, a first electric field EF1 is applied.

[0085] Optionally, the switchable filter 5 can then be reversibly installed on the image reproduction device 12 by the user. In this case, the filter 5 can be sold as a so-called "aftermarket product".

[0086] Within the scope of this invention, and particularly with respect to operating mode B2, "limited angular range" means that at least 80% or 90% of the corresponding luminous density is concentrated within the defined angular range, while residual light may exist outside the defined limited angular range, which is usually caused by technical reasons. Ideally, this residual light is minimized and decreases as the angle increases.

[0087] Furthermore, the switchable filter 5 may include a polarizing filter, which is positioned upstream or downstream of the first optical element 1 when viewed along the incident direction. As an alternative or supplementary solution, a λ / 4 layer may also be used, for example, when circularly polarized light is incident, the circularly polarized light is converted into (substantially) linearly polarized light based on this layer.

[0088] The solution of the present invention to achieve the above-mentioned objective lies in describing a filter having optical elements, wherein light incident on the optical elements is transmitted or partially or completely absorbed according to its incident direction and polarization characteristics—(not primarily) according to its position. With this filter, the transmission of light is affected angularly—optionally perpendicularly relative to a seated or standing observer—and switching between at least two operating modes is possible. Specifically, the angular correlation ratio of the transmission behavior between specific directions is defined. Furthermore, the filter can also be used in conjunction with self-emissive screens (such as OLEDs).

[0089] The invention described above can be advantageously combined with image playback devices and is widely used in places where confidential information needs to be displayed and / or entered, such as entering a PIN code or displaying data on an ATM or payment terminal, or entering a password, or reading emails on a mobile device. As mentioned above, the invention can also be used in passenger vehicles to selectively block interfering image content for the driver or passengers.

[0090] Explanation of reference numerals in the attached figures 1: First optical element 2: Second optical element 3: Liquid crystal layer 5: Switchable filter 8: Backlight 11: Transmissive Image Reproduction Device 12: Image Reproduction Device P, X: Polarizing filters

Claims

1. A switchable filter (5), comprising: The first optical element (1) includes: Multiple optical absorption transition dipole moments are arranged in a single layer of at least 0.1 μm and at most 40 μm, or in multiple separate layers with a total thickness of at most 40 μm. In this context, the transition dipole moments of relative proportion p among all transition dipole moments are permanently or at least in the first state oriented or vary about a first preferred direction selectable for the first optical element (1) with a tolerance of up to 15°, wherein 0.6 ≤ p ≤ 1.0, and the first preferred direction is arranged at a predetermined angle α with respect to the central normal of the first optical element (1), wherein the angle α is measured in an optional first plane containing the central normal. This allows light incident on the first optical element (1) in the incident direction and polarization state to be transmitted or at least partially absorbed according to its incident direction and polarization state relative to the first optical element (1). A device for selectively generating a first electric field (EF1) or a second electric field (EF2), A liquid crystal layer (3) is arranged behind or in front of the first optical element (1) along the observation direction. A first electric field (EF1) or a second electric field (EF2) acts on the liquid crystal layer and thereby affects the polarization state of light penetrating the liquid crystal layer. The absolute values ​​of the first electric field (EF1) and the second electric field (EF2) differ by at least 0.1 MV / m. If the liquid crystal layer (3) is arranged in front of the first optical element (1) along the observation direction, then the first linear polarizing filter is located in front of the liquid crystal layer (3) along the observation direction. This causes the transmission characteristics of the switchable filter (5) to differ between a first operating mode B1 with the first electric field (EF1) applied and a second operating mode B2 with the second electric field (EF2) applied, wherein, except for optional tolerances, at at least one point on the switchable filter (5), the corresponding relative transmittances under the two operating modes B1 and B2 are respectively obtained through a first transmittance T for the first operating mode B1. B1 (β) and the second transmittance T for the second operating mode B2 B2 (β) describes the transmittance, which is related to angle β and is normalized such that the transmittance value at a predetermined angle β=α is applicable to T. B1 (α) = 1 and T B2 (α) = 1, Therefore, linearly polarized light or elliptically polarized light with a major-to-minor axis ratio of at least 4:1 is: If the switchable filter (5) is incident at an angle (β) of α-5°≤β≤α+5°, then T B1 (β) / T B2 The ratio of (β) is greater than 0.9 + log 10 (p) and less than 1.3 - log 10 (p) If the switchable filter (5) is incident at an angle (β) of α-30°≤β≤α-20° or α+20°≤β≤α+30°, then T B1 (β) / T B2 The ratio of (β) is greater than 2·(1+ log) 10 (p)), and If the switchable filter (5) is incident at an angle (β) of α-45°≤β≤α-35° or α+35°≤β≤α+45°, then T B1 (β) / T B2 The ratio of (β) is greater than 9 · (1 + 2 · log 10 (p)).

2. The switchable filter (5) according to claim 1, wherein, The first optical element (1) includes a plurality of light absorption transition dipole moments, which are arranged in a single layer with a thickness of at least 1 μm and a maximum of 40 μm, or arranged in a plurality of separate layers with a total thickness of at most 40 μm. Therefore, linearly polarized light or elliptically polarized light with a major-to-minor axis ratio of at least 4:1 is: If the switchable filter (5) is incident at an angle (β) of α-5°≤β≤α+5°, then T B1 (β) / T B2 The ratio of (β) is greater than 1.0 + log 10 (p) and less than 1.3 - log 10 (p) If the switchable filter (5) is incident at an angle (β) of α-30°≤β≤α-20° or α+20°≤β≤α+30°, then T B1 (β) / T B2 The ratio of (β) is greater than 3·(1+ log) 10 (p)), and If the switchable filter (5) is incident at an angle (β) of α-45°≤β≤α-35° or α+35°≤β≤α+45°, then T B1 (β) / T B2 The ratio of (β) is greater than 16 · (1 + 2 · log 10 (p)).

3. The switchable filter (5) according to claim 1 or 2, wherein, The first optical element (1) and / or the liquid crystal layer (3) and / or the means for selectively generating the first electric field EF1 or the second electric field EF2 are divided into multiple individually switchable segments so that local switching can be performed between the corresponding possible operating modes.

4. A lighting device for a screen, the screen being operable in at least a first operating mode B1 for a free viewing mode and a second operating mode B2 for a restricted viewing mode, wherein light is emitted into a viewing angle that is more limited for the observer than in the free viewing mode, the lighting device comprising: A planar extended backlight (8), which emits light, and The switchable filter (5) according to any one of claims 1 to 3 is arranged in front of the backlight (8) along the observation direction.

5. A screen operable in at least a first operating mode B1 for a free viewing mode and a second operating mode B2 for a restricted viewing mode, wherein light is emitted into a viewing angle that is more limited for an observer than in the free viewing mode, the screen comprising: The lighting device according to claim 4, If the first linear polarizing filter (X) is not arranged in the switchable filter (5) of the illumination device, the second linear polarizing filter (P) is arranged in front of the backlight (8) along the observation direction, thereby limiting the propagation direction of light emitted from the backlight and passing through the second linear polarizing filter (P), and A transmissive image reproduction device (11) is arranged in front of the switchable filter (5) along the observation direction. The second electric field (EF2) is applied in the second operating mode B2, and the first electric field (EF1) is applied in the first operating mode B1.

6. The screen according to claim 5, wherein, If the first linear polarizing filter (X) is present, then the first linear polarizing filter (X) is arranged in or is part of the transmissive image reproduction device (11); otherwise, the second linear polarizing filter (P) is arranged in or is part of the transmissive image reproduction device (11).

7. A screen operable in at least a first operating mode B1 for a free viewing mode and a second operating mode B2 for a restricted viewing mode, wherein light is emitted into a viewing angle that is more limited for an observer than in the free viewing mode, the screen comprising: Image reproduction device (12). The switchable filter (5) according to any one of claims 1 to 3 is arranged in front of the image reproduction device (12) along the observation direction. The second electric field (EF2) is applied in the second operating mode B2, and the first electric field (EF1) is applied in the first operating mode B1.

8. The screen according to claim 7, wherein, The switchable filter (5) is then installed by the user and / or reversibly on the image reproduction device (12).

9. The screen according to any one of claims 7 to 8, wherein, A second optical element (2) is arranged in front of the image reproduction device (12) along the observation direction, the optical element comprising: Multiple optical absorption transition dipole moments, In this context, most of the transition dipole moments are permanently or at least in the first state oriented or fluctuate around a second preferred direction, which is optional for the second optical element (2), with a tolerance of up to 20°. This second preferred direction is arranged at a predetermined angle α1 to the central normal of the second optical element (2), and the angle α1 is measured in an optional second plane containing the central normal. This causes light incident on the second optical element (2) to be transmitted or at least partially absorbed according to its incident direction relative to the second optical element (2) and its polarization state.

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