Optical element, switchable optical filter, lighting device and screen

Abstract

The invention relates to a first optical element (1) comprising a plurality of light absorption transition dipole moments. The majority of the transition dipole moments are permanently or at least in a first state, oriented parallel to or varied about a first preferred direction selectable for the first optical element (1) with a tolerance [tau] of [tau] < = 20 DEG, the transition dipole moments oriented parallel to the first preferred direction with the tolerance [tau] having a density N1, the remaining transition dipole moments have a density N2 such that light entering the first optical element (1) is transmitted or at least partially absorbed depending on its direction of incidence with respect to the first optical element (1) and its polarization state. According to the invention, an inequality (I) is satisfied on the optical element (1) permanently or at least in the above-mentioned first state for the respective ratio of densities N1 to N2, such that a larger tolerance value [tau] is at least partially compensated with the respective increasing ratio of densities N1 to N2 of transition dipole moments, whereby the absorption of p-polarized light incident on the optical element (1) at an angle greater than 45 DEG is enhanced. The invention further discloses a first switchable optical filter (5), a second switchable optical filter (5a), a lighting device and a screen.

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] In WO 2012 / 033583 A1, switching between free and restricted viewing angles is achieved by controlling the liquid crystals between the so-called "color-emitting" layers. This process results in light loss and is technically quite challenging.

[0007] US 2012 / 0235891 A1 describes an extremely complex screen backlight. According to this case... Figure 1 and Figure 15 It not only uses multiple light guides but also other complex optical components, such as microlens assembly 40 and prism structure 50, which shape the light originating from the rear illumination along the path to forward illumination. Its implementation is costly, technically challenging, and also results in light loss. According to US 2012 / 0235891 A1... Figure 17 In the variant shown, both light sources 4R and 18 produce light with narrow illumination angles, where the light from the rear light source 18 is transformed into light with a wide illumination angle after a complex process. As previously mentioned, such a complex transformation significantly reduces brightness.

[0008] 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.

[0009] 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 of operating modes. However, the polymer scattering particles selected in this application 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.

[0010] 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. Summary of the Invention

[0011] Therefore, the object of the present invention is to describe an optical element in which light incident upon the optical element is transmitted or partially or completely absorbed according to its incident direction and polarization characteristics—(not primarily) according to its position. Optical effects are needed to address production-related orientation tolerances. By using a switchable filter for the optical element, the transmission of light can be affected angularly—optionally relative to a seated or standing viewer—where switching between at least two operating states is possible. In this case, the transmission behavior should particularly be able to be switched for certain directions. Furthermore, the present invention also discloses illumination devices and screens using switchable filters.

[0012] The solution of the present invention to achieve the above objective is a first optical element, comprising: Multiple optical absorption transition dipole moments, where the corresponding absorption cross section is represented by σ. abs This indicates and can be selectively applied to one wavelength, multiple selected wavelengths, or, as is commonly the case, multiple wavelengths in the human visible spectrum. In this configuration, most transition dipole moments are permanently or at least in the first state oriented parallel to or varying around a first preferred direction selectable for the first optical element with a tolerance τ ≤ 19°, preferably τ ≤ 15° (the tolerance τ applies to both directions, i.e., ±τ is added to the value of the corresponding angle). The first preferred direction is arranged at an angle α relative to the central normal of the first optical element, wherein this angle α is measured in an optional first plane containing the aforementioned central normal. The transition dipole moments oriented parallel to the first preferred direction with tolerance τ have a density N1, and the remaining transition dipole moments (i.e., those outside the aforementioned tolerance range) have a density N2. This causes light incident on the first optical element to be transmitted or at least partially absorbed depending on its incident direction relative to the first optical element and its polarization state. Wherein, on the optical element, the ratio of the corresponding densities N1 and N2 for the transition dipole moment permanently or at least in the first state described above satisfies the inequality. This allows for at least partial compensation of the larger tolerance value τ by utilizing the ratio of the correspondingly increased transition dipole moment density N1 to N2, thereby enhancing the absorption of p-polarized light incident on the optical element at an angle greater than 45° in the first plane.

[0013] Multiple optical absorption transition dipole moments are arranged in a layer at least 0.2 micrometers thick. Multiple elements, such as those formed by OCA (Optical Calibration Amplification), may also be present. Optically Clear Adhesive The first optical element 1 comprises two transition dipole moment layers separated by an optically transparent adhesive (OCA) and / or a substrate. The thickness of the transition dipole moment layer can be, for example, from 0.2 μm to 50 μm, preferably from 0.2 μm to 20 μm, and more preferably from 1 μm to 10 μm. In a preferred embodiment, the first optical element 1 comprises two transition dipole moment layers with thicknesses of 1 μm to 10 μm, each layer having a substrate (e.g., made of TAC or other non-birefringent or slightly birefringent material with a thickness preferably less than 100 μm), wherein the two substrates are further separated by an OCA layer. (Optically Clear Adhesive) They stick together.

[0014] Furthermore, this invention discloses a method for addressing manufacturing-related limitations when orienting the transition dipole moment on an optical element. Specifically, this method involves ensuring that the ratio of the corresponding densities N1 and N2 of the transition dipole moment satisfies the inequality only when the ratio is permanently or at least in this first state. The optical elements thereby utilize the ratio of the correspondingly increased transition dipole moment densities N1 and N2 to at least partially compensate for the larger manufacturing tolerance value τ.

[0015] Preferably, the ratio of the corresponding densities N1 to N2 for the transition dipole moment satisfies the inequality permanently or at least in the first state described above. .

[0016] The greater the relative proportion of the remaining transition dipole moments of density N2 (i.e., outside the above tolerance range), the worse the general transmittance of the optical element in all directions in general.

[0017] The ratio of densities N1 and N2 can be measured indirectly, for example, through DLS. (Dynamic Light Scattering) The method of dynamic light scattering is used to implement this, which is a known approach in the prior art and will not be described further herein. Following the inequalities of this invention, the first optical element suitable for the purpose of the invention can be evaluated and selected after it has been manufactured.

[0018] Another solution of the present invention to achieve the above objective is a first switchable filter, comprising: The aforementioned first optical element, A device for selectively generating a first electric field EF1 or a second electric field EF2, such as an ITO layer connected to a signal generator. A liquid crystal layer is arranged behind or in front of the 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 the light passing through the liquid crystal layer. When the liquid crystal layer is arranged in front of the first optical element along the observation direction, the first linear polarizing filter is located in front of the liquid crystal layer along the observation direction. This causes the transmission characteristics of the first switchable filter to differ between the first operating mode B1 (in which a first electric field EF1 is applied) and the second operating mode B2 (in which a second electric field EF2 is applied).

[0019] In cases where the transition dipole moment can change, for example, through a change in a so-called guest-substrate liquid crystal cell, such a guest-substrate liquid crystal cell can directly correspond to the aforementioned liquid crystal layer, but it is not necessary to do so.

[0020] 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 this respect, it substantially indicates that at this 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.

[0021] For embodiments employing TN liquid crystals, the following applies: on the large surface confining the liquid crystal layer, the orientation of the 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 within the plane is less than 45°, typically approximately 25° to 40°.

[0022] The first electric field EF1 may have a field strength not equal to 0 V / pm, on the order of 1 V / pm, for example, as a square wave of 1 kHz, while the field strength of the second electric field EF2 may be 0 V / pm. However, this embodiment can also be exactly the opposite, or both fields EF1 and EF2 may be non-zero electric fields.

[0023] If the liquid crystal layer is arranged behind the first optical element along the viewing direction, it is preferable that linearly polarized or elliptically polarized light enters the liquid crystal layer, 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 linearly polarizing filter in the optical path, or, in the case of using circularly polarized light, by a λ / 4 layer.

[0024] Advantageously, the first optical element (and, if present, each of other such optical elements) and / or the liquid crystal layer and / or the means for generating the first electric field EF1 or the second electric field EF2 are divided into multiple individually switchable segments so as to enable local switching between corresponding possible operating states.

[0025] In another embodiment, the switchable filter includes at least two first optical elements, wherein a birefringent layer is optionally disposed between the at least two such first optical elements. Furthermore, the at least two first optical elements may, depending on the situation, have layers of different thicknesses, each containing a plurality of light absorption transition dipole moments, but this is not mandatory.

[0026] Furthermore, another solution of the present invention to achieve the above-mentioned objective lies in a second switchable filter, comprising: The second optical element includes: Multiple optical absorption transition dipole moments, where the corresponding absorption cross section is represented by σ. abs This indicates and can be selectively applied to one wavelength, multiple selected wavelengths, or, as is commonly the case, multiple wavelengths in the human visible spectrum. The transition dipole moment is composed of one or more dichroic dyes, and is contained in the second liquid crystal layer in a guest-host configuration. In this configuration, most transition dipole moments are also, at least in the first state, oriented parallel to or varying around a second preferred direction selectable for the second optical element with a tolerance τ ≤ 19°, preferably τ ≤ 15° (the tolerance τ also applies to two directions, ±τ), wherein the second preferred direction is arranged at an angle α relative to the central normal of the second optical element, wherein this angle α is measured in an optional second plane containing the aforementioned central normal, and wherein the transition dipole moments oriented parallel to the second preferred direction with tolerance τ have a density N1, and the remaining transition dipole moments have a density N2. 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, its polarization state, and the state of the second liquid crystal layer at the point of light incidence. An apparatus for selectively generating at least a first electric field EF1 or a second electric field EF2, wherein the corresponding electric field acts on the second liquid crystal layer such that the transmission characteristics of the second switchable filter differ between a first operating mode B1 (where the first electric field EF1 is applied and the second liquid crystal layer is in the first state) and a second operating mode B2 (where the second electric field EF2 is applied and the second liquid crystal layer is in the second state). In the second optical element, at least in the first state described above, the ratio of the corresponding densities N1 and N2 for the transition dipole moment satisfies the inequality. This allows for at least partial compensation of the larger tolerance value τ by utilizing the ratio of the correspondingly increased transition dipole moment density N1 to N2, thereby enhancing the absorption of p-polarized light incident on the second optical element at an angle greater than 45° in the second plane.

[0027] It should be noted here that the second switchable filter is generally applicable: at least one of the first states of the plurality of transition dipole moments can actually be equivalent to the second state of the second operating state B2, which will be described in detail below. That is, specifically, the boundary conditions of the first state (which mainly involve tolerances and orientation relative to the second preferred direction) also apply to the second state.

[0028] The device for selectively generating at least a first electric field EF1 or a second electric field EF2 can be advantageously designed such that different electric fields EF1, EF2 (or, depending on the situation, different electric fields EF3, EF4, etc.) are simultaneously applied to different locations on the liquid layer. This enables position-dependent partial switching of the operating mode of the second switchable filter.

[0029] For the second switchable filter, optionally, the ratio of the corresponding densities N1 to N2 of the transition dipole moment on its second optical element satisfies an inequality different from that in the first state, at least in the second state described above (for the second operating mode B2). This reduces the absorption of p-polarized light incident on the second optical element at an angle greater than 45° in the second plane. In this way, higher transmittance is achieved along the second plane in the second state described above. In this case, when viewed along the second plane, the second operating mode B2 at least partially allows for a larger viewing angle, i.e., a free viewing mode.

[0030] Advantageously, in the first and second switchable filters, the potential difference between the electrodes used to generate the first electric field EF1 and the second electric field EF2 is at least 2 volts. Other operating modes B3, B4, etc., can also be explicitly provided, whose electric fields EF3, EF4, etc., differ from those of EF1 and EF2. Furthermore, as described above, operating modes B1, B2, etc., can also be locally different on the switchable filters.

[0031] The present invention also includes a first illumination device for a screen employing the first embodiment, the screen being operable in at least two operating modes B1 (for free viewing mode) and B2 (for restricted viewing mode), in which light is emitted to a viewing angle that is more limited for the observer compared to the free viewing mode, the illumination device comprising: A planar, extended backlight that emits light, and optionally constructed in a direct-emission manner (e.g., via an LED matrix), and The first switchable filter or the second switchable filter of the present invention is arranged in front of the backlight along the observation direction as described above.

[0032] As a supplementary embodiment, the present invention also includes a screen employing the first embodiment, 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. This screen includes: The aforementioned first lighting device, Furthermore, if a first linear polarizing filter is not arranged in the first switchable filter or the second switchable filter of the first lighting device, a second linear polarizing filter 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. A transmissive image reproduction device, which is arranged in front of the first switchable filter or the second 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.

[0033] Preferably, the first linear polarizing filter or the second linear polarizing filter is arranged in or as part of the transmissive image reproduction device.

[0034] The invention also includes a second screen that 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. 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 first switchable filter or the second switchable filter of the present invention, located in front of the image reproduction device 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.

[0035] Optionally, the first or second switchable filter may then be reversibly installed by the user on the image reproduction device. In this case, the filter may be sold as a so-called "aftermarket product".

[0036] Regarding the aforementioned first and second screens, when used in a passenger vehicle, advantageously, a third optical element is arranged in front of the transmissive image reproduction device along the viewing direction, the optical element comprising: Multiple light absorption transition dipole moments; here, the dye mass density is greater than 1% or even greater than 10%.

[0037] In this configuration, most transition dipole moments, at least in the first state, are oriented or oscillate around a third preferred direction, which is optional for the third optical element, with a tolerance of at most 20° (or alternatively 10°). This third preferred direction is arranged at a predetermined angle α1 to the central normal of the third optical element (e.g., α1 = 0°, α1 = ±2°, or a value (α1) > 2° may be used). The angle α1 is measured in an optional third plane containing the aforementioned central normal. The third plane is preferably perpendicular to the first plane of the first optical element. This allows light incident on the third optical element to be transmitted or at least partially absorbed depending on its incident direction relative to the third optical element and its polarization state.

[0038] The last described embodiment advantageously ensures reduced vertical transmission, thereby reducing or completely avoiding the reflection of the image content displayed on the aforementioned screen in the vehicle onto the windshield.

[0039] Furthermore, the present invention also includes a second illumination device for a screen employing the second embodiment, which is operable 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 more limited angular range compared to the free viewing mode. This illumination device includes: A planar, extended backlight that emits light within a limited angular range, and optionally constructed to emit light directly. A plate-shaped light guide located in front of the backlight along the viewing direction has an output coupling component on at least one of its large surfaces and / or within its volume. A light-emitting device arranged laterally on at least one narrow surface of the light guide, and Optional linear polarizing filter, The first or second switchable filter of the present invention, as described above, is arranged in front of the backlight (and also includes a position in front of the screen for using the lighting device) along the observation direction. In operating mode B2, the backlight is on and the light-emitting device is off, and in operating mode B1, at least the light-emitting device is on, and 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.

[0040] Within the scope of this invention, and particularly with regard to backlights, 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 significant minimization, appropriate filters are used in addition to backlights that emit light within a limited angular range. This also applies to the variants described below with light guides that emit or output most of the coupled light within a limited angular range. Unlike embodiments 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.

[0041] Furthermore, the present invention includes a third illumination device for the screen, which can operate in at least two operating modes, B1 (for free viewing mode) and B2 (for restricted viewing mode), in which light is emitted to a more limited angular range compared to the free viewing mode. A planar, extended backlight that emits light within a non-limited angular range, and optionally constructed in a direct-emission manner (e.g., via a locally dimmable LED matrix lighting unit), and A plate-shaped light guide located in front of the backlight along the viewing direction has an output coupling component on at least one of its large surfaces and / or within its volume, wherein the output coupling component outputs and couples a majority (i.e., more than half, up to 80% or 90%) of the light laterally input to at least one narrow surface of the light guide within a limited angular range. A light-emitting device arranged laterally on at least one narrow surface of the light guide, and Optional linear polarizing filter, The first switchable filter or the second switchable filter of the present invention, as described above, is arranged in front of the backlight, preferably in front of the light guide, along the observation direction. In operating mode B2, the backlight is off and the light-emitting device is on, and in operating mode B1, at least the backlight is on (as an alternative, the light-emitting device may also be optionally on), and 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.

[0042] Furthermore, the present invention includes a fourth illumination device for a screen, the illumination device being operable in at least two operating modes B1 (for free viewing mode) and B2 (for restricted viewing mode), in which light is emitted to a more limited angular range compared to the free viewing mode, the illumination device comprising: A planar extended backlight emits light within a limited angular range and (to limit the angular range of the light) includes a first optical element as described above. The backlight may optionally be constructed to emit light directly. A plate-shaped light guide located in front of the backlight along the viewing direction has an output coupling component on at least one of its large surfaces and / or within its volume. A light-emitting device arranged laterally on at least one narrow surface of the light guide, and In operating mode B2, the backlight is turned on and the light-emitting device is turned off, while in operating mode B1, at least the light-emitting device is turned on.

[0043] Advantageously, the first, second, third, and fourth lighting devices are combined with a transmissive image reproduction device (such as an LC panel) to produce a screen that can operate in at least two operating modes, B1 (for free viewing mode) and B2 (for restricted viewing mode), in which light is emitted to a more limited angular range compared to the free viewing mode.

[0044] Advantageously, the transition dipole moment of the first optical element (or, if applicable, another first, second, or third optical element) is configured as at least one, at least two, at least three, or more dichroic dyes, which are mixed with the liquid crystal in a guest-subject configuration. For permanent transition dipole moments, the liquid crystal is preferably fixed by a curing process.

[0045] 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.

[0046] In a guest-subject layout, dichroic dye molecules are typically oriented parallel to liquid crystal molecules.

[0047] As an alternative, the first optical element can be constructed as a laminate of layers of a polymer thin-film polarizer.

[0048] Furthermore, the above embodiments ensure 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 moiré effect.

[0049] The first (or second) preferred direction may, for example, form an angle of 0° to 45° with the surface normal of the first (or second) optical element. Furthermore, the first or second preferred direction may vary within a range of the surface of the first (or second) optical element. For the purposes of this invention, an average-weighted preferred direction is applicable. The first and second preferred directions may also be the same or differ in orientation by only a few degrees (maximum 10°), and both may be perpendicular to the relevant optical element. This is a preferred case. However, depending on the specific application, the first and second preferred directions may differ by more than 10°.

[0050] Furthermore, at least two such preferred directions may differ by more than 10° in the optional plane and / or the corresponding preferred directions of the transition dipole moment may be selected according to their positions in the first or second optical element.

[0051] Furthermore, advantageously, the first or second optical element is divided into different regions (A1, A2, ...) along an optional reference line, wherein for each region (A1, A2, ...), an inherent preferred region orientation can be selected, which applies to all transition dipole moments located within the region (A1, A2, ...), wherein all preferred region orientations are different in pairs and point towards the observer, with a maximum tolerance of ±10 degrees. The advantage of this arrangement is that, in a restricted viewing mode, the observer perceives the screen with the first or second switchable filter as uniformly illuminated.

[0052] 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 an 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.

[0053] 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.

[0054] Furthermore, the first or second 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, to convert circularly polarized light into (substantially) linearly polarized light upon incident light.

[0055] A first exemplary manufacturing variant of the first 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 ef) 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.

[0056] Optionally, the surface may be optically or mechanically treated to improve the subsequent quality of molecular orientation.

[0057] A mixture of dichroic dye and thermotropic liquid crystal compound or polymer is applied.

[0058] The penetration of light causes the side chains to partially condense, resulting in birefringence along the surface.

[0059] 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.

[0060] Apply the dye mixture and then photo-orient and cure the dye mixture using polarized light.

[0061] 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 birefringence or non-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 single dyes or mixtures 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.

[0062] 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.

[0063] Polymerizable liquid crystal dichroic dyes, such as azo dyes.

[0064] 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 dye typically constitutes at least 0.01% of the material of the corresponding layer in the relevant optical element by mass, preferably from 1% to 15%. In special cases, for liquid crystal dichroic dyes, the concentration can even reach 95%. The layer thickness is preferably in the range of 0.2 μm to 50 μm, more preferably in the range of 0.5 μm to 20 μm, including all boundary values. The dyes or dye mixtures used for different layers within the optical element may vary, but are not required to do so.

[0065] This applies to all embodiments of the invention: the tolerance τ is 5°≤τ≤19° or 10°≤τ≤19°, for example, τ=5° or τ=10° or τ=15° or τ=19°. For transition dipole moments N2 that account for a very small percentage (e.g., N1 / N2>50), the tolerance τ can also be greater than 19° without affecting the effectiveness of the invention.

[0066] Furthermore, advantageously, the described image reproduction device and / or lighting equipment respectively implement luminous density curves that substantially reduce the luminous density emitted or transmitted at an angle of 25° or greater (particularly measured along the horizontal plane or a first plane of the observer's viewing angle) to less than 80% of the maximum luminous density emitted or transmitted in any direction, preferably less than 60%. This enhances privacy protection within this angular range because the aforementioned luminous density curve is multiplied by the corresponding transmission curve of the switchable filter used with the described screen and / or lighting equipment. Similarly advantageously, such a luminous density curve has, for example, approximately 50% of the maximum luminous density at an angle of 45°.

[0067] In applications where an observer wearing (typically vertical) linearly polarized sunglasses looks at a screen with a first or second switchable filter, it is advantageous to arrange a λ / 4 layer in the optical path in front of the screen along the viewing direction to convert linearly polarized light into circularly polarized light. Subsequently, depending on the specific state of the first liquid crystal layer in the first switchable filter or the specific state of the second liquid crystal layer in the second switchable filter, left- or right-turned circularly polarized light is generated, which can be seen through the sunglasses (with reduced brightness). In cases where the light emitted from the sunglasses and the screen is cross-linearly polarized, without this λ / 4 layer, the observer wearing such sunglasses may be unable to see any image at all, depending on the situation.

[0068] The aforementioned switchable 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.

[0069] In principle, if the above parameters change within certain limits, the performance of the present invention can still be maintained.

[0070] 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 combinations or individually. Attached Figure Description

[0071] The present disclosure will now be described in more detail with reference to the accompanying drawings, which disclose features essential to the present disclosure. These exemplary embodiments are for illustrative purposes only and should not be construed as limiting. For example, the description of an exemplary embodiment having multiple elements or components should not be construed as requiring all of them for implementation. Rather, other exemplary embodiments may include alternative elements or components, fewer elements or components, or additional elements or components. Unless otherwise stated, elements or components of different exemplary embodiments may be combined with each other. Modifications and variations described with respect to one exemplary embodiment may also be applied to other exemplary embodiments. To avoid repetition, the same or corresponding elements in different drawings are identified by the same reference numerals and are not described again, wherein: Figure 1 This is a simplified schematic diagram of the structure of the first optical element.

[0072] Figures 2 to 5 The figures show exemplary normalized transmittance curves for light with two different polarizations (s, p) incident on a first optical element. The figures also show the corresponding values ​​of N1 / N2 for the viewing angle of the first optical element.

[0073] Figure 6a The figure shows an example comparison of normalized transmittance curves for two different polarized lights incident on a first optical element. The figure shows the viewing angle of the first optical element for two different τ values ​​when the ratio of N1 / N2 is the same, plotted using a linear scale.

[0074] Figure 6b for Figure 6a In the comparison, a logarithmic scale is used on the vertical axis.

[0075] Figure 7a The figure shows a comparison of two other exemplary normalized transmittance curves for two different polarized lights incident on the first optical element. The figure shows the viewing angle of the first optical element for two different N1 / N2 ratio values ​​when the τ value is the same, plotted using a linear scale.

[0076] Figure 7b for Figure 7a In the comparison, a logarithmic scale is used on the vertical axis.

[0077] Figure 8 and 9 More exemplary normalized transmittance curves are shown for two different polarized lights incident on a first optical element, with the figures representing the viewpoint of the first optical element, where the inequalities of the present invention are not followed.

[0078] Figure 10 A schematic diagram of an exemplary structure for a first switchable filter.

[0079] Figure 11This is a schematic diagram of an exemplary structure for a second switchable filter.

[0080] Figure 12 This is a schematic diagram of an exemplary structure of an illumination device in a first embodiment having a first switchable filter and a second switchable filter.

[0081] Figure 13 The diagram below is a schematic diagram of an exemplary structure of the screen in the first embodiment. The screen can operate in at least two operating modes, B1 and B2, and has a first switchable filter or a second switchable filter.

[0082] Figure 14 The diagram below shows an exemplary structure of the screen in the second embodiment. The screen can operate in at least two operating modes, B1 and B2, and has a first switchable filter or a second switchable filter.

[0083] Figure 15 This is a schematic diagram of an exemplary structure of the lighting device in the second embodiment, which has a first switchable filter or a second switchable filter.

[0084] Figure 16 This is a schematic diagram of an exemplary structure of the lighting device in the third embodiment, which has a first switchable filter or a second switchable filter.

[0085] Figure 17 This is a schematic diagram of an exemplary structure of the lighting device in the fourth embodiment, which has a first optical element. Detailed Implementation

[0086] These diagrams are not drawn to scale and are for illustrative purposes only. In some cases, only a selected beam is shown, while in reality, there are numerous beams. Similarly, Figure 1 Only the selected dipole moment is shown. The viewing direction should be set to top-down on the page plane whenever possible.

[0087] Figure 1 This is a schematic diagram illustrating the structure of the first optical element 1 in its permanent (or first) state. The first optical element 1 includes: Multiple optical absorption transition dipole moments (represented by arrows), where the corresponding absorption cross section is denoted by σ. abs This indicates and can be selectively applied to one wavelength, multiple selected wavelengths, or, as is commonly the case, multiple wavelengths in the human visible spectrum. Most of the transition dipole moments are permanently or at least in the first state oriented parallel to or varying around a first preferred direction (see dashed line) selectable for the first optical element 1 with an optional tolerance τ ≤ 19° (the tolerance τ applies to both directions, i.e., ±τ is added to the value of the corresponding angle). The first preferred direction is arranged at an angle α relative to the central normal (see dashed line) of the first optical element 1, wherein the angle α is measured in an optional first plane containing the aforementioned central normal, and wherein the transition dipole moments oriented parallel to the first preferred direction with tolerance τ have a density N1, and the remaining (i.e., those outside the aforementioned tolerance range) transition dipole moments have a density N2. Figure 1 A small number of exemplary selected transition dipole moments are shown, including densities N1 or N2.

[0088] This causes the light incident on the first optical element 1 to be transmitted or at least partially absorbed according to its incident direction relative to the first optical element 1 and its polarization state. Wherein, on the optical element 1, permanently or at least in the first state described above, the ratio of the corresponding densities N1 and N2 for the transition dipole moment satisfies the inequality. This allows for at least partial compensation of the larger tolerance value τ by utilizing the ratio of the correspondingly increased transition dipole moment density N1 to N2, thereby (at least) enhancing the absorption of p-polarized light incident on optical element 1 at an angle greater than 45° in the first plane.

[0089] Multiple optical absorption transition dipole moments are arranged in a layer at least 0.2 micrometers thick. Multiple elements, such as those formed by OCA (Optical Calibration Amplification), may also be present. Optically Clear Adhesive The transition dipole moment layers are separated from each other by an optically transparent adhesive and / or a substrate. The thickness of the transition dipole moment layers in all the provided layers may be, for example, from 0.2 μm to 50 μm, preferably from 0.2 μm to 20 μm, and even more preferably from 1 μm to 10 μm. In a particular embodiment, at least two transition dipole moment layers separated by at least one substrate are provided.

[0090] This invention discloses a method for overcoming manufacturing limitations related to the orientation of transition dipole moments on optical element 1, specifically by using only the ratio of the corresponding densities N1 and N2 of the transition dipole moments to permanently or at least in this first state satisfying the inequality. The optical element 1 is used to at least partially compensate for the relatively large manufacturing tolerance value τ by utilizing the ratio of the correspondingly increased transition dipole moment densities N1 and N2. In this way, not only is the absorption of p-polarized light incident on the optical element 1 at an angle greater than 45° in the first plane enhanced, but the normalized transmittance in the preferred direction or in an angular range a few degrees beyond the preferred direction is also improved.

[0091] The greater the proportion of the remaining transition dipole moments of density N2 (i.e., outside the above tolerance range), the worse the general transmittance of optical element 1 is in general (i.e., in all directions).

[0092] Approximately, Figures 2 to 9 Quantitative simulations of the normalized transmittance of the first optical element 1 are presented for various parameters. The transmittance is calculated in a manner independent of s-polarized and p-polarized light incident on the optical element 1. Normalized transmittance is shown in each figure, with dashed lines representing incident s-polarized light and solid lines representing p-polarized light. The calculation of transmittance through the absorption layer is based on Beer-Lambert's law. In addition to the layer thickness, this law also includes the product of the extinction coefficient and the concentration of the absorbing material. In this case, extinction is approximately equivalent to absorption, since absorption is produced by extremely small molecules that only weakly scatter light. The absorption coefficient is represented by α. s and α p These coefficients describe the absorption of s-polarized or p-polarized light. With regard to the ideal orientation of the molecule parallel to the first preferred direction, α... s The value reaches 0. This describes the propagation of s-polarized light in a plane including the surface normal and the first preferred direction. To describe the propagation of p-polarized light, α must be changed using Malus's law. p The following proportions are assumed in the simulation: .

[0093] first, Figure 2 The first exemplary normalized transmittance curves are shown for light of two different polarizations (s, p) incident on the first optical element 1, where the first value for the viewing angle of the first optical element 1 is N1 / N2 = 6.66. For example, when τ = 1°, the N1 / N2 ratio satisfies the aforementioned inequality. (Strictly speaking, N1 / N2 > 6.16) is sufficient. As shown in the figure, even though the transition dipole moment of p-polarized light is relatively poor, but the density ratio is relatively easy to achieve for manufacturing the first optical element 1, absorption of more than 90% can be produced at 45°.

[0094] also, Figure 3 The figures show second exemplary normalized transmittance curves for light of two different polarizations (s, p) incident on the first optical element 1, where the second value is N1 / N2 = 7 for the viewing angle of the first optical element 1. This case corresponds to the limiting value of the aforementioned inequality when τ = 10°. As shown, as before, even with a relatively poor transition dipole moment of p-polarized light, but a density ratio that is relatively easy to achieve for manufacturing the first optical element 1, absorption greater than 90% can be produced at approximately 45°.

[0095] also, Figure 4The figures represent third exemplary normalized transmittance curves for light of two different polarizations (s, p) incident on the first optical element 1, where the third value is N1 / N2 = 10 for the viewing angle of the first optical element. This case corresponds to the limiting value of the aforementioned inequality when τ = 19°. Figure 2 and 3 The much larger tolerance τ=19° in the case described above is (over) compensated here by a relatively large transition dipole moment density N1. Compared to the case where the aforementioned inequality is not satisfied, the expected absorption for p-polarized light is improved at approximately 45°.

[0096] in addition, Figure 5 The fourth exemplary normalized transmittance curves are given for light of two different polarizations (s, p) incident on the first optical element 1, where the fourth value for the viewing angle of the first optical element is N1 / N2 = 16 > 10. This case corresponds to a tightening of the limit of the aforementioned inequality when τ = 19°, where, as previously stated, at least N1 / N2 > 10 should apply. Previously... Figure 4 The relevant instructions also apply here.

[0097] Figure 6a A comparison of exemplary normalized transmittance curves for two different polarized (s, p) lights incident on a first optical element 1 is shown. The figure shows two different τ values ​​(τ=0° is a thin line, τ=10° is a thick line) plotted with respect to the viewing angle of the first optical element 1 at the same N1 / N2 ratio (e.g., N1 / N2=16.7), using a linear scale. Qualitatively, the curves for s-polarized and p-polarized light appear quite similar. Clearly, the transmittance at τ=10° is significantly reduced compared to τ=0°, because the orientation tolerance τ=10° of the transition dipole moment is larger than that of the first preferred direction: a poorly oriented transition dipole moment, i.e., a transition dipole moment with a larger tolerance, leads to α... s Relatively large.

[0098] Figure 6b for Figure 6a The comparison is performed, but a logarithmic scale is used on the vertical axis. It can be seen that, essentially from the absolute value of the viewing angle above 25°, the two parameter sets have substantially the same p-polarized light transmittance or absorptivity, but the total transmittance at τ=10° in the first preferred direction of p-polarized light and in multiple directions of s-polarized light is reduced by about 1.2 times, which is less than ideal.

[0099] and Figure 7aThe figure compares exemplary normalized transmittance curves for two different polarized (s, p) lights incident on the first optical element 1. The figure shows the viewing angle of the first optical element 1 for two different N1 / N2 ratios (16.7 is a thick line, 29.2 is a thin line) with the same τ = 10°, plotted using a linear scale. Clearly, the transmittance is significantly reduced with the smaller ratio N1 / N2 = 16.7 compared to N1 / N2 = 29.2.

[0100] Figure 7b for Figure 7a The comparison is performed, but a logarithmic scale is used on the vertical axis. It can be seen that, essentially from the absolute value of the viewing angle above approximately 30°, the two parameter sets have substantially the same p-polarized light transmittance or absorptivity, but the total transmittance N1 / N2 = 16.7 is reduced by about 1.2 times in the first preferred direction of p-polarized light and in multiple directions of s-polarized light, which is less than ideal. Therefore, Figure 6b and Figure 7b The comparison leads to the following conclusion: even at an angle with an absolute value less than about 30°, the absorption rate of p-polarized light can be achieved by reducing the tolerance τ rather than increasing the N1 / N2 density ratio.

[0101] at last, Figure 8 and 9 More exemplary normalized transmittance curves are shown for two different polarizations (s, p) incident on the first optical element 1, with the figures representing the viewing angle for the first optical element 1, where the inequalities of the present invention are not followed; the absorptivity of p-polarized light can no longer produce a transmittance of less than 10% at angles of, for example, ±45°. Figure 8 In the middle, the ratio N1 / N2=3, in Figure 9 In the above, N1 / N2 = 1.5.

[0102] Figure 10 This is a schematic diagram of an exemplary structure of the first switchable filter 5. The switchable filter includes: The aforementioned first optical element 1, (Not shown in the figure) A device for selectively generating a first electric field EF1 or a second electric field EF2, such as an ITO layer connected to a signal generator. A liquid crystal layer 3 is arranged in front of the first optical element 1 along the observation direction (here). The first electric field EF1 or the second electric field EF2 acts on the liquid crystal layer and thereby affects the polarization state of the light passing through the liquid crystal layer. Since the liquid crystal layer 3 is arranged in front of the first optical element 1 along the observation direction, the first linear polarizing filter X is located in front of the liquid crystal layer 3 along the observation direction. This causes the transmission characteristics of the first switchable filter 5 to differ between the first operating mode B1 (where a first electric field EF1 is applied) and the second operating mode B2 (where a second electric field EF2 is applied).

[0103] In cases where the transition dipole moment can change, for example, through a so-called guest-substrate liquid crystal cell, such a guest-substrate liquid crystal cell can directly correspond to the aforementioned liquid crystal layer, but it is not necessary to do so.

[0104] In a preferred embodiment, when a first electric field EF1 is applied, light penetrating the liquid crystal layer is transmitted substantially unchanged, while when a second electric field EF2 is applied, the incident light is circularly polarized or ellipsoidally polarized, or the polarization of the light is rotated (approximately) 90°.

[0105] If the liquid crystal layer 3 is arranged behind the first optical element 1 along the observation direction, then preferably linearly polarized light or elliptically polarized light is incident on the liquid crystal layer 3, 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 linearly polarizing filter in the optical path, or, in the case of using circularly polarized light, by a λ / 4 layer.

[0106] Figure 11 A schematic diagram of an exemplary structure for a second switchable filter 5a, including: The second optical element 2 includes: Multiple optical absorption transition dipole moments, where the corresponding absorption cross section is represented by σ. abs This indicates and can be selectively applied to one wavelength, multiple selected wavelengths, or, as is commonly the case, multiple wavelengths in the human visible spectrum. The transition dipole moments are composed of one or more dichroic dyes, and are respectively contained in the second liquid crystal layer 3a in a guest-host configuration. Most of these transition dipole moments are also, at least in the first state, oriented parallel to or varying around a first preferred direction selectable for the second optical element 2 with a tolerance τ ≤ 19° (the tolerance τ also applies to both directions, i.e., ±τ), wherein the second preferred direction is arranged at an angle α relative to the central normal of the second optical element 2, wherein this angle α is measured in an optional second plane containing the aforementioned central normal, and wherein the transition dipole moments oriented parallel to the second preferred direction with tolerance τ have a density N1, and the remaining transition dipole moments have a density N2 (which can be utilized). Figure 1 To illustrate the geometric proportions: optical element 1 is equivalent to the second liquid crystal layer 3a). This allows light incident on the second optical element 2 to be transmitted or at least partially absorbed, depending on its incident direction relative to the second optical element 2, its polarization state, and the state of the second liquid crystal layer 3a at the point of light incidence. (Not shown in the figure) A device for selectively generating at least a first electric field EF1 or a second electric field EF2, wherein the corresponding electric field acts on the second liquid crystal layer 3a such that the transmission characteristics of the second switchable filter 5a differ between a first operating mode B1 (where the first electric field EF1 is applied and the second liquid crystal layer 3a is in the aforementioned first state) and a second operating mode B2 (where the second electric field EF2 is applied and the second liquid crystal layer 3a is in the second state). In this second optical element 2, at least in the first state, the ratio of the corresponding densities N1 and N2 for the transition dipole moment satisfies the inequality. This allows for at least partial compensation of the larger tolerance value τ by utilizing the ratio of the correspondingly increased transition dipole moment density N1 to N2, thereby enhancing the absorption of p-polarized light incident on the second optical element 2 at an angle greater than 45° in the second plane.

[0107] The device for selectively generating at least a first electric field EF1 or a second electric field EF2 can also be advantageously designed such that different electric fields EF1, EF2 (or, depending on the situation, different electric fields EF3, EF4, etc.) are simultaneously applied to different positions on the liquid layer 3a. This enables position-dependent partial switching of the operating mode of the second switchable filter 5a.

[0108] Optionally, for the second switchable filter 5a, the ratio of the corresponding densities N1 and N2 of the transition dipole moment on its second optical element 2, at least in the second state described above, satisfies the inequality. This reduces the absorption of p-polarized light incident on the second optical element 2 at an angle greater than 45° in the second plane. In this way, higher transmittance is achieved along the second plane in the second state described above.

[0109] Advantageously, in the first switchable filter 5 and the second switchable filter 5a, the potential difference between the electrodes used to generate the first electric field EF1 and the second electric field EF2 is at least 2 volts. Other operating modes B3, B4, etc., can also be explicitly provided, whose electric fields EF3, EF4, etc., are different from those of electric fields EF1 and EF2. Furthermore, as described above, operating modes B1, B2, etc., can also be locally different on the first switchable filter 5 or the second switchable filter 5a.

[0110] also, Figure 12 A schematic diagram illustrating an exemplary structure of an illumination device employing the first embodiment, having a first switchable filter 5 or a second switchable filter 5a, 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 emits light and can optionally be constructed in a direct light-emitting manner (e.g., by means of a locally dimmable LED matrix), and As described above, a first switchable filter 5 or a second switchable filter 5a is arranged in front of the backlight 8 along the observation direction.

[0111] also, Figure 13 A schematic diagram illustrating an exemplary structure of a screen employing the first embodiment, having a first switchable filter 5 or a second switchable filter 5a, 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 first lighting device, Furthermore, if a first linear polarizing filter is not arranged in the first switchable filter 5 or the second switchable filter 5a of the first lighting device, a second linear polarizing filter P is 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, and A transmissive image reproduction device 11 is arranged in front of the first switchable filter 5 or the second switchable filter 5a 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.

[0112] Preferably, the first or second linear polarizing filter P is arranged in or as part of the transmissive image reproduction device 11, for example as a back-side (light input side) polarizing filter of the LCD panel that serves as the image reproduction device 11.

[0113] also, Figure 14 A schematic diagram illustrating an exemplary structure of a screen employing the second embodiment 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 or other image reproduction device. As described above, the first switchable filter 5 or the second switchable filter 5a of the present invention is located in front of the image reproduction device 12 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.

[0114] also, Figure 15 A schematic diagram illustrating an exemplary structure of an illumination device employing the second embodiment, having a first switchable filter 5 or a second switchable filter 5a, is shown. The screen 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 more limited angular range compared to the free viewing mode. The illumination device includes: A planar extended backlight 8b emits light within a limited angular range (represented by two nearly parallel exemplary beams) and is optionally constructed to emit light directly. A plate-shaped light guide 9 is located in front of the backlight 8b along the observation direction, and has an output coupling component on at least one of its large surfaces and / or within its volume. A light-emitting device 10 is arranged laterally on at least one narrow surface of the light guide, and Optionally (not shown in the figure), a linear polarizing filter, As described above, the first switchable filter 5 or the second switchable filter 5a is arranged along the observation direction in front of the backlight 8b (including the position in front of the screen used for the illumination device). In operating mode B2, the backlight 8b is turned on and the light-emitting device 10 is turned off. In operating mode B1, at least the light-emitting device 10 is turned on, causing the light guide 9 to emit light within a non-limited angular range. Figure 15 The example shows three nearly non-parallel beams, and 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.

[0115] Within the scope of this invention, particularly with regard to backlights or screens, 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 significant minimization, appropriate filters are used in addition to backlights that emit light within a limited angular range. This also applies to the variants described below with light guides that emit or output most of the coupled light within a limited angular range. Unlike embodiments 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.

[0116] Figure 16 A schematic diagram illustrating an exemplary structure of an illumination device employing a third embodiment, having a first switchable filter 5 or a second switchable filter 5a, is shown. The screen 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 more limited angular range compared to the free viewing mode. The illumination device includes: The planar extended backlight 8c emits light within a non-limited angular range (this point is in...). Figure 16 The example shows three nearly non-parallel beams, and can optionally be constructed in a direct-emission manner (e.g., via locally dimmable LED matrix lighting units), and A plate-shaped light guide 9c located in front of the backlight 8c along the observation direction has an output coupling component on at least one of its large surfaces and / or within its volume, wherein the output coupling component outputs and couples most of the light input laterally to at least one narrow surface of the light guide 9c (i.e., more than half, up to 80% or 90%) within a limited angular range (see two nearly parallel beams). A light-emitting device 10 is arranged laterally on at least one narrow surface of the light guide 9c, and As described above, a first switchable filter 5 or a second switchable filter 5a is arranged in front of the backlight 8c, preferably in front of the light guide 9c, along the observation direction. In operating mode B2, the backlight 8c is off and the light-emitting device 10 is on. In operating mode B1, at least the backlight 8c is on (and optionally, the light-emitting device 10 may also be on). 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.

[0117] at last, Figure 17 The schematic diagram shows an exemplary structure of an illumination device employing the fourth embodiment, which has a screen with a first optical element 1. The screen 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 more limited angular range compared to the free viewing mode. The illumination device includes: A planar extended backlight 8b emits light within a limited angular range (see two nearly parallel beams) and includes a first optical element 1 as described above to limit the angular range. This backlight may optionally be constructed to emit light directly. A plate-shaped light guide 9 is located in front of the backlight 8b along the observation direction, and has an output coupling component on at least one of its large surfaces and / or within its volume. A light-emitting device 10 is arranged laterally on at least one narrow surface of the light guide 9, and In operating mode B2, the backlight 8b is turned on and the light-emitting device 10 is turned off. In operating mode B1, at least the light-emitting device 10 is turned on, causing the light guide 9 to emit light within a non-limited angular range. Figure 17 The example shows three nearly non-parallel beams.

[0118] Advantageously, the first, second, third, and fourth lighting devices are combined with a transmissive image reproduction device (such as an LC panel) to produce a screen that can operate in at least two operating modes, B1 (for free viewing mode) and B2 (for restricted viewing mode), in which light is emitted to a more limited angular range compared to the free viewing mode.

[0119] Advantageously, the transition dipole moment of the first optical element 1 (or, if applicable, another first optical element 1 or a second optical element 2) is configured as one or more dichroic dyes, which are mixed with the liquid crystal in a guest-subject configuration. For permanent transition dipole moments, it is preferable that the liquid crystal be fixed by a curing process.

[0120] In contrast, the transition dipole moment can also be non-fixedly embedded in the liquid crystal layer as a guest-subject layout, 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.

[0121] Dichroic dye molecules are typically oriented parallel to liquid crystal molecules.

[0122] Furthermore, the above embodiments also ensure 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.

[0123] The first (or second) preferred direction may, for example, form an angle of 0° to 45° with the surface normal of the first (or second) optical element 1, 2. Furthermore, the first preferred direction may also vary within a range of the surface of the first (or second) optical element 1, 2. For the purposes of this invention, an average-weighted preferred direction is applicable.

[0124] Furthermore, the first switchable filter 5 or the second switchable filter 5a may include a polarizing filter, which is positioned upstream or downstream of the first optical element 1 or the second optical element 2 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 (approximately) linearly polarized light based on this layer.

[0125] 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 dye typically constitutes at least 0.01% of the material of the corresponding layer in the relevant optical element by mass, preferably from 1% to 15%. In special cases, for liquid crystal dichroic dyes, the concentration can even reach 95%. The layer thickness is preferably in the range of 0.2 μm to 50 μm, more preferably in the range of 0.5 μm to 20 μm, including all boundary values. The dyes or dye mixtures used for different layers within optical elements 1 and 2 may vary, but are not required to do so.

[0126] The solution of the present invention to achieve the above-mentioned objectives lies in describing an optical element in which light incident upon the optical element is transmitted or partially or completely absorbed according to its incident direction and polarization characteristics—(not primarily) according to its position. Production-related orientation tolerances are addressed through optical effects. By using a switchable filter of the optical element of the present invention, the transmission of light is affected angle-relatedly—optionally relative to a seated or standing viewer—where switching between at least two operating states is possible. In this case, the transmission behavior can be switched particularly for certain directions. Furthermore, the present invention also discloses illumination devices and screens using switchable filters.

[0127] 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.

[0128] Explanation of reference numerals in the attached figures 1: First optical element 2: Second optical element 3: First liquid crystal layer 3a: Second liquid crystal layer 5: First switchable filter 5a: Second switchable filter 8: Backlight 8b: Backlight 8c: Backlight 9: Light guide 10: Light-emitting device 11: Transmissive Image Reproduction Device 12: Image Reproduction Device P, X: Polarizing filters

Claims

1. A first optical element (1), comprising: Multiple optical absorption transition dipole moments, where the corresponding absorption cross section is represented by σ. abs This indicates and can be selectively applied to one wavelength, multiple selected wavelengths, or, as is commonly the case, multiple wavelengths in the human visible spectrum. Most of the transition dipole moments are permanently or at least in the first state oriented parallel to or varying around a first preferred direction selectable for the first optical element (1) with a tolerance τ ≤ 19°, wherein the first preferred direction is arranged at an angle α relative 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, and wherein the transition dipole moments oriented parallel to the first preferred direction with tolerance τ have a density N1, and the remaining transition dipole moments have a density N2. This causes light incident into the first optical element (1) to be transmitted or at least partially absorbed according to its incident direction and polarization state relative to the first optical element (1). The characteristic is that the ratio of the corresponding densities N1 and N2 of the transition dipole moment on the optical element (1) permanently or at least in the first state satisfies the inequality. ， The larger tolerance value τ is at least partially compensated by utilizing the ratio of the density N1 to N2 of the correspondingly increased transition dipole moment, thereby enhancing the absorption of p-polarized light incident on the optical element (1) at an angle greater than 45° in the first plane.

2. A first switchable filter (5), comprising: The first optical element (1) according to claim 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. The first electric field (EF1) or the second electric field (EF2) acts on the liquid crystal layer and thereby affects the polarization state of the light passing through the liquid crystal layer. The first linear polarizing filter (X), when the liquid crystal layer (3) is arranged in front of the first optical element (1) along the observation direction, is located in front of the liquid crystal layer (3) along the observation direction. This makes the transmission characteristics of the first switchable filter (5) different between a first operating mode B1 in which the first electric field (EF1) is applied and a second operating mode B2 in which the second electric field (EF2) is applied.

3. A second switchable filter (5a), comprising: The second optical element (2) includes: Multiple optical absorption transition dipole moments, where the corresponding absorption cross section is represented by σ. abs This indicates and can be selectively applied to one wavelength, multiple selected wavelengths, or, as is commonly the case, multiple wavelengths in the human visible spectrum. The transition dipole moment is composed of one or more dichroic dyes, and is contained in the second liquid crystal layer (3a) in a guest-host configuration. In this context, most of the transition dipole moments are also, at least in a first state, oriented parallel to or varying around a second preferred direction selectable for the second optical element (2) with a tolerance τ ≤ 19°, wherein the second preferred direction is arranged at an angle α relative to the central normal of the second optical element (2), wherein the angle α is measured in an optional second plane containing the central normal, and wherein the transition dipole moments oriented parallel to the second preferred direction with tolerance τ have a density N1, and the remaining transition dipole moments have a density N2. This allows light incident on the second optical element (2) to be transmitted or at least partially absorbed depending on its incident direction relative to the second optical element (2), its polarization state, and the state of the second liquid crystal layer (3a). A device for selectively generating at least a first electric field (EF1) or a second electric field (EF2), wherein the corresponding electric field acts on the second liquid crystal layer (3a) such that the transmission characteristics of the second switchable filter (5a) differ between a first operating mode B1 in which the first electric field (EF1) is applied and the second liquid crystal layer (3a) is in the first state, and a second operating mode B2 in which the second electric field (EF2) is applied and the second liquid crystal layer (3a) is in the second state. The characteristic is that: the ratio of the corresponding densities N1 and N2 of the second optical element (2) with respect to the transition dipole moment, at least in the first state, satisfies the inequality. ， Thus, the larger tolerance value τ is at least partially compensated by utilizing the ratio of the density N1 to N2 of the correspondingly increased transition dipole moment, thereby enhancing the absorption of p-polarized light incident on the second optical element (2) at an angle greater than 45° in the second plane.

4. The second switchable filter (5a) according to claim 3, wherein, On the second optical element (2), at least in the second state, the ratio of the corresponding densities N1 and N2 for the transition dipole moment satisfies the inequality. ， This reduces the absorption of p-polarized light that enters the second optical element (2) at an angle greater than 45° in the second plane.

5. The first switchable filter (5) according to claim 2 or the second switchable filter (5a) according to claim 3 or 4, wherein, The potential difference between the electrodes used to generate the first electric field (EF1) and the second electric field (EF2) is at least 2 volts.

6. The first switchable filter (5) according to claim 2, wherein, The first optical element (1) and / or the liquid crystal layer (3) and / or the device for 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 states.

7. A lighting device for a screen, the screen being operable in at least two operating modes B1 and B2 for a free viewing mode and a restricted viewing mode, wherein in the restricted viewing mode light is emitted to 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) that emits light, and optionally is constructed in a direct light-emitting manner, and The first switchable filter (5) according to claim 2, or the second switchable filter (5a) according to claim 3 or 4, is arranged in front of the backlight (8) along the observation direction.

8. A screen operable in at least two operating modes B1 and B2 for a free viewing mode and a restricted viewing mode, wherein in the restricted viewing mode light is emitted to 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 7, In the absence of the first linear polarizing filter (X) in either the first switchable filter (5) or the second switchable filter (5a) 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). A transmissive image reproduction device (11) is arranged in front of the first switchable filter (5) or the second switchable filter (5a) along the observation direction. The second electric field (EF2) is applied in the operating mode B2, and the first electric field (EF1) is applied in the operating mode B1.

9. The screen according to claim 8, wherein, The first linear polarizing filter (X) or the second linear polarizing filter (P) is arranged in the transmissive image reproduction device (11) or is part of the image reproduction device.

10. A screen operable in at least two operating modes B1 and B2 for a free viewing mode and a restricted viewing mode, wherein in the restricted viewing mode light is emitted to a viewing angle that is more limited for an observer than in the free viewing mode, the screen comprising: Image reproduction device (12). The first switchable filter (5) according to claim 2, or the second switchable filter (5a) according to claim 3 or 4, is arranged in front of the image reproduction device (12) along the observation direction. The second electric field (EF2) is applied in the operating mode B2, and the first electric field (EF1) is applied in the operating mode B1.

11. A lighting device for a screen, the screen being operable in at least two operating modes B1 and B2 for a free viewing mode and a restricted viewing mode, wherein light is emitted to a more limited angular range compared to the free viewing mode, the lighting device comprising: A planar extended backlight (8b) emits light within a limited angular range and may optionally be constructed in a direct light-emitting manner. A plate-shaped light guide (9) is located in front of the backlight (8b) along the viewing direction. The light guide has multiple output coupling components on at least one of a plurality of large surfaces and / or within its volume. A light-emitting device (10) arranged laterally on at least one narrow side of the light guide (9), and Optional linear polarizing filter (P) The first switchable filter (5) according to claim 2, or the second switchable filter (5a) according to claim 3 or 4, is arranged in front of the backlight (8b) along the observation direction. In operating mode B2, the backlight (8b) is turned on and the light-emitting device (10) is turned off, and in operating mode B1, at least the light-emitting device (10) is turned on, and The second electric field (EF2) is applied in the operating mode B2, and the first electric field (EF1) is applied in the operating mode B1.

12. A lighting device for a screen, the screen being operable in at least two operating modes B1 and B2 for a free viewing mode and a restricted viewing mode, wherein light is emitted to a more limited angular range compared to the free viewing mode, the lighting device comprising: A planar extended backlight (8c) emits light within a non-limited angular range and can optionally be constructed in a direct light-emitting manner. A plate-shaped light guide (9c) is located in front of the backlight (8c) along the viewing direction. The light guide has multiple output coupling components on at least one of a plurality of large surfaces and / or within its volume, wherein the output coupling components output couple most of the light input laterally to at least one narrow surface of the light guide (9c) within a limited angular range. A light-emitting device (10) arranged laterally on at least one narrow surface of the light guide (9c), and Optional linear polarizing filter (P) The first switchable filter (5) according to claim 2, or the second switchable filter (5a) according to claim 3 or 4, is arranged in front of the backlight (8c) along the observation direction. In operating mode B2, the backlight (8c) is off and the light-emitting device (10) is on, and in operating mode B1, at least the backlight (8c) is on, and The second electric field (EF2) is applied in the operating mode B2, and the first electric field (EF1) is applied in the operating mode B1.

13. A lighting device for a screen, the screen being operable in at least two operating modes B1 and B2 for a free viewing mode and a restricted viewing mode, wherein light is emitted to a more limited angular range compared to the free viewing mode, the lighting device comprising: A planar extended backlight (8b) emits light within a limited angular range and includes a first optical element (1) as claimed in claim 1, and is optionally constructed to emit light directly. A plate-shaped light guide (9) is located in front of the backlight (8b) along the viewing direction. The light guide has multiple output coupling components on at least one of a plurality of large surfaces and / or within its volume. A light-emitting device (10) arranged laterally on at least one narrow side of the light guide (9), and In the operating mode B2, the backlight (8b) is turned on and the light-emitting device (10) is turned off, and in the operating mode B1, at least the light-emitting device (10) is turned on.

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