Switchable optical filter and its use

Abstract

To provide a switchable light filter having an optical element in which light incident on the optical element is transmitted or is partially or entirely absorbed depending on its incident direction and its polarization properties, but not depending on its position.SOLUTION: A combination of a switchable light filter and an imaging display unit makes possible an anti-peeping effect that can be switched on and off. An optical element (1) comprises a first layer (S1), or the first layer (S1) and a plurality of further layers (S2, ...), each layer (S1, S2, ...) comprising a material with a plurality of light-absorbing transition dipole moments. At least in a first state, each transition dipole moment is oriented with a tolerance of at most 10° parallel to a selectable preferential direction or fluctuates around it, so that light incident on the optical element is transmitted or at least partially absorbed depending on the direction of the light incident on the layers (S1, S2, ...) and its polarization state.SELECTED DRAWING: Figure 2b

Description

Technical Field

[0001] In recent years, there has been remarkable progress in expanding the viewing angle of LCDs (Liquid Crystal Displays).

[0002] However, there are often situations where such a very large viewing area of the screen can be a drawback. Also, in mobile terminals such as notebook computers, mobile phones, and tablet PCs, information such as bank data or other personal information and confidential data can be increasingly used. Accordingly, it is necessary to control who can view these confidential data. For example, when viewing vacation photos or when selecting a wide viewing angle to share the information on the display with others for promotional purposes. On the other hand, when trying to handle image information confidentially, a small viewing angle in the non-public mode is required.

[0003] There are similar problems in vehicle manufacturing. The driver should not be distracted by the image content such as digital entertainment programs while the engine is running, but the passengers also want to enjoy them during driving. Therefore, a screen that can switch to an appropriate display mode is required.

[0004] In portable displays, additional films using microlouvers have already been used to achieve anti-peeking. However, these films are not switchable and must be manually attached first and then removed again. Also, they have to be carried separately from the display even when not needed. Furthermore, the use of such louver films has a significant drawback of light loss.

[0005] U.S. Patent Application No. US6765550B2 describes such anti-peeking using microlouvers. The biggest drawbacks here are the mechanical detachment of the filter and the light loss in the protection mode.

[0006] U.S. Patent Application No. US5993940A describes the use of a film having small strip-shaped prisms arranged at equal intervals on the surface to achieve a non-public mode, i.e., a restricted viewing mode with a narrow viewing angle range. Its development and manufacture are quite technically laborious.

[0007] In International Patent Application No. WO2012 / 033583A1, the switching between free viewing and restricted viewing is formed by operating liquid crystals in a so-called "chromonic" layer. In this case, light loss occurs and the technical cost is also quite high.

[0008] U.S. Patent Application No. US2012 / 0235891A describes a very complex backlight within the screen. Here, according to FIGS. 1 and 15, not only are a plurality of light guides used, but also other complex optical elements such as microlens elements 40 and prism structures 50 that convert light on the way from the backlight to the frontlight are used. Realizing this is expensive and technically complex, and it also involves light loss. According to a modification shown in FIG. 17 of U.S. Patent Application No. US2012 / 0235891A1, both light sources 4R and 18 generate light with a narrow irradiation angle, whereby the light from the rear light source 18 is converted into light with a large illumination angle through a complex process. This complex conversion, as already mentioned, results in a significant decrease in brightness.

[0009] According to Japanese Patent Application No. JP2007 - 155783A, a special optical surface 19 that is complex to calculate and manufacture is used to deflect light into various narrow or wide regions according to the light incident angle. These structures are similar to Fresnel lenses. Furthermore, there are interference fringes that deflect light in an undesirable direction. Therefore, it remains unclear whether a truly reasonable light distribution can be achieved.

[0010] U.S. Patent Application No. US2013 / 0308185A1 describes a special light guide formed with steps that radiates light in various directions on a large surface according to the direction of irradiation from the narrow side. When combined with a transmissive image display unit such as a liquid crystal display, a screen can be formed that can be switched between a free viewing mode and a restricted viewing mode. The drawback in this case is that the viewing restriction effect can only be generated on either the left or right or the top or bottom, and cannot be generated simultaneously on the left, right, top, and bottom as required for example in certain payment processes. In addition, even in the restricted viewing mode, afterglow can still be seen from the blocked viewing angle.

[0011] The applicant's international patent application No. WO2015 / 121398A1 describes a screen having two operating modes. In order to switch the operating mode, scattering particles are present in the volume of the corresponding light guide. However, the scattering particles made of the polymer selected there generally have the drawback that light is output from both large surfaces, and thereby about half of the effective light is radiated in the wrong direction, i.e., towards the backlight, and structurally cannot be sufficiently returned there. Furthermore, the scattering particles made of the polymer distributed in the volume of the light guide may lead to a scattering effect that reduces the peeping prevention effect in the protected operating mode in certain situations, especially at high concentrations.

[0012] The approach of the electro - optic birefringence (EDB) technology is based on the idea of using the switchable liquid crystal of an additional liquid crystal panel applied to "filter" all the light rays that do not exit from the imaging layer at a specific emission angle. The drawbacks of this technology are that the additional energy and cost are substantial, and the ±40 - degree sweet spot, i.e., the optimal line - of - sight position, is difficult to change. Also, the absorption coefficient of the liquid crystal structure is insufficient. This is because the attenuation of the light intensity for a viewing angle larger than the sweet spot rises again, and the light intensity for a viewing angle larger than ±40 degrees attenuates to up to 3% of the maximum light intensity.

[0013] A common drawback generally shared by the above methods and devices is that they significantly reduce the brightness of the basic screen and / or require complex and expensive optical elements for mode switching and / or reduce the resolution in the publicly viewable mode where viewing is unrestricted and / or generate visual artifacts in ultra-high resolution displays.

Summary of the Invention

[0014] Therefore, an object of the present invention is to disclose a switchable optical filter having an optical element in which light incident on the optical element is transmitted or partially or completely absorbed according to its incident direction and polarization characteristics, but regardless of its position. By means of a switchable optical filter using an optical element, the transmittance of light is affected according to the angle - optionally vertically for a viewer sitting or standing - and can be switched between at least two operating modes. In this case, in particular, the angular limitations in transmission in a specific direction are made switchable.

[0015] The optical element or a system based thereon can be realized inexpensively and is particularly versatile for different types of screens, enabling a switch between - at least horizontally for a standing or sitting viewer - anti-peeping, i.e., a restricted viewing mode and a free viewing mode, and ensuring that the resolution of such a screen does not substantially decrease.

[0016] The above object is solved in a first embodiment by a switchable optical filter comprising a first optical element which is not itself switchable. The optical element itself comprises a first layer or a plurality of, preferably five or more, layers in addition to the first layer. Each layer contains a material having a large number of transition dipole moments that absorb light, and each transition dipole moment is oriented parallel to or varies around a first preferred direction that can be selected for the first optical element with a tolerance of at most 10 degrees in at least a first state, such that light incident on the first optical element is transmitted or at least partially absorbed according to its incident direction on the layer and polarization state.

[0017] The transition dipole moment (also called the transition matrix element) is a quantum mechanical vector quantity corresponding to a specific transition between an initial state (usually the ground state) and a final state (usually an excited state) of a system of atoms, molecules or solids, and is equal to the electric dipole moment associated with this transition. The direction of the vector defines the polarization of the transition, and the polarization itself defines how the system interacts with an electromagnetic wave with a given polarization and, during the transition from the ground state to the excited state, for example, absorbs light in the corresponding polarization direction. The magnitude of the vector corresponds to the strength of the interaction or the transition probability.

[0018] In this case, the first preferred direction corresponds to the direction of the transition dipole moment in a predetermined propagation direction of light where absorption is equal for any polarization direction of the light. The preferred direction is the direction of the transition dipole in the medium. That is, for propagation in the medium in this direction, absorption is minimized in the anti-peeping operation mode described below.

[0019] Materials to be considered as materials in the sense of the present invention containing an orientable transition dipole moment are, for example, dichroic dyes or dye mixtures, which are combined with a carrier material that does not impair their properties, such as liquid crystals or polymers. Each layer can contain, for example, only one type of dye, and the dyes can be paired in different layers and be different from each other. However, a single layer may also contain a plurality of dyes, i.e., a dye mixture.

[0020] The switchable optical filter further includes a polarization filter disposed in front of or behind the first optical element as viewed from the incident direction, and means for selectively generating a first electric field or a second electric field. A liquid crystal layer is disposed between the first optical element and the polarization filter, and the first electric field or the second electric field acts on this liquid crystal layer, and accordingly the liquid crystal layer affects the polarization state of the light passing through the liquid crystal layer. The switchable optical filter is operable in at least two operating modes. In a first operating mode B1 having a first electric field applied and having a first sub-mode B1H and a second sub-mode B1V, on the one hand, unpolarized light incident on the switchable optical filter switchable in parallel to a first preferred direction is transmitted by at least 24%, and on the other hand, unpolarized light incident on the switchable optical filter at an angle of 30 degrees or more with respect to the first preferred direction is absorbed by at least 85%. This absorption occurs only in the first direction in the first sub-mode B1H and only in a second direction perpendicular to the first direction in the second sub-mode B1V. In contrast, in a second operating mode B2 having a second electric field applied and having a first sub-mode B1H and a second sub-mode B1V, on the one hand, unpolarized light incident on the switchable optical filter switchable in parallel to the first preferred direction is transmitted by at least 24%, and on the other hand, unpolarized light incident on the switchable optical filter (5) at an angle of 30 degrees or more with respect to the first preferred direction is absorbed by at least 85%. This absorption occurs only in the second direction in the first sub-mode B1H and only in a second direction perpendicular to the first direction in the second sub-mode B1V. As a result, the absorption directions of each of the two sub-modes B1H, B1V are different by 90 degrees with respect to the first operating mode B1 and the second operating mode B2, and thus different by 90 degrees with respect to both operating modes B1 and B2. The absorption occurs only in one direction each, and therefore light is transmitted in the other directions respectively.

[0021] In the first operating mode B1, in sub - mode B1H, absorption is performed, for example, horizontally, with respect to a seated or standing viewer or generally the eye level. In sub - mode B1V, it can be performed vertically, again with respect to a seated or standing viewer or generally the eye level. In this case, the straight line connecting both eyes defines the horizontal direction and corresponds to the first direction, and the vertical direction stands perpendicular to the horizontal direction and corresponds to the second direction. Similarly, in the second operating mode B2, absorption will be performed vertically in sub - mode B1H and horizontally in sub - mode B1V.

[0022] The configuration of this first embodiment of the switchable optical filter allows switching between the B1 mode and the B2 mode, or between the B1H mode and the B1V mode by rotating the polarization filter by 90 degrees.

[0023] In this case, for example, either the first electric field or the second electric field represents a field - free state, and the other electric field can have an absolute electric field strength greater than zero, for example, 0.5 MV / m. Depending on the design of the first optical element and the polarization filter, the field - free state can mean the presence of operating mode B1 or B1H according to the design of the first optical element and the change filter. However, it is also possible for operating mode B2 or B1V to be present in the field - free state.

[0024] In this way, the switchable optical filter of this first embodiment can cooperate with an image display unit to enable switching, for example, between vertical viewing prevention and horizontal viewing prevention (e.g., in operating mode B1, in sub - mode B1V, it is protected up / down, and in sub - mode B1H, it is protected left / right). This is the case, for example, with a laptop. In operating mode B1, in sub - mode B1V, the user can view the content together with other people sitting next to the user at approximately the same eye level. However, in sub - mode B1H, people standing beside cannot view the image content.

[0025] Substantially, the radiation angle range in which light is radiated in operation mode B1 is cut in the vertical direction in sub-mode B1V or in the horizontal direction in sub-mode B1H, and thus reduced. In operation mode B2, this assignment is reversed. In both cases, the radiation angle range is limited in one direction.

[0026] The switchable optical filter of this first embodiment can change its configuration. Table 1 below shows some important configuration examples. The first component listed in each case faces the viewer, and the other components follow suit. In this case, the abbreviation "L / R" means that the optical effect is active in the horizontal effect (in the already defined horizontal direction). This means that the polarizing filter transmits linearly polarized light in the horizontal direction and (substantially) absorbs linearly polarized light in the vertical direction. Similarly, "O / U" means that the polarizing filter transmits linearly polarized light in the vertical direction and (substantially) absorbs linearly polarized light in the horizontal direction. In contrast, the abbreviation "L / R" refers to the effect of this switchable filter that occurs in cooperation with an image display unit that can be arranged in front of or behind the switchable filter. The peeping prevention effect acts in the horizontal direction, and thus peeping from the left and right is prevented. This corresponds to operation mode B1 in sub-mode B1H of the switchable filter. Similarly, "O / U" means that for a switchable filter that cooperates with an image display unit, the peeping prevention effect acts in the vertical direction, and thus peeping from above and below is prevented. This corresponds to operation mode B1 in sub-mode B1V of the switchable filter.

[0027]

Table 1

[0028] In the example shown in Table 1, the liquid crystal layer is a nematic liquid crystal layer rotated by 90 degrees. That is, the preferred orientations of the liquid crystal on both surfaces that induce alignment and limit the liquid crystal layer are perpendicular to each other. In the case of the last row of the table, the light incident in state B1 is linearly polarized along the vertical direction (O / U) by the polarizer. Then, the linearly polarized light is rotated by 90 degrees by the liquid crystal layer and oriented in the horizontal direction (L / R). The smaller the angle between the horizontal direction and the incident direction, the smaller the light transmittance. This is the basis for the anti-peeping along the horizontal direction (L / R). In the case of state B2, a similar relationship applies, but there is no 90-degree polarization change.

[0029] Here, it is pointed out again that for the anti-peeping effect "O / U", in many practical cases, when multiple viewers view the image display unit from the side at approximately the same height, it is possible to view it normally.

[0030] The above problem is also solved by the second embodiment of the switchable optical filter. This optical filter also includes a first optical element, which is configured similarly to the first optical element of the first embodiment, but is switchable, and further, the transition dipole moments of each layer can be changed between at least a first state and a second state in terms of their directions and / or magnitudes, so that each layer can be in any of at least two different states. Here too, the polarizing filter is arranged in front of or behind the first optical element. Further, the switchable optical filter according to the second embodiment has means for selectively generating a first electric field or a second electric field. For the first optical element, the first state is generated by applying the first electric field, and the second state is generated by applying the second electric field.

[0031] In the first operation mode B1, the first electric field is applied, and the transition dipole moments of the layers of the first optical element are oriented along the first preferred direction. Generally, the electric fields of not only this switchable optical filter but also all other switchable optical filters described above or below are V RMSIt is generated by a square-wave voltage of 10 V and a frequency of 1 kHz. The first operation mode B1 includes a first sub-mode B1H and a second sub-mode B1V. In the first operation mode B1, on the one hand, at least 24% of the unpolarized light incident on the switchable optical filter that can be switched parallel to the first preferred direction is transmitted. On the other hand, at least 85% of the unpolarized light incident on the switchable optical filter according to the second embodiment at an angle of 30 degrees or more with respect to the first preferred direction is absorbed. This absorption occurs only in the first direction in the first sub-mode B1H and only in the second direction perpendicular to the first direction in the second sub-mode B1V.

[0032] In the second operation mode B3, a second electric field is applied, and the transition dipole moment of the layer of the first optical element (1) is arranged parallel to the surface of the polarization filter and perpendicular to the transmission direction of the polarization filter. In this case, at least 24% of the unpolarized light incident on the switchable optical filter that can be switched at an arbitrary angle with respect to the first preferred direction is transmitted.

[0033] Here again, for example, either the first electric field or the second electric field can represent a field-free state, and the other electric field can have an absolute electric field strength greater than zero, for example, 0.5 V / m. In this case, depending on the design of the optical element and the polarization filter, the field-free state means the existence of the operation mode B3. However, in the field-free state, it is also possible for the operation mode B1 and either the sub-mode B1H or B1V to exist.

[0034] In this way, the switchable optical filter of this second embodiment, when cooperating with an image display unit and assuming that in a first direction similar to the first embodiment is the horizontal direction and a second direction is the vertical direction, on the one hand, in the peep prevention - sub - mode B1V in the vertical direction, it is protected by a restricted emission angle range against peeping from above / below - or in the peep prevention - sub - mode B1H in the horizontal direction, it is protected by a restricted emission angle range against peeping from left / right - and on the other hand, it can be switched between a state where the emission angle range is not restricted and there is no peeping prevention effect in the operation mode B3 which is significantly larger than in the operation mode B1 having both sub - modes B1V and B1H. Here, different from the case of the first embodiment, the operation mode B3 realizes a free viewing mode in all directions.

[0035] In the third embodiment, the switchable optical filter includes a first optical element and a second optical element that are themselves non - switchable. Each of the two optical elements, the configuration and operation of which will be described below, includes a first layer, or the first layer and a plurality of other layers, preferably five or more layers. Each layer is made of a material having a large number of transition dipole moments that absorb light. Each transition dipole moment is oriented parallel to or varies around a selectable first preferred direction with a tolerance of up to 10 degrees for the first optical element and parallel to a selectable second preferred direction for the second optical element, at least in a first state. The first preferred direction and the second preferred direction differ by less than 40 degrees, preferably less than 20 degrees, particularly preferably less than 10 degrees from each other, which also includes the case where they are the same, i.e., differ by 0 degrees from each other. Light incident on the first optical element or the second optical element is transmitted or at least partially absorbed depending on the incident direction to the layer and the polarization state.

[0036] A liquid crystal layer is disposed between the first optical element and the second optical element. When an electric field acts on the liquid crystal layer, it affects the polarization state of the light passing through the liquid crystal layer according to the first electric field or the second electric field. Therefore, the switchable optical filter in the third embodiment also includes means for selectively generating the first electric field or the second electric field, such as a transparent ITO electrode (ITO - Indium Tin Oxide). Further, the switchable optical filter selectively includes a polarizing filter disposed above or below the unit including both optical elements, or does not include a polarizing filter.

[0037] In the case where a polarizing filter is present, in the first operation mode B1 having the first sub - mode B1H and the second sub - mode B1V with the first electric field applied, on the one hand, at least 24% of the unpolarized light incident on the switchable optical filter switchable parallel to the first preferred direction or the second preferred direction is transmitted, and on the other hand, at least 85% of the unpolarized light incident on the switchable optical filter at an angle of 30 degrees or more with respect to the corresponding preferred direction is absorbed. This absorption occurs only in the first direction in the first sub - mode B1H and only in the second direction perpendicular to the first direction in the second sub - mode B1V, and either the first direction or the second direction is perpendicular to the polarization direction of the polarizing filter.

[0038] In the alternative case where there is no polarizing filter, in the first operation mode B1 with the first electric field applied, at least 24% of the unpolarized light incident on the switchable optical filter at any angle is transmitted.

[0039] Regardless of whether a polarizing filter is present or not, in the second operation mode B2 with the second electric field applied, on the one hand, at least 24% of the unpolarized light incident on the switchable optical filter switchable parallel to the first preferred direction or the second preferred direction is transmitted, and on the other hand, at least 85% of the unpolarized light incident on the light guide at an angle of 30 degrees or more with respect to the corresponding preferred direction is absorbed.

[0040] As already described, the two preferred directions of the two optical elements may be the same or differ from each other by less than 40 degrees, preferably less than 20 degrees, or less than 10 degrees. When the two preferred directions are parallel to the surface normal of the optical filter configured as a laminate, for example, the transmittance is maximized in the respective preferred directions, so the radiation angle range corresponding to the viewing angle range is limited to the region around the surface normal. Therefore, when one or both of the preferred directions are tilted, the angle at which the transmittance is maximum also tilts, and accordingly, the limited viewing angle range also tilts.

[0041] When unpolarized light is incident on the first optical element and then a 90-degree polarization rotation occurs by the liquid crystal layer in the non-electric field state, the viewing angle range is limited to the left, right, up, and down. Here, when the electromagnetic field is turned on, the rotation of the polarization of light does not occur, and the limitation of the viewing angle range does not occur either, but the light is polarized perpendicular to the projection of the light incident vector onto the light incident plane. When the light incident on the first optical element is linearly polarized by a polarizing plate, the viewing angle is limited to the up, down, right, and left in the non-electric field state. At this time, when an electric field is applied, the viewing angle is limited parallel to the linear polarization of the light incident on the first optical element.

[0042] In this way, the switchable optical filter of the third embodiment cooperates with the image display unit to enable switching between two-way peeping prevention - for example, up and down peeping prevention in sub-mode B1V - and four-way peeping prevention - in operation mode B2, the viewing angle range is limited to all four directions of up / down / left / right - or, when there is no polarizing filter P, between free viewing in all directions where the viewing angle range in operation mode B1 is not limited and four-way peeping prevention in operation mode B2. The polarization state can be affected by an additional retardation plate. For example, when a λ / 4 plate is used, linear polarization is converted to circular polarization, and switching can be performed between four-way peeping prevention and unrestricted viewing.

[0043] In this case, for example, either the first electric field or the second electric field represents a field-free state, and the other electric field can have an absolute electric field strength greater than zero, for example, 0.5 MV / m. Here, the field-free state, depending on the design of both optical elements, means that the operating mode B2 exists. However, it is also possible that in the field-free state, either one of the operating mode B1 - without polarizer - or the sub-modes B1H, B1V - with polarizer - exists.

[0044] In a fourth embodiment, the switchable optical filter likewise includes a switchable first optical element and a second optical element, which is different from the third embodiment. In this case, each of the two optical elements includes a first layer, or the first layer and a plurality of other layers, preferably five or more layers. Each layer is made of a material having a large number of transition dipole moments that absorb light. Each transition dipole moment is oriented parallel to or varies around a selectable first preferred direction for the first optical element (1) with a tolerance of at most 10 degrees in at least a first state, and parallel to a selectable second preferred direction for the second optical element (2). The light incident on the first optical element or the second optical element is transmitted or at least partially absorbed depending on the incident direction on the layer and the polarization state. Different from the third embodiment, here the transition dipole moments of each layer can be changed between at least a first state and a second state in terms of their orientation and / or magnitude, putting each layer into one of at least two different states.

[0045] Also in the fourth embodiment of the switchable optical filter, the switchable optical filter includes means for selectively generating a first electric field or a second electric field. For each of the two optical elements, a first state is generated by applying the first electric field, and a second state is generated by applying the second electric field. Both electric fields are applied to the two optical elements simultaneously, but here too, one of the two electric fields can again mean a field-free state. An optically anisotropic layer is disposed between the two optical elements and rotates the polarization direction of light passing through the alignment layer by 90 degrees. This alignment layer is made of, for example, a uniaxial twisted material (also called a Schadt-Helfrich cell) similar to a TN cell (TN = Twisted Nematic) and / or an optically active material.

[0046] Optionally, a polarization filter may or may not be disposed above or below both optical elements (understood as a unit). The polarization filter is not essential, but can improve the performance of the switchable optical filter. The polarization of the polarization filter and the polarization of the incident light must coincide.

[0047] In this fourth embodiment, in the first operating mode B1 in which the first electric field is applied, non-polarized light incident on the switchable optical filter at an arbitrary angle is transmitted at least 24%. In the first operating mode B1, the transition dipole moments of the two optical elements are oriented perpendicular to each other. When a polarization filter is present, the polarization filter transition dipole element of the polarization filter is oriented parallel to the transition dipole moment of the switchable optical element closest to the polarization filter. In the second operating mode B2 in which the second electric field is applied, on the one hand, non-polarized light incident on the switchable light guide parallel to the first preferred direction or the second preferred direction is transmitted at least 24%. On the other hand, non-polarized light incident on the switchable light guide at an angle of 30 degrees or more with respect to the corresponding preferred direction is absorbed at least 85%. In the operating mode B2, when a polarization filter is present, its transition dipole moment and the transition dipole moment of the switchable optical element closest to the polarization filter are oriented perpendicular to each other, and the transition dipole moments of the two optical elements are oriented parallel to each other.

[0048] In this way, the switchable optical filter of this fourth embodiment cooperates with the image display unit to enable switching between free viewing in all directions in the public or free operation mode B1 and four-way peeping prevention in the up, down, left, and right preferred directions in the non-public or restricted operation mode B2 with a restricted viewing angle range or emission angle range compared to the operation mode B1. When non-polarized light hits the switchable optical filter in the non-public operation mode B2, light that is not incident almost parallel in the preferred direction preferably oriented parallel in the operation mode B2 is absorbed. In the public operation mode B1, linearly polarized light is transmitted.

[0049] In a preferred embodiment of the first or third embodiment, at least one polarization compensation layer is arranged in front of and / or behind the liquid crystal layer. Thereby, on the one hand, it is possible to compensate for the difference in the change of the polarization of the light incident perpendicular to the surface normal and, on the other hand, the light incident at a predetermined angle.

[0050] Preferably, the preferred directions each form an angle between 0 degrees and 45 degrees with respect to the surface normal of the first layer. This covers the normal viewing angle - for example, on a screen having a switchable optical filter.

[0051] For special applications, in any of the above-described embodiments, the switchable optical filter can be divided into a plurality of separately switchable segments, each enabling local switching between possible operating states. In cooperation with the image display unit, this can, for example, switch between a non-public mode with peeping prevention for only a part of the screen and a public mode without peeping prevention effect, i.e., for free viewing, meaning that the complementary screen part is permanently in the peeping prevention mode or the public mode. Furthermore, there can be a plurality of such segments geometrically separated from each other, which can also be switched separately or together between the operating modes.

[0052] Furthermore, each layer of the first optical element and / or the second optical element (if present) is preferably configured aperiodically. This reduces the occurrence of visual artifacts such as moiré patterns that may be uncomfortable for viewers of the corresponding screen.

[0053] The present invention acquires special significance by forming a screen by combining the above-described switchable optical filter with an image display unit. Such a screen includes, in addition to the switchable optical filter as described above, an image display unit disposed behind or in front of the switchable optical filter as viewed by the viewer. Since the operating state of the above-described switchable optical filter is transferred to the screen without problems, the screen can also be in the various operating modes described above. Depending on the design in which the switchable optical filter is used, for example, at least in the first operating state for a free public viewing mode in the horizontal direction where the radiation angle range or the viewing angle range is not restricted, and in a restricted non-public viewing mode in the horizontal direction where the radiation angle range or the viewing angle range is restricted compared to the free viewing mode in the horizontal direction. A viewer located outside this restricted viewing angle range can only perceive the image content displayed on the screen in the free viewing mode.

[0054] Advantageously, the image display unit corresponds to an LCD panel in which one polarizing filter corresponds to the polarizing filter of the switchable optical filter. This can be the front or back polarizing plate in the LCD configuration. More advantageously, the switchable optical filter is disposed between the LCD panel and its backlight and can be switched between a first operating state for a free viewing mode and a second operating state for a restricted viewing mode. This is because the light from the backlight is, for example, converged horizontally at times and not converged at times when switched horizontally by the switchable optical filter. Here, the term "converge" does not mean focusing like a lens, but means narrowing the irradiation range or the transmission range by the angle.

[0055] Alternatively, the image display unit can be an OLED, a surface conduction electron emission device display (SED), a field emission display (FED), a micro LED display, or a vacuum fluorescent display (VFD), and a switchable optical filter is disposed in front of it. Since the switchable optical filter is effective regardless of the type of the image display unit, any other type of screen is also taken into consideration.

[0056] Such a screen is advantageously used in mobile terminals, automobiles, aircraft, ships, payment terminals, access systems, etc. In this case, in order to protect highly confidential data, it can be switched between the above modes. That is, it is possible to display in such a way that only one viewer can perceive it, or to display the image content to a plurality of viewers simultaneously.

[0057] Hereinafter, the optical element according to the present invention that solves the problems and can be used as the first optical element and / or the second optical element in particular in the four embodiments of the above-described switchable optical filter will be described in more detail again, and possible configurations will be shown.

[0058] Such an optical element includes a first layer, or a first layer and a plurality of other layers, preferably five or more layers, and each layer in the context of the present invention can correspond to, for example, a molecular layer. However, it may also be a mechanically separated layer of each appropriate material. Each layer is made of a material having a large number of transition dipole moments that absorb light. Possible materials are as already mentioned when explaining the optical element of the switchable optical filter at the beginning. Each transition dipole moment is oriented parallel to or varies around a preferred direction that can be selected in at least a first state with a tolerance of at most 10 degrees with respect to the preferred direction, and as a result, the light incident on the optical element is transmitted or at least partially or completely absorbed depending on its incident direction and polarization state with respect to the layer. Preferably, the preferred directions each form an angle between 0 degrees and 45 degrees with respect to the surface normal of the first layer.

[0059] The absorption of light, i.e., the absorption, depends on the relative orientation of the transition dipole moment - and thus is also specific to the layer thickness where the transition dipole moment exists - and the polarization of the incident light. The density of the above transition dipole moment, its intensity, or the refractive index within the layer of the optical element can vary depending on the implementation. In the case of a passive, i.e., non-switchable, optical element, the volume density of the transition dipoles may approach 100%.

[0060] To simplify the modeling of transmission, it is assumed that the transition dipole moments within the optical element are oriented parallel to the light incidence plane of the optical element, and the preferred direction corresponds to the central perpendicular of the optical element. In this case, the incidence plane refers not to the surface of the optical element but to the plane in which the propagation direction of the light wave lies, and the surface of the optical element and the incidence plane are perpendicular to each other. The light wave has a transverse magnetic vibration component and a transverse electric vibration component as a transverse wave, and both components are perpendicular to each other and perpendicular to the propagation direction. The light incident on the optical element is initially not polarized for the entire light wave. That is, the vibration directions of the transverse electric component - and correspondingly the transverse magnetic component - are statistically distributed. Thus, when the transition dipole moment oriented perpendicular to the surface of the optical element reaches the surface of the optical element, the light interacts with the transition dipole moment of the optical element or the substance contained therein and is polarized. At this time, the vibration component within the incidence plane is absorbed. Therefore, the light polarized parallel to the incidence plane, i.e., the light polarized in the transverse magnetic or p-polarized state, is absorbed, while the light polarized perpendicular to the incidence plane - i.e., parallel to the surface of the optical element - i.e., the light polarized in the transverse electric or s-polarized state, is completely transmitted. Accordingly, unpolarized light that does not pass through the optical element parallel to the transition dipole moment is at least partially s-polarized when the transition dipole moment oriented parallel to the light incidence plane passes through the optical element. When the preferred direction does not coincide with the central perpendicular, o-polarization (ordinary polarization) is considered instead of s-polarization, and e-polarization (extraordinary polarization) is considered instead of p-polarization.

[0061] This characteristic is essential in all embodiments of the present invention and constitutes the relationship between the means and effects of the essential invention. Hereinafter, the transmission of p-polarized light is modeled by the incident intensity I0(α). The transmittance of the light passing through the absorption layer is described by Lambert-Beer's law.

[0062]

Number

[0063] Here, α is the propagation direction with respect to the surface normal, d(α) is the optical path length depending on the propagation direction, N is the number of absorbing molecules, and σabs(α) is the absorption cross section depending on the incident angle. Using Snell's law of refraction, the propagation angle α in the medium can be calculated from the incident angle β. Next, from the equations of the transition dipole moment and the change in the optical path, the following equation is derived.

[0064]

Number

[0065] Each layer is configured periodically or aperiodically according to the application, and the aperiodic configuration is advantageous in terms of avoiding visual artifacts.

[0066] In a preferred embodiment, each transition dipole moment is oriented in its respective preferred direction within a tolerance range of up to 10 degrees around this preferred direction. There is also the highest transmittance along the preferred direction. As a selectable plane - principle - in at least one of the layers, at least two such preferred directions preferably differ by 10 degrees or more. Thereby, a plurality of preferred directions can be defined within one layer, all of which can be directed towards a point in space, for example, towards the viewer, and different orientations within the layer can be achieved, for example, by photo - alignment, by appropriately adjusting the material properties. For this purpose, liquid crystals are combined with photoreactive substances. The incident polarized light simultaneously aligns the molecules and induces a photoreaction. By controlling the polarization, the orientation of the molecules can be affected.

[0067] The micro louvre filters described in the prior art (also called "view control filters VCF" or "light control filters LCF") utilize geometric optics. By alternately and periodically arranging transparent layers and absorption layers, almost all of the incident light propagating at a large angle with respect to a predetermined direction is absorbed. Here, the position of the absorber is controlled. In contrast, in the optical element according to the present invention, since the absorption cross-section of the molecules changes depending on the propagation direction, the light transmittance changes when the propagation direction is different. Therefore, in the present invention, instead of the position of the absorber, the orientation (direction) of the absorber is controlled. In other words, the present invention is based on the direction-dependent absorption of light rays when passing through the optical element according to the present invention, basically regardless of the position of the light rays, once the preferred directions given to the transition dipole moments are disregarded. This applies to both the non-switchable optical element according to the present invention described above and the switchable embodiments described later.

[0068] Regarding the switchability of the optical action of the optical element according to the present invention, that is, a switchable optical element, the transition dipole moments of each layer can be changed between at least a first state and a second state in terms of their orientation and / or magnitude, so that each layer can be in any of at least two different states. Possible embodiments of the switchable optical element or each layer therein are based on, for example, liquid crystals and / or dyes or dye mixtures, which are arranged in so-called "vertically aligned cells" or liquid crystal cells homogeneously oriented on the surface and can be rotated between at least two states therein. In this case, since the transition dipole moments that absorb light also rotate, at least two operating states can be taken. In particular, in such an embodiment, two or more states, for example three or eight states, can be obtained, and it is conceivable that the optical actions are different for each. Another embodiment of the liquid crystal cell is also conceivable. In particular, an electric field is used to rotate the liquid crystal in this case. In this case, for example, either the first electric field or the second electric field can represent the field-free state, and each of the other electric fields can have an absolute electric field strength greater than zero, for example 0.5 MV / m.

[0069] In this case, such a first state corresponds to the above-mentioned conditions, and at least a second state is different from it, and thus has at least one different preferred direction.

[0070] In such an active (i.e., switchable element) optical element, it is conceivable that the volume density of the transition dipole moment based on liquid crystal is between 0.1% and 90%. Alternatively, in a switchable optical element embedded in a liquid or in each layer thereof, embodiments in which the transition dipole moment is electro-wetted are also conceivable. In this way, in particular, the density of the transition dipole moment can be changed, but not limited to this.

[0071] Furthermore, the optical element is divided into a plurality of separately switchable segments, and local switching is possible between at least two different states respectively. Within the framework of the switchability between at least two states, it can be implemented such that, in particular, the respective transmission maxima between at least two states are in different directions respectively.

[0072] Furthermore, it is preferable that the respective preferred directions of the transition dipole moments can be selected according to their positions in the respective layers.

[0073] In another preferred embodiment of the optical element, each layer is divided into various regions along selectable reference lines on the respective layer, and a unique region preference direction can be selected for each region. This region preference direction corresponds to all the transition dipole moments of the corresponding layer within the region, and all the region preference directions are pairwise different from each other and are oriented towards the viewer's direction with a tolerance of up to ±10 degrees. Thus, within one layer and within each corresponding region, all the transition dipole moments are oriented parallel to the applicable preference direction therein with a tolerance of up to ±10 degrees. Advantageously, each layer is configured aperiodically in its structure, which can reduce or prevent the occurrence of disturbing visual artifacts. This arrangement has the advantage that the viewer perceives the screen as being uniformly illuminated in a restricted viewing mode. The viewer perceives the screen as inhomogeneous due to the angular dependence of the luminance if the transition dipoles are constant across the entire filter.

[0074] The possibility of easily manufacturing the optical element according to the present invention as described above lies in the optical element being a stack of a large number of polymer film polarizers. In this case, it is formed as a stack of layers of polymer film polarizers. Alternatively or in combination, the optical element can also be manufactured by photo-aligning molecules or particles.

[0075] The optical element material preferably contains at least one type of dye, preferably a dichroic dye mixture. The at least one type of dye contains dye molecules, and advantageously each dye molecule is associated with a transition dipole or a transition dipole moment. That is, each dye molecule corresponds to a transition dipole or a transition dipole moment. Usually, in an LC dye mixture, the dye has a mass fraction of, for example, 0.01% to 10%, preferably 0.1% to 5% in the material of each layer. The thickness of the layer is preferably in the range of 0.2 μm to 50 μm, suitably 0.5 μm to 20 μm, including all the respective boundary values. The dyes or dye mixtures of the various layers can be different.

[0076] Furthermore, it is also possible that the material of the optical element contains liquid crystal and / or is mixed with liquid crystal. This may be different for each layer when there are multiple layers.

[0077] As a preferred embodiment, a mixture of liquid crystal and at least one kind of dye, particularly at least one kind of dichroic dye mixture, is applied to each layer. Dichroic dyes or dye mixtures include, for example, azomethine dyes, indigoid and thioindigoid dyes, merocyanine, azulene, quinophthalone dyes, perylene dyes, phthaloperylene dyes, dioxazine dyes, triphenodioxazine dyes, quinoxaline dyes, triazine dyes, tartrazine, azo dyes, anthraquinone dyes, which are considered. The production of liquid crystal dye mixtures is described, for example, in US Patent Application US4,695,131A. Furthermore, in order to achieve the transition dipole moment or, when liquid crystal is present, its homogeneous surface orientation, the surface closing the outer layer is treated, such as brushing.

[0078] Generally, a polarizing filter can advantageously be in front of or behind the optical element in the viewing direction, particularly when used in a switchable optical filter. The polarizing filter helps to determine or analyze the polarization characteristics of the light passing through the optical element, and preferably it is desirable to always be present. The maximum transmittance of the optical element is respectively given in a direction parallel to the polarization direction of the polarizing filter in principle. It is also possible to have two such polarizing filters, each arranged in front of or behind the optical element in the viewing direction and oriented substantially parallel to each other with respect to their linear polarization directions, thereby improving the anti-peeping effect in a restricted viewing mode.

[0079] A lighting device having an optical element as described above is also within the scope of the present invention. Such a lighting device can be operated in at least two operating modes, namely an operating mode B1 for a free viewing mode and an operating mode B2 for a restricted viewing mode. The restricted viewing mode differs from the free viewing mode in that light is radiated towards the viewer within a restricted angular range. In this case, a viewer outside the restricted angular range does not see the light emitted from the lighting device (the same also applies to the screen described below), whereas in the free viewing mode the viewer perceives the light emitted from the lighting device or the screen. However, in this case, the viewer is within the basically naturally restricted emission angle range of the lighting device or the screen in the free viewing mode - considerably larger than the emission angle range of the restricted viewing mode. The restriction can be made in the upward, downward, right and / or left directions depending on the application.

[0080] The lighting device has a planar extended backlight that emits light including an optical element as described in detail above. The lighting device has a plate-shaped light guide located in front of the backlight in the viewing direction, and this light guide has output elements on at least one large surface and / or within its volume, and the light guide is at least 40%, preferably at least 70% transparent to the light emitted from the backlight. The light source is arranged laterally on at least one narrow side of the light guide. Further, a linear polarizing filter is arranged in front of the backlight or in front of the light guide in the viewing direction, whereby the light emitted from the backlight and passing through the polarizing filter has its propagation direction restricted. In operating mode B2, the backlight is turned on and the light source is turned off. In operating mode B1, at least the light source is turned on, and in operating mode B1 it does not matter whether the backlight is on or off.

[0081] Finally, the above-described optical element can also be used for a screen that can be operated in at least two operating modes already mentioned in connection with the lighting device as already shown, namely the first operating mode B1 for the free viewing mode and the operating mode B2 for the restricted viewing mode. Such a screen has a planar extended backlight that emits light and includes the optical element as described above. The screen further includes a plate-shaped light guide placed in front of the backlight in the viewing direction, and this light guide has output elements on at least one large surface and / or within its volume. The light guide is at least 40%, preferably at least 70% transparent to the light emerging from the backlight. The light source is arranged laterally on at least one narrow side of the light guide. Further, a linear polarizing filter is arranged in front of the backlight or in front of the light guide in the viewing direction, whereby the light emerging from the backlight and passing through the polarizing filter has its propagation direction restricted. Further, a transmissive image display unit is arranged in front of the light guide in the viewing direction. The polarizing filter can be arranged within the image display unit, for example, as in the case of an LC display, and in particular can be part of this image display unit. In the operating mode B2, the backlight is on and the light source is off. In the operating mode B1, at least the light source is on, and it does not matter whether the backlight is on or off in the operating mode B1.

[0082] More generally, a screen having at least one of the above-described optical elements, or the above-described arrangement, and an image display unit disposed behind or in front of the optical element as viewed by a viewer is also included in the scope of the present invention. Advantageously, the image display unit corresponds to an LCD panel in which one polarizing filter corresponds to the above-described polarizing filter. This may be a front or back polarizing plate in the LCD configuration. Alternatively, the image display unit can be an OLED, a surface conduction electron emission device display (SED), a field emission display (FED), a micro LED display, or a vacuum fluorescent display (VFD), and the optical element is disposed in front of it. Since this optical element is effective regardless of the type of the image display unit, any other type of screen is also contemplated. Such a screen is advantageously used in a mobile terminal, an automobile, an aircraft, a ship, a payment terminal, or an access system. In the case of a switchable optical element - at that time - it is possible to switch between the above-described operation modes to protect highly confidential data, that is, to display it so that it can be perceived only by one viewer, or alternatively, to display the image content to a plurality of viewers simultaneously. Further, the switchable or non-switchable optical element in the above-described embodiment can also be used together with a static image or a dynamic image display unit such as an LCD panel, for example, to make the promotional content visible only within a limited viewing range.

[0083] Basically, as long as the above-described parameters vary within a certain range, the performance of the present invention is maintained.

[0084] It should be understood that the above-described features and the features described below can be used not only in the described combinations but also in other combinations or alone without departing from the scope of the present invention.

Brief Description of the Drawings

[0085] Hereinafter, the present invention will be described in detail by way of examples with reference to the accompanying drawings that also disclose features essential to the present invention. These examples are for illustrative purposes only and should not be construed as limiting the invention. For example, the description of an embodiment having a number of elements or members should not be construed as meaning that all of these elements or members are necessary for implementation. Rather, other embodiments may include alternative elements or members, fewer elements or members, or additional elements or members. The elements or members of different embodiments can be combined with each other unless otherwise specified. Modifications and variations described for one embodiment are applicable to other embodiments as well. To avoid repetition, the same or corresponding elements in different figures are denoted by the same reference numerals and will not be described repeatedly.

[0086]

Fig. 1a

[0087]

Fig. 1b

[0088]

Fig. 1c

[0089]

Fig. 2a

[0090]

Fig. 2b

[0091]

Fig. 2c

[0092]

Fig. 3

[0093]

Fig. 4

[0094]

Fig. 5

[0095]

Fig. 6

[0096]

Fig. 7a

Fig. 7b

Fig. 7c

[0097]

Fig. 8

[0098]

Fig. 9

[0099]

Fig. 10

[0100]

Fig. 11

Fig. 12

Fig. 13

Fig. 14

Fig. 15

DETAILED DESCRIPTION OF THE INVENTION

[0101] The drawings are not to scale and are only schematic diagrams.

[0102] Figure 1a shows a schematic diagram of an exemplary non-switchable optical element 1. The optical element 1 includes at least one layer S1, and this layer S1 is made of a material having a large number of electric transition dipole moments (schematically shown here as small vertical lines) that absorb light and are oriented parallel to or vary around a preferred direction (here perpendicular to the surface of the layer S1) that can be selected at least in a first state. Thereby, the above-mentioned preferred direction forms an angle between 0 degrees and 45 degrees with respect to the surface normal of the layer S1. As a result, the light incident on the optical element is transmitted, or partially or completely absorbed, depending on the incident direction and polarization characteristics with respect to the layer S1.

[0103] The optical element 1 can be manufactured, for example, by laminating a large number of polymer film polarizers and / or by optically orienting molecules or particles. Depending on the implementation, the density of the above-mentioned electric transition dipoles in the layer S1 can vary. In the case of a passive polarizer, the volume density may approach 100%.

[0104] The material of the optical element 1 including a transition dipole moment can also contain at least one type of dye, particularly one type of dye molecule, preferably at least one type of dichroic dye or a dichroic dye mixture. In this case, advantageously, the dye molecule can correspond to the transition dipole moment. Typically, the dyes have a mass fraction of 0.01% - 30%, preferably 0.1% - 15% or 5%, or 0.01% - 10% in the materials of the respective layers S1, S2,.... The thickness of the layer is preferably in the range of 0.2 μm - 50 μm, suitably in the range of 0.5 μm - 20 μm. The dyes or dye mixtures of the various layers can be different.

[0105] The layers S1, S2,... including a transition dipole moment can also contain a liquid crystal or a polymer and / or can be mixed with a liquid crystal. Preferably, the layers S1, S2,... contain a mixture of a liquid crystal or a polymer and at least one type of dye, particularly at least one type of dichroic dye mixture.

[0106] The optical element 1 represents an anti-glare filter for linearly polarized light. Therefore, here, a polarizing filter P is provided that linearly polarizes the light incident from below parallel to the plane of the drawing. However, the polarizing filter P does not change the direction of light propagation. Two possible light propagation directions are indicated by two thick arrows. For example, light having a (diagonal) direction of about 30 degrees or more with respect to the center line perpendicular to the layer S1 in the preferred direction is absorbed by the optical element 1 based on the action of the transition dipole moment. Finally, as indicated by the only arrow at the top of the drawing, only the light incident substantially along the preferred direction, here perpendicular to the optical element 1, remains after passing through the optical element 1. Depending on the application, each layer S1, S2,... is configured periodically or aperiodically in its structure.

[0107] The absorption of light (i.e., absorption) depends on the absolute value of the transition dipole moment and thus essentially on the layer thickness of the material having the transition dipole moment. Depending on the implementation, the density of the transition dipole moment, its strength, or the refractive index within the layers S1, S2, ... can vary. In the case of the passive, i.e., non-switchable, optical element 1, the volume density of the transition dipoles can approach 100%.

[0108] Regarding this, the drawings in FIGS. 11 to 15 show an optical simulation for illustrating the optical action of the optical element 1. FIG. 11 is a graph showing the normalized transmittance of light when passing through the optical element 1 according to FIG. 1, where it is plotted against the horizontal measurement angle from -90 degrees to +90 degrees. A strong absorption effect can be clearly confirmed at angles of ±25 degrees or more. This simulation is for a layer thickness d = 0.5 mm of the optical element 1, a refractive index n = 1.5 of the material, a molar concentration M = 0.01 molm -3 , and an exemplary molar extinction coefficient ε = 12700 m 2It was assumed to be mol-1. The thickness and concentration can be changed in proportion to each other. For example, if the thickness is reduced to one-tenth and the concentration is increased by a factor of 10, the same transmittance can be obtained. In FIG. 12, the situation according to FIG. 11 is plotted logarithmically on the vertical axis for the range of values that are mainly important in use. Using such parameters, it can be seen that the transmittance has already decreased to about 1% at ±25 degrees and to only about 0.001% at ±40 degrees. In FIG. 13, the conditions assumed for the refractive index n in FIG. 11 were calculated for n = 1.0; 1.3; 1.5, and n = 1.7. It can be seen that the transmittance depending on the angle is more restricted as the refractive index of the material of layer S1 is smaller. Furthermore, FIG. 14 shows that the normalized transmittance of the optical element 1 according to the situation in FIG. 11 changes with respect to the thickness of the optical element 1. In this case, the layer thicknesses were calculated as d = 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, and 0.5 mm. As expected, the restriction of the transmittance depending on the angle becomes stronger as the layer thickness increases. Finally, FIG. 15 shows the normalized transmittance depending on the angle for three selected parameter sets (1. n = 1.0 and d = 0.2 mm; 2. n = 1.5 and d = 0.5 mm; 3. n = 1.7 and d = 0.65 mm). All three parameter sets produce very similar optical effects.

[0109] In contrast, a microrouver filter known in the prior art (also called "view control filter VCF" or "light control filter LCF") utilizes geometric optics. By alternately arranging transparent layers and absorption layers periodically, almost all of the light propagating at a large angle with respect to a predetermined direction is absorbed. Here, the position of the absorber is controlled. In contrast, in the optical element 1, since the absorption cross-section area of the molecules changes depending on the propagation direction, the transmittance of the light changes when the propagation direction is different. Therefore, not the position of the absorber but especially the orientation of the absorber is controlled. In other words, the action of the optical element 1 is based on the direction-dependent absorption when the light beam passes through and is basically independent of the position of the light beam. This applies to both the non-switchable optical element described above and the switchable embodiments described later.

[0110] Regarding the switchability of the optical action of the optical element 1, i.e., the switchable optical element 1, the electric transition dipole moments that absorb light in each layer S1, S2, ... can change their orientation and / or absolute value to put each layer S1, S2, ... into at least two different states. Possible embodiments of the switchable optical element 1 or each layer S1, S2, ... therein are based on, for example, liquid crystals or phosphors, which are arranged in so-called "vertically aligned cells" or liquid crystal cells homogeneously oriented on the surface and can be rotated between at least two states therein. In this case, since the electric transition dipole moment that absorbs light also rotates, at least two operating states can be taken. In particular, in such embodiments, it is conceivable that two or more states, for example three or eight states, are obtained, each having a different optical action. Another embodiment of the liquid crystal cell is similarly conceivable.

[0111] In addition to this, FIG. 1b shows a schematic diagram of the switchable optical element in the first state, and FIG. 1c shows a schematic diagram of the switchable optical element in the second state.

[0112] In this exemplary case, it is assumed that the incident light is p-polarized, i.e., polarized parallel to the plane of incidence (see FIG. 1b). When the transparent electrodes E1 and E2 are not charged, i.e., an electric field EF1 of 0 V / m (no electric field) is generated, the liquid crystal molecules and dye molecules (here formed as layers S1, S2, S3 for example) indicated by dots here are oriented along the surfaces of the electrodes E1 and E2. This can be achieved by an appropriate combination of surface functionalization and liquid crystal and is known in the prior art. For the light propagating in the plane of the figure and s-polarized, the polarization of the light and the transition dipole moment of the liquid crystal are always oriented perpendicular to each other. Therefore, no absorption occurs, and the propagation directions of the light with s-polarization shown above and below the substrate S pass through the switchable optical element 1 without being hindered.

[0113] As shown in FIG. 1c, when electrodes E1 and E2 are charged, i.e., when an electric field EF2 > 0 V / m is generated, the liquid crystal rotates within layers S1, S2, and S3. When the voltage, and thus the electric field strength EF2, exceeds a certain threshold, the liquid crystal molecules, and thus the dye molecules (if present), are oriented almost parallel to the electric field lines of the electric field EF2. Thereby, light is absorbed according to the angle α formed between the light propagation direction and the surface normal of layer S1. The absorption increases as the angle α increases. The extinction of the light's electric field is proportional to sin(α). Basically, controlling the orientation of the dye molecules has the advantage of controlling the viewing prevention axis thereby or performing a defined light effect. In the state according to FIG. 1b, the transition dipole moment is oriented perpendicular to the polarization of the incident light, and in the state according to FIG. 1c, it is oriented parallel to the perpendicular incidence of the light. In such a switchable optical element, the volume density of the dye can be considered to be 0.1% - 20% based on the liquid crystal, and in some cases, up to 90% at most.

[0114] FIG. 2a shows a schematic diagram of another non-switchable optical element 1. This optical element 1 includes (merely by way of example here) layer S1, which is made of a material having a large number of transition dipole moments (schematically indicated by small lines in layer S1 in FIG. 2a) that absorb light. Each transition dipole moment is oriented parallel to or varies around a respective preferred direction (schematically indicated by thick arrows here) that can be selected for each such transition dipole according to the position of such a transition dipole within layer S1, at least in a first state, with a tolerance of up to 10 degrees, and at least two such preferred directions differ by 10 degrees or more within a selectable plane (here the plane shown in the figure). Thereby, it is achieved that the light incident on the optical element 1 is transmitted, partially or completely absorbed, according to the incident direction on its layer S1 and the polarization characteristics, and the maximum transmittance for each transition dipole is in a respective preferred direction selected for the position within that layer S1, with a tolerance of up to 10 degrees being allowed in that case.

[0115] Unlike FIG. 1, the optical element 1 shown in FIG. 2 is designed such that the layer S1 is divided into various regions A1, A2, A3, A4, A5 along a selectable reference line (here, its lower edge), and for each region A1, A2, ···, a unique region preference direction (see thick arrows) corresponding to all the transition dipole moments of the layer S1 within that region A1, A2, ··· is selected. In this case, all the region preference directions are pairwise different from each other, and they are all - with a tolerance of up to ±10 degrees - directed towards the direction of the viewer 6. Therefore, within the layer S1 and within each corresponding region A1, A2, ···, all the transition dipole moments are oriented parallel to the corresponding region preference direction there with a tolerance of up to ±10 degrees. Since the transmittance on the optical element 1 can be defined, this optical element 1 can be particularly advantageously used for forming anti-peeping measures.

[0116] Regarding the switchability of the optical action of the optical element 1, i.e., regarding the switchable optical element 1, the electric transition dipole moments that absorb light in each layer S1, S2, ··· can change their orientation (alignment) and / or absolute value to put each layer S1, S2, ··· into at least two different states.

[0117] In addition to this, FIG. 2b shows a schematic diagram of a first section of the switchable optical element in the first state - this corresponds to A1 in FIG. 2a -, and FIG. 2c shows a schematic diagram of a second section of the switchable optical element in the first state - this corresponds to A5 in FIG. 2a -. Here, for example, there are three layers S1, S2, S3. The liquid crystal mixed with the dichroic dye mixture is shown here as elliptical elements in the layers S1, S2, S3. The black elliptical elements represent the dye molecules, and the white elliptical elements represent the liquid crystal in a highly simplified manner. Also, the inclination of the ellipse represents the spatial orientation. The substrate S can be glass or polymer or other transparent materials.

[0118] Each of the transparent electrodes E1 and E2, for example, an indium tin oxide layer (ITO layer), serves to control the alignment of the liquid crystal mixed with the mixed dye. However, different alignments of the liquid crystal molecules, and thus the dyes, are preferably achieved by different surface functionalizations. Here, mechanical and optical processes are considered. The alignment of the liquid crystal and dye mixture shown in FIG. 2b substantially corresponds to the alignment following the preferred direction of section A1 in FIG. 2a. The alignment of the liquid crystal and dye mixture shown in FIG. 2c substantially corresponds to the alignment following the preferred direction of section A5 in FIG. 2a. Light incident on the optical element 1 from below is maximally transmitted in the direction of the corresponding preferred direction of the transition dipole in the case of the state shown in FIG. 2b, and is partially or completely absorbed in other directions. This also applies mutatis mutandis to the state shown in FIG. 2c.

[0119] Regarding the behavior of p-polarized and s-polarized light when incident on the optical element in relation to the applied electric fields EF1 and EF2, refer to the explanations for FIGS. 1b and 1c applied here. However, the transition dipole moments are oriented differently, and in the medium, o-polarized light is dominant instead of s-polarized light, and e-polarized light is dominant instead of p-polarized light.

[0120] FIG. 3 shows a schematic diagram of a configuration having a switchable optical element 1 according to the embodiments of FIGS. 1b and 1c and FIGS. 2b and 2c. Here, there are two linear polarizing filters P (one of which is optional) on the outer surface, and their polarization directions are oriented substantially (i.e., with a tolerance of several degrees) parallel to each other. On the inner side - that is, the side where the polarizing filters P face each other - there is one transparent substrate S each, followed by electrodes E1 and E2 further inward. The alignment layer 4 facing inward from there serves to align the liquid crystal mixed with at least one type of dichroic dye to form the internal layers S1, S2,.... The transition dipole moment is formed here by at least one type of dichroic dye. Basically, in the configuration of the optical element 1 of all the above-described variations, an additional retardation film can be used to further adapt the polarization state.

[0121] The square-wave voltage applied between electrodes E1 and E2 preferably has an effective value of 0 V to 20 V. The alignment layer 4 is, for example, a surface (such as glass or polymer treated by brushing) treated to achieve a transition dipole moment or a uniform surface alignment of the liquid crystal. Thereby, for example, the states shown in FIGS. 2b and 2c can be created.

[0122] Finally, FIG. 4 is an exemplary graph for comparing the normalized transmission behavior (solid line) of the optical element 1 measured at various angles according to FIGS. 2 and 3 with that of a louver filter from the prior art (dashed line). The horizontal axis plots the respective measurement angles, and the vertical axis plots the normalized transmittance. In the continuous curve, an approximate so-called "top-hat" distribution can be seen for the transmission behavior of the exemplary optical element 1. That is, the transmittance is stable at at least 80% over a wide angular range of approximately -17 degrees to +17 degrees. Here, the total half-value width is approximately 40 degrees. Thereby, good transmittance homogeneity is obtained for a viewer with respect to a viewing angle change of ±15 degrees, and thereby good perceived homogeneity is also realized in illumination or image display in cooperation with the image display unit. In contrast, for the exemplary louver filter from the prior art cited for comparison, its normalized transmission behavior is shown by the dashed line in FIG. 4, but the half-value width is merely as small as approximately 35 degrees, and it does not have a "top-hat" like distribution, and the transmittance is greater than that of the optical element 1 in the angular ranges of -30 degrees to 25 degrees and +25 degrees to +30 degrees, so the anti-peeping effect is also poor.

[0123] This optical element can be used particularly in a switchable optical filter 5. FIG. 5 shows a third embodiment of such a switchable optical filter 5 - the name "third" was chosen before "first" and "second" in order to maintain consistency with the general description of the present invention. This optical filter 5 includes a first optical element 1 and a second optical element 2. Both optical elements 1 and 2 are themselves non-switchable, i.e., static. The preferred directions of the transition dipole moments of both optical elements differ from each other by 40 degrees or less, preferably 20 degrees or less, particularly preferably 10 degrees or less, and the first preferred direction for the first optical element 1 and the second preferred direction for the second optical element 2 are selectable. In this example, both preferred directions are, illustratively, parallel to each other and correspond to the central perpendicular of the switchable optical filter 5 in the plane of the drawing. A switchable liquid crystal layer 3 is disposed between the optical elements 1 and 2, and depending on the electric fields EF1 or EF2 acting on these optical elements, it affects or does not affect the polarization characteristics of the light passing through the optical elements. In the drawing, a polarization filter P is disposed below the optical elements 1 and 2 as viewed by the viewer 6, but it could also be disposed above the optical elements 1 and 2. Although not shown, the means for selectively generating the first electric field EF1 and the second electric field EF2 are, for example, electrodes disposed above and below the liquid crystal layer 3.

[0124] In a first operation mode B1 having a first sub-mode B1H and a second sub-mode B1V in which a first electric field EF1 is applied, on the one hand, non-polarized light incident on the switchable optical filter 5 that can be switched parallel to the first or second preferred direction is transmitted by at least 24%, and on the other hand, non-polarized light incident on the switchable optical filter 5 at an angle of 30 degrees or more with respect to the preferred direction is absorbed by at least 85%. This absorption occurs only in the first direction in the first sub-mode B1H and only in a second direction perpendicular to the first direction in the second sub-mode B1V, and either the first direction or the second direction is perpendicular to the polarization direction of the polarization filter P. When used in a display screen, the first direction may correspond to the horizontal direction and the second direction may correspond to the vertical direction, where "horizontal" means a line parallel to the line between the viewer's eyes. For example, horizontal is parallel to the S1 layer or the lower edge of the screen, and vertical is parallel to the left or right edge.

[0125] In the second operation mode B2 in which the second electric field EF2 is applied, on the one hand, at least 24% of the non-polarized light incident on the optical filter 5 that can be switched parallel to the first preferred direction or the second preferred direction is transmitted, and on the other hand, at least 85% of the non-polarized light incident on the optical filter 5 that can be switched at an angle of 30 degrees or more with respect to the preferred direction is absorbed.

[0126] A modified example of the third embodiment of the switchable optical filter 5 without using the polarizing filter P is shown in FIG. 6. The behavior of this modified example in the operation mode B2 is the same as that of the switchable optical filter 5 described with reference to FIG. 5. Here, in the first operation mode B1 in which the first electric field EF1 exists, at least 24% of the non-polarized light incident on the optical filter (5) that can be switched at an arbitrary angle is transmitted.

[0127] In this way, the switchable optical filter 5 of the third embodiment cooperates with the image display unit to enable switching between two-way peeping prevention and four-way peeping prevention (for example, upper / lower protection B1V and upper / lower / left / right protection B2) when there is a polarizing filter P, or to enable switching between free viewing in all directions and four-way peeping prevention (for example, free viewing and upper / lower / left / right protection B2) when there is no polarizing filter P.

[0128] In this case, for example, either the electric field EF1 or the electric field EF2 represents a field-free state, and it is possible for the other electric field EF2 or EF1 to have an absolute electric field strength greater than zero, for example, 0.5 MV / m. Here, depending on the design of the optical elements 1 and 2, the field-free state may mean the existence of the operation mode B2. However, also in the field-free state, when there is a polarizing filter P having either the sub-mode B1H or B1V, the operation mode B1 may also exist.

[0129] Figs. 7a to 7c show schematic views of the polarization state of light based on the switchable optical filter according to Fig. 6. Fig. 7a shows the polarization state in the public mode corresponding to the operation mode B1 with an unrestricted viewing angle range. Light with a viewing angle of 30 degrees or more is tangentially polarized, and light incident vertically is linearly polarized. The preferred directions correspond to the respective central perpendiculars. Fig. 7c shows the polarization state in the restricted viewing mode. Here, for example, light with an incident angle of 30 degrees or more is highly attenuated, while light incident vertically passes through without a change in the polarization state.

[0130] Depending on the direction or orientation of the transition dipole moment, the light is polarized with respect to the incident angle. That is, the linear polarization of the light is always perpendicular to the direction of the origin in the viewing angle space, and in this example, the origin is the central perpendicular. This state is shown in Fig. 7a and corresponds to after the light has passed through the non-switchable optical element 1. Light with a small angle is only slightly polarized. Ideally, light incident vertically is not absorbed, that is, the polarization state remains unchanged.

[0131] Now, when the light transitions from the optical element 2 to the liquid crystal layer 3, whether the polarization state of the light changes, how it changes, or whether the polarization state remains unchanged depends on the state of the liquid crystal layer 3. For example, when the polarization rotation in the liquid crystal layer 3 is turned off in the electric field-free state EF1, the above-described state does not change. Even after passing through the liquid crystal layer 3 and then through the non-switchable optical element 1, the transmittance does not substantially change. If there is a polarization filter P above the optical element 1 or below the optical element 2, either the sub-mode B1H or B1V is achieved depending on the design. If this polarization plate is absent, the operation mode B1 is realized.

[0132] On the other hand, for example, when the polarization rotation in the liquid crystal layer 3 is turned on by applying an electric field EF2 > 0 V / m, the polarization generally rotates by 90 degrees. The polarization state is shown in FIG. 7b. Here, the polarization state after passing through the optical element 2 and the polarization rotation liquid crystal layer 3 is shown. As a result, within another propagation range of light by the optical element 1, all light propagating at an angle greater than 25 degrees or about 30 degrees is extinguished. This corresponds to the operation mode B2 and is shown in FIG. 4c.

[0133] FIG. 8 shows a principle diagram of the switchable optical filter 5 in the fourth embodiment. This switchable optical filter 5 includes two switchable optical elements 1 and 2, and each of the two optical elements has a first layer S1, or the first layer S1 and a plurality of other layers S2,.... Similar to the optical element of the third embodiment, each layer S1, S2,... includes a material having a large number of transition dipole moments that absorb light, and each transition dipole moment is oriented parallel to or varies around a selectable first preferred direction for the first optical element with a tolerance of at most 10 degrees in at least the first state. As a result, the light incident on the first optical element 1 or the second optical element 2 is transmitted or at least partially absorbed depending on the incident direction on the layers S1, S2,... and its polarization state.

[0134] However, different from the third embodiment, here the optical elements 1 and 2 are switchable. That is, the transition dipole moments of each layer S1, S2,... can be changed between their orientation and / or magnitude between the first state and at least the second state, so that each layer S1, S2,... can be in any of at least two different states. The switchable optical filter 5 in this embodiment has means for selectively generating a first electric field EF1 or a second electric field EF2. For each of the two optical elements 1 and 2, applying the first electric field EF1 generates the first state, and applying the second electric field EF2 generates the second state. In an example according to the fourth embodiment, the first electric field EF1 is applied to the first optical element 1, and the second electric field EF2 is applied to the second optical element 2.

[0135] Optionally, a polarizing filter can be arranged above or below the optical element 1 summarized as a unit. This polarizing filter is not essential, but it can improve the performance of the switchable optical filter 5. The polarization of the polarizing filter P and the polarization of the incident light must match. An optically anisotropic layer 7 is arranged between the two optical elements 1 and 2, and the polarization direction of the light passing through this optically anisotropic layer 7 is rotated by 90 degrees. The optically anisotropic layer 7 can be, for example, a layer having liquid crystal or a half-wave plate. The means for generating both the electric fields EF1 and EF2 are not shown.

[0136] When the first electric field EF1 is applied in the operation mode B1 for the free viewing mode, non-polarized light incident on the switchable optical filter 5 at any angle is transmitted by at least 24%. In the first operation mode B1, the transition dipole moments of the two optical elements 1 and 2 are oriented perpendicular to each other. When there is a polarizing filter P, the polarization filter transition dipole element of the polarizing filter P is oriented parallel to the transition dipole moments of the switchable optical elements 1 and 2 closest to the polarizing filter P.

[0137] On the other hand, when the second electric field EF2 is applied in the second operation mode B2 for the restricted viewing mode, on the one hand, at least 24% of the non-polarized light incident on the light guide 5 that can be switched parallel to the first preferred direction or the second preferred direction is transmitted, and on the other hand, at least 85% of the non-polarized light incident on the light guide 5 that can be switched at an angle of 30 degrees or more with respect to the corresponding preferred direction is absorbed. In the operation mode B2, the transition dipole moment of the polarizing filter P (if any) and the transition dipole moments of the switchable optical elements 1 and 2 closest to this polarizing filter P are oriented perpendicular to each other, and the transition dipole moments of both optical elements 1 and 2 are oriented parallel to each other. Here too, the preferred direction preferably corresponds to the perpendicular bisector of the center of the switchable optical filter 5 shown in the plane of FIG. 8. This, as already described with respect to the third embodiment, applies simultaneously in both the horizontal and vertical directions when the corresponding orientation of the switchable optical filter 5 is such that, in particular, the horizontal is parallel to the lower edge of the S1 layer and the vertical is parallel to the left or right edge of the S1 layer.

[0138] In this way, the switchable optical filter 5 of this fourth embodiment, in cooperation with the image display unit, enables switching between free viewing in all directions and prevention of peeping (free viewing B1 and up / down / left / right protection B2).

[0139] A first embodiment of the switchable optical filter 5 is shown as a schematic diagram in FIG. 9. This embodiment also has a non-switchable first optical element 1 including the first layer S1, or the first layer S1 and a plurality of other layers S2,.... Each layer S1, S2,... is made of a material having a large number of transition dipole moments that absorb light. Each transition dipole moment is oriented parallel to or varies around the first preferred direction selectable with respect to the first optical element 1 with a tolerance of at most 10 degrees, at least in the first state. As a result, the light incident on the first optical element 1 is transmitted or at least partially absorbed depending on the incident direction and polarization state to the layers S1, S2, ···.

[0140] A polarization filter P is disposed in front of or behind the first optical element 1. Means for selectively generating the first electric field EF1 or the second electric field EF2 are not shown either. A liquid crystal layer 3 is disposed between the first optical element 1 and the polarization filter P, and the first electric field EF1 or the second electric field EF2 acts on the liquid crystal layer 3, and accordingly the liquid crystal layer affects the polarization state of light passing through the liquid crystal layer.

[0141] In this first embodiment, in the first operation mode B1 having the first sub-mode B1H and the second sub-mode B1V, when the first electric field EF1 is applied, on the one hand, at least 24% of the non-polarized light incident on the optical filter 5 that can be switched parallel to the first preferred direction is transmitted, and on the other hand, at least 85% of the non-polarized light incident on the optical filter 5 that can be switched at an angle of 30 degrees or more with respect to the first preferred direction is absorbed. This absorption occurs only in the first direction in the first sub-mode B1H and only in the second direction perpendicular to the first direction in the second sub-mode B1V. In this case, the first preferred direction is preferably parallel to the central perpendicular of the optical filter 5 that can be switched in the illustrated plane. Regarding the positions of the first direction and the second direction, the description made with respect to the third embodiment can be applied mutatis mutandis.

[0142] In the second operation mode B2 having the first sub-mode B1H and the second sub-mode B1V, when the second electric field EF2 is applied, on the one hand, at least 24% of the non-polarized light incident on the optical filter 5 that can be switched parallel to the first preferred direction is transmitted, and on the other hand, at least 85% of the non-polarized light incident on the optical filter 5 that can be switched at an angle of 30 degrees or more with respect to the first preferred direction is absorbed. This absorption occurs only in the second direction in the first sub-mode B1H and only in the second direction perpendicular to the first direction in the second sub-mode B1V. As a result, the absorption directions in each of the two sub-modes B1H and B1V are different by 90 degrees with respect to the first mode B1 and the second mode B2, respectively.

[0143] Here, different from what was described above, both operation modes are operation modes having a restricted viewing mode, and the peeping prevention can be switched between two directions perpendicular to each other, for example, the horizontal direction and the vertical direction. The configuration of the first embodiment of this switchable optical filter 5 can switch the configuration between the sub-modes B1V and B1H by rotating the polarizing filter P by 90 degrees.

[0144] Here too, for example, either the first electric field EF1 or the second electric field EF2 represents a field-free state, and the other electric field EF2 or EF1 can have an absolute electric field strength greater than zero, for example, 0.5 MV / m. Depending on the design of the optical element 1 and the polarizing filter P, the field-free state may mean that the sub-mode B1H exists. However, it is also possible for the sub-mode B1V to exist in the field-free state.

[0145] In this way, the switchable optical filter 5 of this first embodiment can cooperate with the image display unit to switch between vertical peeping prevention and horizontal peeping prevention (up / down protection B1V and left / right protection B1H). For example, in a laptop, in the sub-mode B1V, the user can view the content together with other people who are next to the user and have approximately the same eye level, but in the sub-mode B1H, people on the side cannot view the image content. The switchable optical filter 5 of this third embodiment can change its configuration as described above.

[0146] Finally, FIG. 10 shows, as a schematic diagram, a second embodiment of the switchable optical filter 5. The first optical element 1 is configured similarly to the optical element 1 of the first embodiment, but is different in that it is switchable. That is, the transition dipole moments of the respective layers S1, S2, ... can be changed between their first state and at least a second state in terms of their orientation and / or magnitude, so that each of the layers S1, S2, ... can be in any of at least two different states. A polarization filter P is disposed in front of or behind the first optical element 1. Means for selectively generating the first electric field EF1 or the second electric field EF2 are not shown in the drawings either, and the first state is generated by applying the first electric field EF1 to the first optical element 1, and the second state is generated by applying the second electric field.

[0147] In the first operation mode B1 having the first sub-mode B1H and the second sub-mode B1V, in which the first electric field EF1 is applied and the transition dipole moments of the layers S1, S2, ... of the first optical element 1 are oriented along the first preferred direction, on the one hand, non-polarized light incident on the switchable optical filter 5 switchable parallel to the first preferred direction is transmitted by at least 24%, and on the other hand, non-polarized light incident on the switchable optical filter 5 switchable at an angle of 30 degrees or more with respect to the first preferred direction is absorbed by at least 85%. This absorption occurs only in the first direction in the first sub-mode B1H and only in the second direction perpendicular to the first direction in the second sub-mode B1V. In this case, the first preferred direction is preferably also parallel to the central perpendicular of the switchable optical filter 5 in the plane shown. Regarding the positions of the first direction and the second direction, the description made for the third embodiment can be applied mutatis mutandis.

[0148] In the second operation mode B2 in which the second electric field EF2 is applied, the transition dipole moments of the layers S1, S2, ... of the first optical element (1) are oriented parallel to the surface of the polarization filter P - also called the substrate in this context - and perpendicular to the transmission direction of the polarization filter P. Non-polarized light incident on the switchable optical filter (5) switchable at an arbitrary angle with respect to the first preferred direction is transmitted by at least 24%.

[0149] Also in this case, for example, either the electric field EF1 or the electric field EF2 represents a field-free state, and the other electric field EF2 or EF1, respectively, can have an absolute electric field strength greater than zero, for example 0.5 MV / m. Depending on the design of the optical element 1 and the polarizing filter P, the field-free state may mean that the operating mode B2 exists. However, also in the field-free state, it is possible that an operating mode B1 having either the sub-mode B1H or B1V exists.

[0150] In this way, the switchable optical filter 5 of this second embodiment can cooperate with the image display unit to switch between preventing peeking in the vertical or horizontal direction and a state without a peeking prevention effect (upper / lower protection B1V or left / right protection B1H and no peeking prevention B3).

[0151] For special applications, the switchable optical filter - regardless of which of the above embodiments - can be divided into a plurality of separately switchable segments, enabling local switching between the possible operating states. This allows, in cooperation with the image display unit, for example, only a part of the screen to be switched between peeking prevention and free viewing without a peeking prevention effect, and the complementary screen part to be permanently in the peeking prevention mode or the public mode. Furthermore, there are a plurality of such segments that are geometrically separated from each other and can be switched separately or together between the operating modes.

[0152] As already mentioned, the above-described switchable optical filter 5 can form a screen in combination with the image display unit. Such a screen can be operated in at least one first operating mode B1V and / or B3 for a horizontally free viewing mode and at least one second operating mode B1H and / or B2 for a horizontally restricted viewing mode, and has one of the switchable optical filters 5 of the four above-described embodiments and an image display unit arranged behind or in front of the switchable optical filter 5 as seen from the viewer 6.

[0153] Advantageously, the image display unit has one polarizing filter corresponding to the LCD panel of the polarizing filter. This can be the front or rear polarizing plate in the LCD configuration. More advantageously, a switchable optical filter is arranged between the LCD panel and its backlight to switch between a first operating state B3 (or B1V) for a free viewing mode and a second operating mode B1H or B2 for a restricted viewing mode. This is because the light of the backlight is converged horizontally (B2 or B1H) by the switchable optical filter at times and not converged (B3 or B1V) at times. Here, the term "converge" does not mean focusing like a lens, but means narrowing the irradiation range or transmission range by the incident angle.

[0154] Such a screen is advantageously used in mobile terminals, automobiles, airplanes, ships, payment terminals, or access systems, etc. In this case, in order to protect highly confidential data, it can be switched between the above modes. That is, it can be displayed so that only one viewer can perceive it, or alternatively, the image content can be displayed to multiple viewers simultaneously.

[0155] In the above-described optical element, the light incident on and passing through this optical element is transmitted, partially or entirely absorbed according to its incident direction and polarization characteristics. The switchable optical filter using such an optical element affects the transmission of light according to the angle (optionally vertically), and can switch between at least two operating states of a free viewing mode and a restricted viewing mode with respect to the viewing angle range of the viewer. In this case, in particular, the switching of the angle limit in the transmission in a specific direction is possible. This optical element or a system based on it can be implemented at low cost, and is particularly versatile for various different types of screens, enabling switching between at least horizontal viewing prevention and a free viewing mode, and at this time, the resolution of such a screen basically does not decrease.

[0156] The above-described invention can be advantageously applied anywhere where the display and / or input of confidential data is performed in cooperation with an image display unit, for example, PIN input and data display at an ATM or a payment terminal, or password input, or viewing of e-mails on a mobile terminal. As described above, the present invention can also be applied to a passenger car, and it is possible to selectively prevent the display of disturbing image content to the driver or passengers. The above embodiments can also be described as follows, but are not limited thereto. [Configuration 1] A switchable optical filter (5), - A first optical element (1) including a first layer (S1) or the first layer (S1) and a plurality of other layers (S2,...), Each layer (S1, S2,...) includes a material having a large number of transition dipole moments that absorb light, Each transition dipole moment is oriented parallel to or varies around a first preferred direction selectable for the first optical element (1) with a tolerance of at most 10 degrees, at least in a first state, and as a result, Light incident on the first optical element (1) is transmitted or at least partially absorbed according to the incident direction with respect to the layer (S1, S2,...) and its polarization state, A first optical element (1), - A polarization filter (P) disposed in front of or behind the first optical element (1) as viewed from the incident direction, - Means for selectively generating a first electric field (EF1) or a second electric field (EF2), - A liquid crystal layer (3) disposed between the first optical element (1) and the polarization filter (P), wherein the first electric field (EF1) or the second electric field (EF2) acts on the liquid crystal layer (3), thereby affecting the polarization state of the light passing therethrough accordingly, And as a result, - In a first operating mode B1 having a first sub-mode B1H and a second sub-mode B1V in which the first electric field (EF1) is applied, at least 24% of the unpolarized light incident on the switchable optical filter (5) parallel to the first preferred direction is transmitted, while at least 85% of the unpolarized light incident on the switchable optical filter (5) at an angle of 30 degrees or more with respect to the first preferred direction is absorbed, and this absorption occurs only in a first direction in the first sub-mode B1H and only in a second direction perpendicular to the first direction in the second sub-mode B1V, - In a second operation mode B2 having the first sub-mode B1H and the second sub-mode B1V with the second electric field (EF2) applied, at least 24% of the non-polarized light incident on the switchable optical filter (5) parallel to the first preferred direction is transmitted, while at least 85% of the non-polarized light incident on the switchable optical filter (5) at an angle of 30 degrees or more with respect to the first preferred direction is absorbed. This absorption occurs only in the second direction in the first sub-mode B1H and only in the second direction perpendicular to the first direction in the second sub-mode B1V. As a result, the absorption direction in each of the two sub-modes B1H and B1V is 90 degrees different with respect to the first operation mode B1 and the second operation mode B2, respectively. A switchable optical filter (5). [Configuration 2] A switchable optical filter (5), - A first optical element (1) including a first layer (S1) or a first layer (S1) and a plurality of other layers (S2,...), Each layer (S1, S2,...) includes a material having a large number of transition dipole moments that absorb light, Each transition dipole moment is oriented parallel to or varies around the first preferred direction selectable for the first optical element (1) with a tolerance of at most 10 degrees in at least a first state. As a result, The light incident on the first optical element (1) is transmitted or at least partially absorbed according to the incident direction on the layers (S1, S2,...) and its polarization state, The transition dipole moments of each layer (S1, S2,...) can be changed between their first state and at least a second state in terms of their orientation and / or magnitude, so that each layer (S1, S2,...) can be in any of at least two different states, A first optical element (1), - A polarization filter (P) disposed in front of or behind the first optical element (1), - Means for selectively generating a first electric field (EF1) or a second electric field (EF2), wherein the first state is generated by applying the first electric field (EF1) to the first optical element (1), and the second state is generated by applying the second electric field (EF2). Means, having, as a result, - In a first operation mode B1 having a first sub-mode B1H and a second sub-mode B1V, in which the first electric field (EF1) is applied and the transition dipole moments of the layers (S1, S2,...) of the first optical element (1) are oriented along the first preferred direction, at least 24% of the non-polarized light incident on the switchable optical filter (5) parallel to the first preferred direction is transmitted, while at least 85% of the non-polarized light incident on the switchable optical filter (5) at an angle of 30 degrees or more with respect to the first preferred direction is absorbed, and this absorption occurs only in a first direction in the first sub-mode B1H and only in a second direction perpendicular to the first direction in the second sub-mode B1V. -In a second operation mode B3, in which the second electric field (EF2) is applied and the transition dipole moments of the layers (S1, S2,...) of the first optical element (1) are oriented parallel to the surface of the polarizing filter (P) and perpendicular to the transmission direction of the polarizing filter (P), a switchable optical filter (5) through which at least 24% of the non-polarized light incident on the switchable optical filter (5) at an arbitrary angle with respect to the first preferred direction is transmitted. [Configuration 3] A switchable optical filter (5), - which is both an optical element of a first optical element (1) and a second optical element (2), each including a first layer (S1) or a first layer (S1) and a plurality of other layers (S2,...), each layer (S1, S2,...) includes a material having a large number of transition dipole moments that absorb light, each transition dipole moment is oriented parallel to or varies around a selectable first preferred direction for the first optical element (1) and a selectable second preferred direction for the second optical element (2) with a tolerance of at most 10 degrees in at least a first state, and as a result, the light incident on the first optical element (1) or the second optical element (2) is transmitted or at least partially absorbed depending on the incident direction on the layer (S1, S2,...) and its polarization state, the first preferred direction and the second preferred direction of the transition dipole moments differ by less than 40° from each other, a first optical element (1) and a second optical element (2), - A liquid crystal layer (3) disposed between the first optical element (1) and the second optical element (2), wherein a first electric field (EF1) or a second electric field (EF2) acts on the liquid crystal layer (3), thereby affecting the polarization state of the light passing therethrough accordingly. - Means for selectively generating the first electric field (EF1) or the second electric field (EF2). It has - Optionally, it has a polarization filter (P) disposed above or below both of the optical elements (1, 2), or does not have a polarization filter (P). As a result, - When the polarization filter (P) is present, the first electric field (EF1) is applied. In the first operation mode B1 having the first sub-mode B1H and the second sub-mode B1V, at least 24% of the unpolarized light incident on the switchable optical filter (5) parallel to the first preferred direction or the second preferred direction is transmitted, while at least 85% of the unpolarized light incident on the switchable optical filter (5) at an angle of 30 degrees or more with respect to the corresponding preferred direction is absorbed. This absorption occurs only in the first direction in the first sub-mode B1H and only in the second direction perpendicular to the first direction in the second sub-mode B1V. Either the first direction or the second direction is perpendicular to the polarization direction of the polarization filter (P). - Or, when there is no polarization filter (P), in the first operation mode B1 in which the first electric field (EF1) is applied, at least 24% of the unpolarized light incident on the switchable optical filter (5) at any angle is transmitted. - In the second operation mode B2 in which the second electric field (EF2) is applied, regardless of the presence of the polarization filter (P), at least 24% of the unpolarized light incident on the switchable optical filter (5) parallel to the first preferred direction or the second preferred direction is transmitted, while at least 85% of the unpolarized light incident on the switchable optical filter (5) at an angle of 30 degrees or more with respect to the corresponding preferred direction is absorbed. A switchable optical filter (5). [Configuration 4] A switchable optical filter (5), - The first layer (S1), or the first layer (S1) and a plurality of other layers (S2,...), are both optical elements of the first optical element (1) and the second optical element (2) each containing. Each layer (S1, S2,...) contains a material having a large number of transition dipole moments that absorb light. Each transition dipole moment is oriented parallel or fluctuates around with a tolerance of at most 10 degrees with respect to a selectable first preferred direction for the first optical element (1) and with respect to a selectable second preferred direction for the second optical element (2), at least in the first state, and as a result, light incident on the first optical element (1) or the second optical element (2) is transmitted or at least partially absorbed depending on the incident direction and the polarization state with respect to the layer (S1, S2, ...), the transition dipole moments of the respective layers (S1, S2, ...) can be changed in their orientation and / or magnitude between the first state and at least a second state, such that each layer (S1, S2, ...) can be in any of at least two different states, a first optical element (1) and a second optical element (2), - means for selectively generating a first electric field (EF1) or a second electric field (EF2), wherein the first state is generated by applying the first electric field (EF1) to each of the two optical elements (1, 2), and the second state is generated by applying the second electric field (EF2), - an optically anisotropic layer (7) disposed between the two optical elements (1, 2), the optically anisotropic layer (7) being an optically anisotropic layer (7) that rotates the polarization direction of light passing through it by 90 degrees, having, - optionally, a polarization filter (P) disposed above or below the two optical elements (1, 2), or not having a polarization filter (P), and as a result, - in a first operating mode B1 in which the first electric field (EF1) is applied, at least 24% of the unpolarized light incident on the switchable optical filter (5) at an arbitrary angle with respect to the switchable optical filter (5) is transmitted, and in the first operating mode B1, the transition dipole moments of the two optical elements (1, 2) are oriented perpendicular to each other, and when a polarization filter (P) is present, the polarization filter transition dipole element of the polarization filter (P) is oriented parallel to the transition dipole moment of the switchable optical element (1, 2) closest to the polarization filter (P), - In a second operation mode B2 in which the second electric field (EF2) is applied, at least 24% of the unpolarized light incident on the light guide (5) that can be switched parallel to the first preferred direction or the second preferred direction is transmitted, while at least 85% of the unpolarized light incident on the light guide (5) that can be switched at an angle of 30 degrees or more with respect to the corresponding preferred direction is absorbed. In the second operation mode B2, when the polarization filter (P) is present, the transition dipole moment thereof and the transition dipole moment of the switchable optical element (1, 2) closest to the polarization filter (P) are oriented perpendicular to each other, and the transition dipole moments of both optical elements (1, 2) are oriented parallel to each other. A switchable optical filter (5). [Configuration 5] The switchable optical filter (5) according to Configuration 1 or 3, characterized in that at least one polarization compensation layer is arranged in front of and / or behind the liquid crystal layer (3). [Configuration 6] The switchable optical filter (5) according to any one of Configurations 1 to 5, characterized in that the preferred directions each form an angle of 0 to 45 degrees with respect to the surface normal of the first layer (S1). [Configuration 7] The switchable optical filter (5) according to any one of Configurations 1 to 6, characterized in that the switchable optical filter (5) is divided into a plurality of separately switchable segments, and local switching between possible operating states is enabled. [Configuration 8] The switchable optical filter (5) according to any one of Configurations 1 to 7, characterized in that each layer (S1, S2,...) of the first optical element (1) and / or the second optical element (2) if present is configured aperiodically in its structure. [Configuration 9] A screen including the switchable optical filter (5) according to any one of Configurations 1 to 8 and an image display unit provided behind or in front of the switchable optical filter (5) as viewed by an observer. [Configuration 10] An optical element, - comprising a first layer (S1), or a first layer (S1) and a plurality of other layers (S2,...), - each layer (S1, S2,...) comprising a material having a large number of transition dipole moments that absorb light, - each transition dipole moment being oriented parallel to or fluctuating around a selectable first preferred direction with a tolerance of at most 10 degrees, at least in a first state, - As a result, the light incident on the optical element is an optical element that transmits or at least partially absorbs according to the incident direction with respect to the layer (S1, S2,...) and its polarization state. [Configuration 11] The switchable optical filter (5) according to Configuration 10, wherein the preferred directions each form an angle of 0 to 45 degrees with respect to the surface normal of the first layer (S1). [Configuration 12] The switchable optical filter (5) according to Configuration 10 or 11, wherein each layer (S1, S2,...) is configured aperiodically in its structure. [Configuration 13] The optical element according to any one of Configurations 10 to 12, wherein each transition dipole moment is oriented within a tolerance of up to 10 degrees around the respective preferred direction in the respective preferred direction. [Configuration 14] The optical element according to any one of Configurations 10 to 13, wherein at least two such preferred directions differ by 10 degrees or more within a selectable plane. [Configuration 15] The optical element according to any one of Configurations 10 to 14, wherein the transition dipole moments of each layer (S1, S2,...) can be changed between their orientation and / or magnitude between a first state and at least a second state, so that each layer can be in any of at least two different states. [Configuration 16] The optical element according to Configuration 15, characterized in that it is divided into a plurality of segments that can be switched separately between a first state and at least a second state. [Configuration 17] The optical element according to any one of Configurations 10 to 16, wherein the respective preferred directions of the transition dipole moments are selectable according to their positions in each layer (S1, S2,...). [Configuration 18] Each layer (S1, S2,...) is divided into various regions (A1, A2,...) along a selectable reference line on each layer (S1, S2,...), and a unique region preferred direction is selectable for each region (A1, A2,...). This region preferred direction corresponds to all the transition dipole moments of the corresponding layer (S1, S2,...) within the region (A1, A2,...), and all the region preferred directions are different from each other one by one and are oriented towards the viewer (3) with a tolerance of up to ±10 degrees. The optical element according to any one of Configurations 10 to 17. [Configuration 19] The optical element according to any one of Configurations 10 to 18, characterized in that the material contains at least one type of dye, preferably a dichroic dye mixture. [Configuration 20] The optical element according to any one of Configurations 10 to 19, characterized in that the material contains liquid crystal. [Configuration 21] The optical element according to any one of Configurations 10 to 20, characterized in that it is formed as a laminate of layers of a polymer film polarizer. [Configuration 22] A lighting device for a screen that can be operated in at least two operating modes, an operating mode B1 for a free viewing mode and an operating mode B2 for a restricted viewing mode, - A planar extended backlight that emits light including the optical element according to any one of Configurations 11 to 22, - A plate-shaped light guide having output elements on at least one large surface and / or within its volume, in front of the backlight in the viewing direction, the light guide being at least 40% transparent to the light emitted from the backlight, - A light source arranged laterally on at least one narrow side of the light guide, - A linear polarizing filter arranged in front of the backlight or in front of the light guide in the viewing direction, and the light emitted from the backlight and passing through the polarizing filter has its propagation direction restricted by this linear polarizing filter, - A lighting device characterized in that in operating mode B2 the backlight is on and the light source is off, and in operating mode B1 at least the light source is on. [Configuration 23] The lighting device according to Configuration 22, characterized in that the light guide is at least 70% transparent to the light emitted from the backlight. [Configuration 24] A screen that can be operated in at least two operating modes, an operating mode B1 for a free viewing mode and an operating mode B2 for a restricted viewing mode - A planar extended backlight that emits light including the optical element according to any one of Configurations 11 to 22, - A plate-shaped light guide having output elements on at least one large surface and / or within its volume, in front of the backlight in the viewing direction, the light guide being at least 40% transparent to the light emitted from the backlight, - A light source arranged laterally on at least one narrow side of the light guide, - A linear polarizing filter arranged in front of the backlight or in front of the light guide in the viewing direction, and the light emitted from the backlight and passing through the polarizing filter has its propagation direction restricted by this linear polarizing filter, - A transmissive image display unit disposed in front of the light guide body in the viewing direction, and a linear polarizing filter is disposed in the image display unit. - A screen characterized in that the backlight is on and the light source is off in operation mode B2, and at least the light source is on in operation mode B1. [Configuration 25] The screen according to Configuration 24, wherein the light guide body is at least 70% transparent to the light emitted from the backlight. [Configuration 26] The display screen according to Configuration 24 or 25, wherein the linear polarizing filter is disposed in the transmissive image display unit or is a part thereof.

Explanation of Symbols

[0157] 1 First optical element 2 Second optical element 3 Liquid crystal layer 4 Alignment layer 5 Switchable optical filter 6 Viewer 7 Optically anisotropic layer A1...A5 Regions E1, E2 Electrodes E2 Second electric field P Polarizing filter S Transparent substrate S1...S3 layers

Claims

1. A switchable optical filter (5), a first optical element (1) comprising a first layer (S1), or a first layer (S1) and several further layers (S2, ...), Each layer (S1, S2, ...) comprises a material having multiple transition dipole moments that absorbs light; the material comprises a dye mixture comprising dye molecules, each dye molecule being associated with a transition dipole moment; each of said layers (S1, S2, ...) is aperiodically structured in its structure and has a thickness ranging from 0.2 μm to 50 μm; each transition dipole moment, at least in a first state, is oriented parallel to or fluctuates about a selectable first preferred direction for said first optical element (1) with a tolerance of up to 10 degrees, so that light incident on the first optical element (1) is transmitted or at least partially absorbed depending on its direction of incidence and its polarization state relative to the layers (S1, S2, ...), the transition dipole moments of each of the layers (S1, S2, ...) can change their orientation and / or magnitude between the first state and at least a second state to place each layer (S1, S2, ...) in one of at least two different states; A first optical element (1); a polarizing filter (P) arranged in front of or behind said first optical element (1), means for selectively generating a first electric field (EF1) or a second electric field (EF2), the first state being generated by applying the first electric field (EF1) and the second state being generated by applying the second electric field (EF2) to the first optical element (1); and, as a result, in a first operating mode B1 having a first sub-mode B1H and a second sub-mode B1V, in which the first electric field (EF1) is applied such that the transition dipole moments of the layers (S1, S2, ...) of the first optical element (1) are oriented along the first preferred direction, at least 24% of unpolarized light incident on the switchable optical filter (5) parallel to the first preferred direction is transmitted, while at least 85% of unpolarized light incident on the switchable optical filter (5) at an angle of 30 degrees or more to the first preferred direction is absorbed, which absorption takes place only in a first direction in the first sub-mode B1H and only in a second direction perpendicular to the first direction in the second sub-mode B1V, - in a second operating mode B3 in which the second electric field (EF2) is applied so that the transition dipole moments of the layers (S1, S2, ...) of the first optical element (1) are oriented parallel to the surface of the polarizing filter (P) and perpendicular to the transmission direction of the polarizing filter (P), a switchable optical filter (5) in which at least 24% of unpolarized light incident on the switchable optical filter (5) at any angle relative to the first preferred direction is transmitted.

2. A switchable optical filter (5), - both a first optical element (1) and a second optical element (2) each comprising a first layer (S1), or a first layer (S1) and a number of further layers (S2, ...), Each layer (S1, S2, ...) comprises a material having multiple transition dipole moments that absorbs light; the material comprises a dye mixture comprising dye molecules, each dye molecule being associated with a transition dipole moment; each of said layers (S1, S2, ...) is aperiodically structured in its structure and has a thickness ranging from 0.2 μm to 50 μm; each transition dipole moment, at least in a first state, is oriented parallel to or fluctuates around a selectable first preferred direction for the first optical element (1) and a selectable second preferred direction for the second optical element (2) with a tolerance of up to 10 degrees, so that light incident on the first optical element (1) or the second optical element (2) is transmitted or at least partially absorbed depending on the direction of incidence and its polarization state with respect to the layers (S1, S2, ...), the transition dipole moments of each of the layers (S1, S2, ...) can change their orientation and / or magnitude between the first state and at least a second state to place each layer (S1, S2, ...) in one of at least two different states; A first optical element (1) and a second optical element (2); means for selectively generating a first electric field (EF1) or a second electric field (EF2), the first state being generated by applying the first electric field (EF1) and the second state being generated by applying the second electric field (EF2) for each of the optical elements (1, 2); an optically anisotropic layer (7) arranged between said optical elements (1, 2), which rotates by 90° the polarization direction of light passing through said optically anisotropic layer (7); having optionally with a polarizing filter (P) arranged above or below both optical elements (1, 2), or without a polarizing filter (P), so that in a first operating mode B1, in which the first electric field (EF1) is applied, at least 24% of unpolarized light incident on the switchable optical filter (5) at any angle relative to the switchable optical filter (5) is transmitted, and in said first operating mode B1 the transition dipole moments of both optical elements (1, 2) are oriented perpendicular to each other and, if a polarizing filter (P) is present, the polarizing filter transition dipole element of the polarizing filter (P) is oriented parallel to the transition dipole moment of the switchable optical element (1, 2) closest to the polarizing filter (P), a switchable optical filter (5) in which, in a second operating mode B2 in which the second electric field (EF2) is applied, at least 24% of unpolarized light incident on the switchable light guide (5) parallel to the first preferred direction or the second preferred direction is transmitted, while at least 85% of unpolarized light incident on the switchable light guide (5) at an angle of 30 degrees or more to the corresponding preferred direction is absorbed, and in the second operating mode B2, if a polarizing filter (P) is present, its transition dipole moment and the transition dipole moment of the switchable optical element (1, 2) closest to said polarizing filter (P) are oriented perpendicular to each other, and the transition dipole moments of both optical elements (1, 2) are respectively oriented parallel to each other.

3. 3. A switchable light filter (5) according to claim 2, characterised in that at least one polarization compensation layer is arranged in front of and / or behind the optically anisotropic layer (7).

4. A switchable optical filter (5) according to any one of claims 1 to 3, characterised in that the preferred directions each make an angle between 0 and 45 degrees with respect to the surface normal of the first layer (S1).

5. 5. A switchable optical filter (5) according to any one of claims 1 to 4, characterized in that the switchable optical filter (5) is divided into a plurality of separately switchable segments, each allowing local switching between possible operating states.

6. 6. A switchable optical filter (5) according to any one of claims 1 to 5, characterized in that each of the layers (S1, S2, ...) of the first optical element (1) and / or the second optical element (2), if present, is configured aperiodically.

7. A screen comprising a switchable light filter (5) according to any one of claims 1 to 6 and an image display unit arranged behind or in front of the switchable light filter (5) from the point of view of a viewer.

8. An optical element, - comprising a first layer (S1), or a first layer (S1) and several further layers (S2, ...), each layer (S1, S2, ...) comprises a material with multiple transition dipole moments that absorbs light; the material comprises a dye mixture comprising dye molecules, each dye molecule being associated with a transition dipole moment; each transition dipole moment is oriented parallel to or fluctuates about a selectable preferred direction with a maximum tolerance of 10 degrees; as a result, light incident on the optical element is either transmitted or at least partially absorbed depending on the direction of incidence relative to the layers (S1, S2, ...), the preferred direction is at an angle between 0 degrees and 45 degrees with respect to the surface normal of the first layer (S1); An optical element, characterized in that each of said layers (S1, S2, ...) is aperiodically arranged in its structure and has a thickness ranging from 0.2 μm to 50 μm.

9. The optical element of claim 8, characterized in that it is formed as a laminate of layers of polymer film polarizers.

10. 10. An optical element according to claim 8 or 9, characterized in that the preferred direction of each of the transition dipole moments is selectable depending on its position in each layer (S1, S2, ...).

11. 11. An optical element according to claim 8, characterized in that each layer (S1, S2, ...) is divided into various regions (A1, A2, ...) along selectable reference lines on the respective layer (S1, S2, ...), and a specific region preferred direction is selectable for each region (A1, A2, ...), which region preferred direction applies to all the transition dipole moments of the corresponding layers (S1, S2, ...) in the region (A1, A2, ...), and all region preferred directions are pairwise different from each other and point towards the viewer (3) with a tolerance of maximum ±10 degrees.

12. 1. A lighting device for a screen which can be operated in at least two operating modes: an operating mode B1 for a free viewing mode and an operating mode B2 for a restricted viewing mode, - a planar extended backlight comprising an optical element according to any one of claims 8 to 11; a plate-like light guide in front of the backlight in the viewing direction and having output elements on at least one major surface and / or within its volume, the light guide being at least 40% transparent to the light leaving the backlight; a light source arranged laterally on at least one narrow side of said light guide; a linear polarising filter arranged in front of the backlight or in front of the light guide in the viewing direction, by which light leaving the backlight and passing through the polarising filter is restricted in its direction of propagation; an illumination device, characterized in that in operating mode B2, said backlight is on and said light source is off, and in operating mode B1, at least said light source is on.

13. A screen that can be operated in at least two operating modes: an operating mode B1 for a free viewing mode and an operating mode B2 for a restricted viewing mode, - a planar extended backlight emitting light comprising an optical element according to any one of claims 8 to 11; a plate-like light guide in front of the backlight in the viewing direction and having output elements on at least one major surface and / or within its volume, the light guide being at least 40% transparent to the light leaving the backlight; a light source arranged laterally on at least one narrow side of said light guide; a linear polarizing filter arranged in front of the backlight or in front of the light guide in the viewing direction, by which the light leaving the backlight and passing through the polarizing filter is restricted in its direction of propagation; a transmissive image display arranged in front of the light guide in a viewing direction, the transmissive image display having the linear polarizing filter arranged therein or being part of the transmissive image display, A screen characterised in that in operating mode B2 said backlight is on and said light source is off, and in operating mode B1 at least said light source is on.

14. 14. The screen according to claim 13, wherein the linear polarizing filter is disposed within the transmissive image display device.

Images