Filters, lighting devices and filter screens

Abstract

An optical filter (5) according to a first aspect of the present invention includes a first optical element (1) and a second optical element (2), each of which comprises a plurality of optical absorption transition dipole moments, a majority of which are arranged, at least in a first state, to be parallel to or vary 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 20°, such 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 incident direction (4) and its polarization state relative to the corresponding optical element (1, 2). The retardation layer (7) is in the form of a C-plate or an A-plate and is arranged between the first optical element (1) and the second optical element (2), such that at least 85% of linearly polarized or elliptically polarized light incident on the filter (5) at an angle of at least 35° to the first preferred direction or the second preferred direction is absorbed, where the angle between the electric field of the linearly polarized light or the major semi-axis (6) of the elliptical polarization when projected onto the surface of the filter (5) and the direction of incidence (4) is less than 20°. The present invention further comprises a second embodiment comprising a biaxial optical filter (5a) and an arrangement method for applying the optical filter (5, 5a) according to the present invention to a lighting device and a screen.

Description

[Technical Field]

[0001] In recent years, great progress has been made in expanding the viewing angle of LCDs. However, in some cases, the extremely large viewing area of ​​a screen can often be a disadvantage. More and more information (e.g., banking data or other personal and sensitive data) can be obtained from mobile devices such as laptops and tablet computers. Therefore, it is necessary to control who can view this sensitive data. To share the information on the screen with others, a wide viewing angle can be selected (e.g., to view travel photos or advertisements). Alternatively, to keep the information on the screen private, a narrower viewing angle (in privacy mode) is required.

[0002] The same problem exists in vehicle construction: when the engine is on, the driver cannot pay attention to the image content, such as entertainment programs, and passengers want to watch such content while driving. Therefore, a screen that can switch between corresponding display modes is required. [Background technology]

[0003] Microlouvered film has been used in mobile display devices to provide visual data protection. However, the film is not controllable or switchable, and can only be attached and removed manually. When not needed, the film must be peeled off separately to reveal the image. Another major drawback of using such louvered film is that it suffers from a certain amount of light loss.

[0004] US6765550 B2 describes such a microlouver anti-peeping barrier, the drawback of which is that the filters need to be mechanically removed and attached and there is a loss of light in the protection mode.

[0005] US5993940A describes the use of a film, on the surface of which small prism strips are uniformly arranged to achieve a privacy mode, but the development and production costs are considerable.

[0006] In WO2012 / 033583 A1, switching between free mode and limited mode is performed by controlling the liquid crystal between so-called "color" layers, which leads to light loss and significantly increases costs.

[0007] US2012 / 0235891 A1 describes a highly complex screen backlight. As shown in Figures 1 and 15 of the document, it uses multiple light guides as well as other complex optical elements, such as microlens elements 40 and prism structures 50, to convert rear-illumination light rays into front-illumination light rays. This is expensive, complex, and causes light loss. According to a variation shown in Figure 17 of US2012 / 0235891 A1, two light sources 4R and 18 both generate light rays with narrow emission visual angles, and the light rays of the rear light source 18 are first converted into light rays with a wide emission visual angle in a complex manner. As mentioned above, such complex conversion significantly reduces brightness.

[0008] JP2007-155783 A uses a special optical surface 19 that is complex to calculate and manufacture in order to deflect light rays into different narrow or wide areas depending on the light incident angle. This structure is similar to a Fresnel lens. In addition, interference edges may deflect light rays in undesirable directions. Therefore, it is unclear whether a meaningful light distribution can be achieved.

[0009] US2013 / 0308185 A1 describes a special stepped light guide that can be combined with a transmissive image display device (e.g., a liquid crystal display) to create a screen that can be switched between free-viewing mode and limited-viewing mode. Its drawbacks include the fact that the limited visual effect can only be used on the left / right side or the top / bottom side, and cannot be used on the left / right side / top / bottom side at the same time, which is necessary for certain payment processes. Furthermore, even in limited-viewing mode, residual light rays can be seen from blocked angles of view.

[0010] WO2015 / 121398 A1 describes a screen with two operating modes, where scattering particles present in each light guide essentially switch between operating modes. However, polymeric scattering particles generally have the disadvantage of emitting light from two large surfaces, resulting in approximately half of the useful light being misdirected, i.e., toward the backlight, and these light rays are not recycled to a sufficient extent due to the structure. In addition, in some cases, the polymeric scattering particles in the light guide, especially at high concentrations, can cause a scattering effect, reducing the anti-peeping effect in the protective mode.

[0011] The core idea of ​​electric birefringence technology is to use switchable liquid crystals in an additional liquid crystal panel to "filter" light exiting the imaging layer at a specific angle. However, this technology has several drawbacks, including excessive energy consumption and high cost, as well as difficulty in adjusting the optimal viewing angle (i.e., the optimal viewing position), which is usually fixed at approximately ±40°. In addition, the light absorption ability of the liquid crystal structure is insufficient, and the light intensity is not attenuated sufficiently for viewing angles greater than the optimal viewing angle, so the light intensity can only reach 3% of the maximum light intensity even at viewing angles greater than ±40°.

[0012] Such methods and apparatus typically suffer from the following drawbacks: they significantly reduce the brightness of the base screen, and / or they require complex and expensive optics for mode switching, and / or they reduce the resolution in free-viewing and open modes, and / or they introduce visual artifacts on very high-resolution displays. Summary of the Invention

[0013] The objective of the present invention is to describe an optical filter having an optical element that transmits, partially absorbs, or fully absorbs light incident on the optical element depending on its direction of incidence and polarization characteristics (but not its position). This optical element filter allows light transmission to be switched depending on the angle (preferably perpendicular to a seated or standing observer), and preferably allows switching between at least two operating states. In particular, it allows switching transmission behavior for specific directions. In the prior art, such optical elements achieve directional selectivity through polarization characteristics, and when the electric field absorption is perpendicular to the film surface, their transmission diagram (e.g., represented by false color in a polar coordinate system) exhibits an undesirable hourglass shape. Typically, the absorption of such optical elements does not significantly enhance the anti-spy effect. Therefore, without further improvements, this principle of anti-spying is limited. Due to the hourglass shape, when transmittance is used as the evaluation criterion for anti-spying, for light linearly polarized along the horizontal direction, the transmittance at vertical viewing angles greater than 5° is always higher than the transmittance at vertical viewing angles less than 5°, and this usually applies to the entire or at least most horizontal angle range. Therefore, an object of the present invention is to reduce the transmittance when the vertical angle of view is greater than 5° (i.e., improve the anti-peeping capability) while maintaining the transmittance when the vertical angle of view is less than 5°, and to achieve this effect even at different horizontal angles. The concept of "vertical" here refers, as an example, to the direction in which an observer (whether sitting or standing) looks at the filter. For reference, the line connecting the observer's eyes is taken as the horizontal direction, and the direction perpendicular to this direction is taken as the vertical direction. Here, "vertical" is defined as vertical when, as an example, the observer is standing or sitting and facing the optical filter, and the line connecting the observer's eyes is taken as the horizontal direction and the vertical direction.

[0014] An optical filter according to a first embodiment of the present invention includes a first optical element and a second optical element, each of which has a plurality of absorption transition dipole moments. The two optical elements are stacked in a direction parallel to the incident light so that light passes through them in sequence. In a plate-like optical element having two large surfaces and connected by a narrow edge, light passes through the two stacked large surfaces in sequence. The stacked arrangement should not be understood as meaning that the two optical elements are directly adjacent to each other; in some embodiments of the present invention, at least one other element is present between the optical elements.

[0015] In at least one first state, the majority of the transition dipole moments are parallel to the first preferred direction of the first optical element and the second preferred direction of the second optical element, with a tolerance of up to 20° (preferably up to 10°), or fluctuate or change around these directions. In the present invention, the term "at least one first state" encompasses multiple possibilities. In one aspect, only one state may exist as a permanent configuration. In another aspect, multiple states may exist. In this case, the orientation of the transition dipole moments is variable, as achieved, for example, by a so-called host-guest liquid crystal cell. Light incident on the first or second optical element is transmitted or partially absorbed depending on the incident direction and polarization state relative to the respective optical element.

[0016] A retardation layer is provided between the first and second optical elements. This retardation layer is configured as a C-plate or A-plate to generate a retardation greater than λ / 4, e.g., a λ / 2 retardation, for a predetermined wavelength λ. In all cases, the retardation must be greater than λ / 4. The predetermined wavelength may be a so-called "design wavelength," and the filter is optimized using a corresponding design program (e.g., LCD Master, Techwiz, and / or algorithms known in the art, e.g., A. Lien, "Extended Jones matrix representation for the twisted nematic liquid-crystal display at oblique incidence," Appl. Phys. Lett. 1990, Dec. 24; 57(26):2767-2769, https: / / doi.org / 10.1063 / 1.103781). Typically, a "green" wavelength, such as λ=550 nm, is selected, but in principle, any wavelength in the visible light range can be used.

[0017] Thus, if the angle between the electric field of linearly polarized light or the semimajor axis of elliptically polarized light (both projected onto the surface of the filter) and the direction of incidence is less than 20°, then linearly or elliptically polarized light (especially strongly elliptically polarized light) incident on the filter at an angle of at least 35° to the first or second preferred direction will be absorbed by at least 85%.

[0018] Here, strong elliptically polarized light refers to a semiaxial length ratio of 1: 4 or more, and more preferably 1: 10 or more. For example, it is conceivable that only linearly polarized light or strong elliptically polarized light is incident on the filter.

[0019] The mechanism by which the combination of the first optical element, the retardation layer (A-plate or C-plate), and the second optical element improves anti-spying can be conceptually explained as follows: For convenience of explanation, it is assumed that the absorption transition dipole moment is aligned perpendicular to the surface of the optical element. That is, the first and second preferred directions are the same because they are both perpendicular to the corresponding optical element. The first optical element primarily absorbs the electric field component of p-polarized light. When linearly polarized light is incident on the first optical element, it is most absorbed if it is polarized only in the plane of incidence. The larger the angle between the plane of incidence and the polarization direction (i.e., the larger the corresponding vertical viewing angle), the higher the transmittance. Therefore, the angle-dependent two-dimensional transmission diagram of the first optical element exhibits an hourglass shape. Next, a retardation layer (A-plate or C-plate) made of a uniaxial birefringent material is inserted after the first optical element so that its extraordinary axis is parallel or perpendicular. Since the light passing through the retarder is no longer polarized along only one of the two principal axes of the retarder, at least a portion of the s-polarized light passing through the retarder is converted to p-polarized light, which can then be absorbed by the subsequent second optical element. Therefore, the original hourglass shape is transformed into a rectangular shape, which can better restrict the field of view within the anti-peeping area without reducing brightness.

[0020] The first and second optical elements may have different layer thicknesses of the material having an optically absorbing transition dipole moment. To the extent technically feasible, the layer thicknesses may be the same or nearly the same. Typically, each optical element further comprises a transparent substrate (e.g., glass or polymer) on which the optically absorbing transition dipole moment material is disposed.

[0021] A transition dipole moment (also called a transition matrix element) is a quantum mechanical vector and a specific transition, i.e., a transition of a system from an initial state (generally the ground state) to a final state (generally an excited state), e.g., in an atom, molecule, or solid. It corresponds to the electric dipole moment associated with this transition. The direction of the vector defines the polarization (or polarization direction, synonymous here) of the transition, which in turn determines how the system interacts with electromagnetic waves of a given polarization and absorbs light of the corresponding polarization direction when transitioning from the ground state to the excited state. The magnitude of the vector corresponds to the strength of the interaction and the probability of the transition. The excited state relaxes through non-radiative processes.

[0022] The first or second preferred direction corresponds to the alignment direction of the transition dipole moment of the first or second optical element in a given light propagation direction, where the absorption is the same for any polarization direction of light.

[0023] Preferably, the first and second preferred directions may be the same, or may differ in their alignment directions by a few degrees (maximum 10 degrees), and may be specifically perpendicular to the respective optical elements. Depending on the application, the first and second preferred directions may differ by more than 10 degrees.

[0024] The filter may further include a polarizing filter positioned in front of or behind the first or second optical element in the incident direction. When the linear polarizing filter is positioned in front of the first or second optical element in the incident direction, the polarizing filter linearly polarizes the light incident on each optical element. Conversely, when the linear polarizing filter is positioned behind the first or second optical element in the incident direction, it is used to remove unwanted polarization components from the light output from the first or second optical element. It is also possible to use a λ / 4 retardation layer. For example, if the incident light is circularly polarized, this layer converts the circularly polarized light into approximately linearly polarized light. The corresponding design wavelength λ can be, for example, 550 nm or 580 nm. Other wavelength values ​​are clearly possible.

[0025] The optical filter may further include a device for selectively generating a first electric field EF1 or a second electric field EF2 so as to substantially realize two different operation modes. A liquid crystal layer is provided in front of or behind the first optical element and / or the second optical element, and the first electric field EF1 or the second electric field EF2 acts on the liquid crystal layer, affecting the polarization state of light passing through the liquid crystal layer depending on the difference in the electric fields, thereby causing the transmission characteristics of the filter to differ between the first operation mode B1 (application of the first electric field EF1) and the second operation mode B2 (application of the second electric field EF2). If more electric fields can be generated, other operation modes can be realized.

[0026] In a preferred embodiment, when the second electric field EF2 is applied, the light transmitted through the liquid crystal layer remains substantially unchanged, and when the first electric field EF1 is applied, the incident light becomes circularly or elliptically polarized, or the polarization direction of the light is rotated by 90°.

[0027] The second electric field EF2 is for example 0 V / μm and the first electric field EF1 varies from 0.1 V / μm to 10 V / μm in a square wave of for example 1 kHz. This is also possible in other embodiments.

[0028] The object of the present invention can also be achieved by a second embodiment of the optical filter of the present invention. This optical filter includes a third optical element instead of the first and second optical elements described in the previous embodiment. This third optical element also includes a plurality of light-absorbing transition dipole moments. Similarly, the majority of the transition dipole moments, at least in a first state, are aligned parallel to or fluctuate around the third preferred direction of the third optical element with a tolerance of up to 20° (preferably up to 10°). In the present invention, the characteristic "at least a first state" includes multiple possibilities. In one aspect, only one state may exist as a permanent configuration. In another aspect, the expression explicitly includes situations in which two or more states may exist. In this case, the transition dipole moments are variable, for example, realized by a host-guest liquid crystal cell, so that light incident on the third optical element is transmitted or at least partially absorbed depending on the incident direction and polarization state relative to the third optical element.

[0029] Since the third optical element is made of a biaxially birefringent material, according to the present invention, the complex refractive indices of the three principal axes x, y, and z within the third optical element are different from one another. Preferably, these three linearly independent and different principal axes x, y, and z are located in a Cartesian coordinate system. Thus, when the angle between the electric field of linearly polarized light or the semimajor axis of elliptically polarized light and the direction of incidence (both projected onto the surface of the filter) is less than 20°, linearly polarized light or elliptically polarized light (especially strongly elliptically polarized light) incident on the filter at an angle of at least 35° from the third preferred direction is absorbed by at least 85%. Similarly, strongly elliptically polarized light refers to a semimajor axis ratio of at least 1:4, and more preferably at least 1:10 or more.

[0030] Furthermore, in the second embodiment of the present invention, the filter may include a linear polarizing filter located in front of or behind the third optical element in the incident direction. When the linear polarizing filter is located in front of the third optical element in the incident direction, it ensures linear polarization of the light incident on the third optical element. Conversely, when the linear polarizing filter is located behind the third optical element in the incident direction, it is used to remove unnecessary polarization components from the light output from the third optical element. It is also possible to use a λ / 4 retardation layer. For example, if the incident light is circularly polarized light with a wavelength λ, this layer converts the circularly polarized light into approximately linearly polarized light.

[0031] As mentioned above, the three principal axes x, y, and z are different from one another, and specifically, they are expressed as being linearly independent. The third optical element has a layer thickness d, more precisely, the thickness of the layer having the extinction transition dipole moment. In a first preferred variant of the second embodiment, the biaxially birefringent material of the third optical element has a complex refractive index n along the principal axes. x =n2-i×k2, n y =n1-i×k2, n z =n1-i×k1, and their complex refractive indices satisfy |n1-n2|×d≧λ / 4(k1 / k2>10), where i is the imaginary part, n1, n2, and n3 are the real refractive indices, and k1, k2, and k3 are the absorption coefficients.

[0032] Refractive index n x , n y , n z The coordinate system direction is correlated only with the arrangement direction of the main axes, and is tilted and rotated relative to the screen coordinate system.

[0033] In a second preferred variant of the second embodiment, the biaxially birefringent material of the third optical element has a complex refractive index n along the principal axis. x =n2-i×k2, n y =-i×k2,n z = n3-i × k1, |n1-n2| × d ≥ λ / 4, k1 / k2 > 10, |n2-n3| ≤ |n1-n2| / 2.

[0034] The mechanism of action of the second embodiment of the present invention will now be described.

[0035] The third optical element made of a biaxially birefringent material in the second embodiment, or a third optical element including such a material, can conceptually be considered as a laminated system in which "transition dipole moment" layers and "A-type retarder" layers are alternately stacked. The transition dipole moment layer absorbs p-polarized light. Preferably, when the third preferred direction is perpendicular to the large surface of the optical element, optimal anti-spying, i.e., horizontal transmission restriction for the optimal angle, can be achieved at a horizontal viewing angle where the vertical viewing angle component is 0°. However, as the vertical viewing angle deviates from 0°, the anti-spying effect at the same horizontal viewing angle decreases. This is related to the undesirable hourglass-shaped transmission diagram in the prior art mentioned in the description of the purpose of the present invention. As mentioned above, conceptually, the transition dipole moment layer absorbs p-polarized light, so the transmitted light is polarized. Conceptually, the A-type retarder converts linearly polarized light into elliptically polarized light, which can then be absorbed (at least in part) by the next (conceptually) layer, the transition dipole moment layer, improving the angular transmission limit. Conceptually, due to the alternating structure of multiple "transition dipole moment" layers and "A-type retarder" layers, embodiments of the present invention significantly improve the angular transmission limit compared to the prior art.

[0036] Alternatively, the fabrication of the biaxial third optical element can be similar to known methods for fabricating biaxial films, for example, by polymerizing liquid crystal mesogens and then doping them with dichroic dye molecules or mixtures thereof.

[0037] An exemplary method for producing a first, second, or third optical element based on the host-guest effect includes the following steps based on a mixture of dichroic dyes or a combination of a mixture of dichroic dyes and a liquid crystal mixture or compound (see, for example, US9481658 B2 or WO2021 / 177308 A1, paragraphs 37 et seq.): A thin film is applied to a low-birefringence or non-birefringence substrate, and the thin film determines a molecular alignment direction relative to the surface, typically parallel or perpendicular to the surface. For this purpose, a polymer is typically used, with polyvinyl alcohol (PVAL / PVOH) or polyimide (PI) being preferred. Preferably, the surface may be optically or mechanically treated to improve the quality of subsequent molecular alignment. Next, a mixture of a dichroic dye and a liquid crystal compound or polymer is applied to the substrate. Finally, localized light irradiation is used to crosslink the side chains, aligning them along the surface and creating a birefringence effect.

[0038] Alternatively, a variant of the second manufacturing method may use a thermotropic liquid crystal dichroic dye, for example, as described in JP2011-237513A, which involves preparing the corresponding dye, adding a polar group, coating the dye mixture, and finally photo-aligning and curing the dye mixture with polarized light.

[0039] For example, the following materials can be used in different manufacturing processes (this list is not exhaustive): As a low or no birefringence polymer substrate, triacetyl cellulose (TAC) is preferred; The dichroic material or mixture includes, but is not limited to, dichroic dyes (preferably azo dyes) or dichroic metal nanoparticles (preferably gold, silver, copper and aluminum), typically a single dye or a mixture of up to three different dyes, which provide absorption in a major part of the emission spectrum; As the polymer used for the surface treatment by arranging the dye or liquid crystal substance, polyvinyl alcohol and polyimide are preferred; For thermotropic liquid crystal compounds or polymers, see, for example, JP2011-237513A; The chemical cross-linking group (i.e., cross-linking group) bonded to the thermotropic liquid crystal compound or polymer includes, but is not limited to, a methacryl group, an epoxy group, an oxetanyl group, and a styryl group (preferably a methacryl group), or may be a polymerizable liquid crystal compound, such as those described in JP6268730 B2; Polymerizable liquid crystal dichroic dyes include, but are not limited to, azo dyes.

[0040] The at least one dye is composed of dye molecules, and preferably each dye molecule is associated with a transition dipole moment or transition dipole moment, i.e., each dye molecule corresponds to a transition dipole moment or transition dipole moment. The mass fraction of the dye in the material of each optical element is typically 0.01%-10%, preferably 0.1%-5%. In special cases, the concentration of the liquid crystal dichroic dye can reach 95%. Intermediate values ​​within the above range are also possible. The thickness of each layer is preferably 0.2 μm to 50 μm, inclusive, and more preferably 0.5 μm to 20 μm, inclusive. The dyes or dye mixtures in different layers within the optical element can be different, but do not necessarily have to be.

[0041] In accordance with both embodiments of the optical filter of the present invention, it is preferred that the first preferred direction, the second preferred direction or the third preferred direction forms an angle of 0°-45° with respect to the surface normal of the optical element, including all boundary values.

[0042] In addition, in the present invention, the first preferred direction (and, if present, the second or third preferred direction) may vary on the surface of each optical element. According to the present invention, the preferred direction of each optical element is determined to be the weighted average of all values. Preferably, the preferred direction of each of the multiple transition dipole moments can be selected depending on its position on the corresponding optical element.

[0043] In another preferred embodiment of the first, second or third optical element, the optical element is divided into different regions along selectable reference lines, each region having its own selectable preferred direction that applies to all transition dipole moments within the region, with every region having two different preferred directions and a maximum tolerance of ±10° in the observer direction. Thus, within a suitable region, all transition dipole moments are aligned parallel to the preferred direction of that region with a maximum tolerance of ±10°. This allows the observer to perceive the filtered screen as having a uniform illumination effect in limited vision mode.

[0044] In a second embodiment, the optical filter may further include the following devices and liquid crystal layers: a device for selectively generating the first electric field EF1 or the second electric field EF2; and A liquid crystal layer disposed in front of or behind a third optical element, wherein the first electric field EF1 or the second electric field EF2 acts on the liquid crystal layer, affecting the polarization state of light passing through depending on the difference in the electric field, and causing the transmission characteristics of the filter to differ between a first operating mode B1 (application of the first electric field EF1) and a second operating mode B2 (application of the second electric field EF2). Similarly, two or more different electric fields (corresponding to more possible operating modes) can be generated, but only one of the electric fields can be applied simultaneously.

[0045] In the two embodiments of the optical filter of the present invention, the switchable liquid crystal layer is in a first switching state, i.e., when a first electric field EF1 is applied, the incident light is transmitted almost unchanged; in a second switching state, i.e., when a second electric field EF2 is applied, the light is circularly or elliptically polarized, or the polarization direction of the light is rotated by 90°.

[0046] The term "substantially" means that the orientation of the liquid crystal molecules at the interface is determined by the electric field and the surface-induced force, so any disruption of the orientation of the liquid crystal molecules will result in a change in the polarization state.

[0047] The application of the light filter of the present invention to a lighting device for a screen or on (or inside) a screen is of particular significance. Therefore, the present invention also includes a lighting device for a screen that can operate in at least two operating modes (free-viewing mode B1 and limited-viewing mode B2), in which light is emitted within a limited angle range in the limited-viewing mode B2, as opposed to the free-viewing mode. This lighting device: a flat extended backlight for emitting light, the flat extended backlight including the optical filter according to the first embodiment or the second embodiment; a light guide plate arranged in front of the backlight along the viewing direction and having at least one large surface and / or coupling elements within its volume; a light source disposed laterally on at least one narrow surface of said light guide plate; a linear polarizing filter that is arranged in front of the backlight (8) or the light guide plate along the observation direction of the observer, and that limits the direction of travel of light that is emitted from the backlight and transmitted through the optical filter and the linear polarizing filter; Here, in the restricted viewing mode B2, the backlight is turned on and the light source is turned off, and in the free viewing mode, at least the light source is turned on, that is, only the light source is turned on, or the light source and backlight are turned on simultaneously.

[0048] When the optical filter of the lighting device described above includes a liquid crystal layer, the operating modes B1 and B2 depend on the state of the liquid crystal layer caused by the first electric field EF1 and the second electric field EF2, respectively. However, since the lighting device can be switched by simply switching between the backlight and the light source, the operating modes can be switched even if the filter does not include a liquid crystal layer.

[0049] The present invention also includes a screen that can operate in at least two operating modes (free-viewing mode B1 and limited-viewing mode B2), in which light is projected within a limited range of angles relative to the observer, as opposed to the free-viewing mode B1. a flat extended backlight for emitting light (optionally arranged to emit light directly), including an optical filter according to the first or second embodiment (both including the liquid crystal layer); a linear polarizing filter that is disposed in front of the backlight along the viewing direction of the screen viewer, and that restricts the direction of travel of light that is emitted from the backlight and transmitted through the optical filter and the linear polarizing filter; a transmissive display device (11) arranged in front of an optical filter along the viewing direction, in particular in front of a backlight and / or a polarizing filter; Here, in the limited vision mode B2, the second electric field (EF2) is applied, and in the free vision mode B1, the first electric field (EF1) is applied.

[0050] Preferably, the linear polarising filter is located in or on top of the transmissive display device or is part of the transmissive display device, and the optical filter may also be integrated into the transmissive display device, in particular sharing at least one common substrate with the transmissive display device.

[0051] Finally, the present invention also includes a screen operable in at least two operating modes (free-viewing mode B1 and limited-viewing mode B2), in which light is projected within a limited range of angles relative to the observer, as opposed to the free-viewing mode B1. A display device, for example an OLED panel, a micro LED panel, an LCD panel or any other type of screen; and an optical filter according to the first or second embodiment of the present invention (both of which include the liquid crystal layer described above), which is disposed in front of the display device along the viewing direction of the viewer; Here, in the limited vision mode B2, the second electric field (EF2) is applied, and in the free vision mode B1, the first electric field (EF1) is applied.

[0052] A special embodiment can be adopted for a screen having the transmissive display device (especially a screen having an LCD panel) that further includes a backlight: the backlight is designed to have a luminance distribution that is not substantially symmetric (e.g., symmetric about a vertical center line in the viewer's viewing angle) but is embodied as an asymmetric luminance distribution (e.g., in the horizontal direction). That is, it is preferable that the backlight has a luminance distribution that is asymmetric with respect to the horizontal direction of the viewer.

[0053] This is particularly advantageous for vehicle applications, since the backlight design significantly reduces the light emitted toward the passenger window by approximately 25° or more from the vertical bisector, for example, to less than 10% (preferably less than 2.5%) of the peak brightness, while maintaining high brightness for the light toward the driver. This also reduces ambient reflections from the passenger window and passenger side mirror. Nevertheless, because a filter is installed in front of the display device, the screen can be operated in a selectable mode, allowing only the passenger seat to view the image content (restricted viewing mode B2), for example, for playing videos, or allowing both the driver and passenger seat to view the image content (free viewing mode B1), for example, for displaying a navigation map.

[0054] For such a screen, an additional optical element (e.g., a first optical element, a second optical element, or a third optical element) may be provided in front of the transmissive display device along the viewing direction. If the transmissive display device is an LCD panel (e.g., capable of emitting vertically linearly polarized light suitable for polarized sunglasses), transmission upward and downward from the observer's viewpoint is limited, minimizing reflections on the windshield.

[0055] The optical filter according to the first or second embodiment of the present invention (both of which include the above-mentioned liquid crystal layer) can be arranged not only in front of the display device (particularly the LCD panel) but also behind the display device along the observation direction in a screen having the above-mentioned transmissive display device (particularly the LCD panel).

[0056] In a specific embodiment, the optical filter of the present invention can be retrofitted in front of a display device, such that a user's existing display device can be retrofitted to have at least two operating modes: a free-viewing mode B1 and a limited-viewing mode B2.

[0057] Such screens can be advantageously applied to mobile devices, land / air / water transport tools, payment terminals, or gate systems. By switching between different operating modes, it is possible not only to protect sensitive data (i.e., display visible content only to a single observer), but also to allow multiple observers to view image content simultaneously.

[0058] Essentially, the performance of the present invention can be maintained even when the parameters are varied within the specified ranges. It is understood that the features mentioned above and those described below may not only be used in the corresponding combinations indicated, but may also be used in other combinations or alone without departing from the scope of the present invention. [Brief explanation of the drawings]

[0059] The present invention will be described in detail below using embodiments in combination with the drawings. These drawings also disclose essential technical features of the present invention. It should be noted that these embodiments are merely illustrative and should not be construed as limiting the scope of protection. For example, a description of an embodiment including multiple elements or components does not necessarily mean that all elements or components are essential. Conversely, other embodiments may be realized using alternative elements or assemblies, a reduced number of elements, or additional elements. Unless otherwise specified, elements or assemblies in different embodiments can be combined with each other. Modifications and variations described for one embodiment are also applicable to other embodiments. To avoid redundancy, identical or corresponding elements in different drawings are designated by the same reference numerals, and redundant descriptions will be omitted. However, [Figure 1A]FIG. 1A is a principle schematic diagram of an exemplary two-dimensional angle-related diagram of transmittance of an optical filter in the prior art. [Figure 1B] FIG. 1B is a principle schematic diagram of an exemplary two-dimensional angle-related diagram of transmittance when an optical filter and a biaxial retardation plate are combined in the prior art. [Figure 2A] FIG. 2A is a schematic diagram of an optical filter structure in the first embodiment. [Figure 2B] FIG. 2B is a schematic diagram for explaining the semimajor axis of an elliptical light beam and its projection onto a plane in the incident direction. [Figure 3A] FIG. 3A is a schematic diagram of an extension structure for selectively varying filter transmission characteristics in an optical filter. [Figure 3B] FIG. 3B is a schematic diagram of an exemplary two-dimensional angular correlation diagram of the transmittance of the optical filter in the first embodiment. [Figure 4] FIG. 4 is a schematic diagram for explaining the principle of the complex refractive index of the biaxial third optical element. [Figure 5] FIG. 5 is a schematic diagram of an exemplary two-dimensional angle correlation diagram of the transmittance of the optical filter in the second embodiment under a first condition. [Figure 6] FIG. 6 is a schematic diagram of an exemplary two-dimensional angle correlation diagram of the transmittance of the optical filter in the second embodiment under the second condition. [Figure 7] FIG. 7 is a schematic diagram showing an example of an original angle correlation diagram of the horizontal transmittance of different optical filters when the vertical angle is 0°. [Figure 8] FIG. 8 is a schematic diagram of an exemplary original angle correlation diagram of horizontal transmittance for different optical filters when the vertical angle is 45°. [Figure 9] FIG. 9 is a structural schematic diagram of an illumination device using a screen that uses the optical filter according to the first or second embodiment. [Figure 10] FIG. 10 is a schematic diagram of a first structure of a screen using the optical filter according to the first or second embodiment, and the screen is operable in at least two operating modes (free-viewing mode B1 and limited-viewing mode B2). [Figure 11] FIG. 11 is a schematic diagram of a second structure of a screen using the optical filter according to the first or second embodiment, and the screen can operate in at least two operation modes (free-vision mode B1 and limited-vision mode B2). [Figure 12] FIG. 12 is a schematic diagram of a third structure of a screen using the optical filter according to the first or second embodiment, and the screen is operable in at least two operating modes (free-viewing mode B1 and limited-viewing mode B2). DETAILED DESCRIPTION OF THE INVENTION

[0060] The drawings are for illustrative purposes only and are not drawn to scale.

[0061] 1A, 1B, 3A, 5, and 6, the numerical values ​​attached to each curve indicate the normalized transmittance (based on "1") of the corresponding angle pair in the polar coordinate system. For example, the numerical values ​​"0, 12" in FIG. 3 indicate that the transmittance in the corresponding direction is 12%.

[0062] Optical filters known in the prior art achieve directional selectivity through polarization properties. When the electric field absorption direction is perpendicular to the film surface, the two-dimensional angular correlation diagram of transmittance in a polar coordinate system exhibits an undesirable hourglass shape. Figure 1A shows this diagram as a schematic diagram. Therefore, without further improvements, the anti-spying effect of this principle is limited. Due to this hourglass shape, transmittance is used as the evaluation criterion for anti-spying. For light linearly polarized along the horizontal direction, the transmittance at a vertical viewing angle greater than 5° is always higher than the transmittance at a vertical viewing angle less than 5°. This phenomenon can be seen in Figure 1A. The term "vertical" is an exemplary reference for the observer viewing the optical filter, and the observer may be standing or sitting. For reference, the line connecting the observer's eyes is defined as the horizontal direction, and the direction perpendicular to that direction is defined as the vertical direction.

[0063] In the prior art, such an optical filter was combined with a B-type retardation layer ("B plate"). Figure 1B is a schematic diagram of a two-dimensional angular correlation diagram of transmittance when an optical filter and a biaxial retardation plate are combined in the prior art. Although this solution has achieved some optimization, its effect still cannot meet the needs of all application scenarios.

[0064] Compared with the prior art, FIG. 2A is a schematic diagram showing an exemplary structure of the optical filter 5 in a first embodiment.

[0065] In a first embodiment, an exemplary optical filter 5 includes a first optical element 1 and a second optical element 2, each of which includes a plurality of light-absorbing transition dipole moments, and which are arranged in a stack (i.e., as stacked elements) with respect to an incident light direction 4. Here, the majority of the transition dipole moments, at least in a first state, are parallel to a first preferred direction of the first optical element and a second preferred direction of the second optical element, or fluctuate or change about these directions, with a tolerance of up to 20° (preferably up to 10°). In the present invention, the characteristic "at least a first state" encompasses multiple possibilities; in one aspect, only one state may exist as a permanent configuration. In another aspect, multiple states may exist. In this case, the orientation of the transition dipole moments is variable. 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 direction of incidence and its polarization state relative to each optical element 1, 2. A C-plate or A-plate retardation layer 7, such as a λ / 2 retardation layer, is provided between the first optical element 1 and the second optical element 2; in all cases, the retardation must be greater than λ / 4. This ensures that linearly or elliptically polarized light (especially strongly elliptically polarized light) incident on the optical filter 5 at an angle of at least 35° relative to the first or second preferred direction is absorbed by at least 85%. The angle between the electric field of the linearly polarized light or the semimajor axis 6 of the elliptical polarization and the direction of incidence 4 (both projected onto the surface 5 of the optical filter) is less than 20°.

[0066] For ease of understanding, Figure 2B shows a schematic diagram of the projection principle of the major semi-axis 6 and its incident direction 4 of an exemplary elliptical light onto the surface plane of the optical filter 5. The major semi-axis projection 6a and the incident direction projection 4a form an included angle α, which needs to be smaller than 20° to realize the working mechanism of the present invention.

[0067] The mechanism by which the combination of the first optical element, the retardation layer 7 (A-plate or C-plate), and the second optical element improves anti-spying can be conceptually explained as follows: For convenience of explanation, it is assumed that the absorption transition dipole moments are aligned perpendicular to the surface of the optical element, i.e., their respective preferred directions are perpendicular to the optical element (preferably). The first optical element primarily absorbs the electric field component of p-polarized light. When linearly polarized light is incident on the first optical element 1, it is best absorbed if it is polarized only in the plane of incidence. The larger the angle between the plane of incidence and the polarization direction (i.e., the larger the corresponding vertical viewing angle), the higher the transmittance. Therefore, the angle-dependent two-dimensional transmission diagram of the first optical element 1 exhibits an hourglass shape. Next, a retardation layer (A-plate or C-plate) made of a uniaxially birefringent material is inserted after the first optical element 1 so that its extraordinary axis is parallel or perpendicular. Since the light transmitted through the retardation layer 7 is no longer polarized along only one of the two principal axes of the retarder, at least a portion of the s-polarized light transmitted through the retardation layer 7 is converted to p-polarized light, which can be absorbed by the subsequent second optical element 2. Therefore, the original hourglass shape is converted to a rectangular shape, which can better limit the field of view within the anti-peeping area without reducing the brightness.

[0068] 3B is a schematic diagram of an exemplary two-dimensional angular correlation diagram of the transmittance of the optical filter in Example 1. Compared to the hourglass shape shown in FIGS. 1A and 1B, a narrower waist and reduced transmittance can be recognized.

[0069] The first and second optical elements may have the same first and second preferred directions, or may be slightly offset in their alignment directions (up to 10°), as is preferred in all of the examples shown in the figures.

[0070] 3A further illustrates a schematic diagram of an extended structure for selectively changing the filter transmission characteristics of an optical filter 5. The extended filter 5 further includes a double ITO layer having a device, such as a driving circuit, for selectively generating at least a first electric field EF1 or a second electric field EF2; and a liquid crystal layer 3 disposed at the front / rear end of the first optical element 1 and / or the second optical element 2 (not shown). Applying the first electric field EF1 or the second electric field EF2 to the liquid crystal layer 3 affects the polarization state of the transmitted light, so that the optical filter 5 exhibits different transmission characteristics between a first operating mode B1 in which the first electric field EF1 is applied and a second operating mode B2 in which the second electric field EF2 is applied.

[0071] Similarly, a retardation layer 7 (A-plate or C-plate) is also present here. As shown in Figure 3A, the filter 5 may further include a polarizing filter P located in front of or behind the first optical element 1 or the second optical element 2 in the direction of incidence.

[0072] In a preferred embodiment, when the second electric field EF2 is applied, the light transmitted through the liquid crystal layer 3 remains essentially unchanged, and when the first electric field EF1 is applied, the incident light becomes circularly or elliptically polarized, or the polarization direction of the light is rotated by 90°.

[0073] FIG. 4 also provides a schematic diagram illustrating the complex refractive index of a third optical element made of a biaxially birefringent material, particularly the optical filter 5a in the second embodiment. Exemplarily, the optical filter 5a includes a third optical element including a plurality of light-absorbing transition dipole moments, where the majority of the transition dipole moments, in at least a first state, are aligned parallel to or fluctuate around the third preferred direction of the third optical element with a tolerance of up to 20° (preferably up to 10°). In the present invention, the term "at least a first state" encompasses multiple possibilities, and in one aspect, only one state may exist as a permanent configuration. In another aspect, the term explicitly encompasses situations in which two or more states may exist. In this case, the transition dipole moments are variable, for example, realized by a host-guest liquid crystal cell, so that light incident on the third optical element is transmitted or at least partially absorbed depending on the incident direction and polarization state relative to the third optical element. As mentioned above, the third optical element is made of a biaxially birefringent material, so that the complex refractive indices of the three linearly independent principal axes therein are different from one another. Preferably, these three principal and different principal axes x, y, and z are located in a Cartesian coordinate system. Therefore, when the angle between the electric field of linearly polarized light or the semimajor axis of elliptically polarized light and the direction of incidence (both projected onto the surface of the filter 5a) is less than 20°, linearly polarized light or elliptically polarized light (especially strongly elliptically polarized light) incident on the optical filter 5a according to the second embodiment at an angle of at least 35° from the third preferred direction is absorbed by at least 85%.

[0074] 4, the wavelength delay of light of wavelength λ satisfies λ=|(n1-n2)|*d, for example, λ=550 nm or 580 nm, or may be any wavelength in the visible wavelength range.

[0075] For example, FIG. 5 shows an exemplary two-dimensional angle-related diagram of the transmittance of the optical filter 5a in the second embodiment, which is a result that can be achieved in the second embodiment, when the wavelength delay of light with wavelength λ satisfies the first condition λ / 2=|(n1-n2)|*d.

[0076] In the first modification of the second embodiment, three different principal axes x, y, and z of the third optical element are arranged in a complex refractive index n x =n2-i×k2, ny=-i×k2, n z = -i × k1, the conditions |n1-n2| × d>λ / 4, k1 / k2>10 are satisfied. In contrast, for the results shown in Figure 5, the delay is set to, for example, 5 / 3*λ. The layer thickness of the absorption transition dipole moment is denoted as d in Figure 5.

[0077] The coordinate direction of the refractive index depends only on the arrangement direction of the principal axes, and is tilted and / or rotated as necessary with respect to the coordinate system of the screen having the optical filter 5a according to the second embodiment.

[0078] In the second modification of the second embodiment, three different principal axes x, y, and z of the third optical element are arranged in a complex refractive index n x =n2-i*k2, n y =-i*k2,n z =n3-i*k1, the conditions k1 / k2>10, |n2-n3|<|n1-n2| / 2 are satisfied. Fig. 6 is a schematic diagram of a two-dimensional angle correlation diagram of transmittance under a second condition of the optical filter in the second embodiment when the wavelength delay of light with wavelength λ satisfies the condition λ / 4=|n1-n2|*d, in which case the delay is set to 5 / 6λ.

[0079] In its second embodiment, the optical filter 5a may further include a device for selectively generating at least a first electric field (EF1) or a second electric field (EF2); a liquid crystal layer 3 arranged in front of or behind the third optical element, on which the first electric field EF1 or the second electric field EF2 acts and which affects the polarization state of the transmitted light depending on the difference in the electric field; thereby the optical filter 5 has different transmission characteristics between a first operating mode B1 in which the first electric field EF1 is applied and a second operating mode B2 in which the second electric field EF2 is applied.

[0080] The beneficial effect of the solution of the present invention is shown in Figures 7 and 8. Figure 7 shows an exemplary angle-related principle diagram of horizontal transmittance (normalized with a maximum of 10°=1 as a reference) of different optical filters when the vertical angle is 0°, and Figure 8 shows the transmittance when the vertical angle is 45°.

[0081] 7 and 8 satisfy the following description. JPEG2025540686000002.jpg63170

[0082] As shown in Figure 7, when the vertical angle is 0°, the influence of the present invention on the transmittance is negligible, and the same is true for the entire horizontal angle range. Since it is generally suitable for practical applications that all transmittances are less than 10, the difference between different filters when the absolute value of the angle is greater than about 60° is negligible.

[0083] In contrast, when the vertical angle is 45°, the difference in transmittance is very significant across the entire range of horizontal angles, as shown in Figure 8. All of the exemplary optical filters described herein clearly reduce transmittance more strongly than the prior art optical filters, particularly in the critical (horizontal) angle ranges of -50° to -25° and 25° to 50°.

[0084] It is particularly significant to apply the present invention to a screen lighting device or a screen. Fig. 9 shows a schematic configuration diagram of a screen lighting device using the optical filter 5 according to the first embodiment or the optical filter 5a according to the second embodiment.

[0085] The illumination device for the screen can operate in at least two operating modes (free-viewing mode B1 and limited-viewing mode B2), and in limited-viewing mode B2, light is emitted within a limited angular range in contrast to the free-viewing mode. a flat extended backlight 8 for emitting light, including the optical filter 5 according to the first embodiment or the optical filter 5a according to the second embodiment; a light guide plate 9 arranged in front of the backlight 8 along the viewing direction and having at least one large surface and / or coupling elements within its volume; a light source 10 arranged laterally on at least one narrow face of said light guide plate 9; a linear polarizing filter P that is arranged in front of the backlight 8 or the light guide plate 9 along the observation direction of the viewer, and that restricts the direction of travel of light that is emitted from the backlight 8 and transmitted through the optical filter 5 or 5a and the linear polarizing filter P; Here, in the limited vision mode B2, the backlight 8 is turned on and the light source 10 is turned off, and in the free vision mode B1, at least the light source 10 is turned on.

[0086] When the filter 5 or 5a of the above-described lighting device includes a liquid crystal layer 3, the operation modes B1 and B2 relate to the states of the liquid crystal layer 3 resulting from the first electric field EF1 and the second electric field EF2, respectively. In this case, when the light source 10 and the backlight 8 are turned on simultaneously, the light transmitted through the backlight 8 not only passes through the filter 5 or 5a but also exits from the side of the light guide plate 9, improving the light extraction efficiency in the free-viewing mode B1. However, even if the filter 5 or 5a does not include the liquid crystal layer 3, the lighting device can still switch between the above-described operation modes because the switching at this time is only between the backlight 8 and the light source 10.

[0087] The present invention further includes a screen that can operate in at least two operating modes (free-viewing mode B1 and limited-viewing mode B2), and in contrast to the free-viewing mode B1, in the limited-viewing mode B2, light is irradiated within a limited angular range relative to the observer. a flat extended backlight 8 for emitting light (optionally arranged to emit light directly (e.g., a so-called matrix backlight)), including the optical filter 5 according to the first embodiment or the optical filter 5a according to the second embodiment (here, both include the liquid crystal layer 3 described above); a linear polarizing filter P, which is placed in front of the backlight 8 along the viewing direction of the screen observer, and which restricts the light emitted from the backlight 8 and transmitted through the filter 5 or 5a and the linear polarizing filter P in its propagation direction; a transmissive display device 11 (preferably an LCD panel) located in front of a backlight 8 and / or a polarising filter P along a viewing direction; Here, in the limited vision mode B2, the second electric field (EF2) is applied, and in the free vision mode B1, the first electric field (EF1) is applied.

[0088] The linear polarizing filter P is preferably provided inside or on top of the transmissive display device 11, or as a part thereof.

[0089] The present invention also includes another screen having a second structure, which can operate in at least two operating modes (free-viewing mode B1 and limited-viewing mode B2), and in contrast to the free-viewing mode B1, in the limited-viewing mode B2, light is irradiated within a limited angular range relative to the observer. Figure 11 shows a schematic diagram of such a screen, which includes: a display device 12, for example an OLED panel, a micro LED panel, an LCD panel or any other type of screen; and an optical filter 5 or 5a according to the first or second embodiment of the present invention (each including the liquid crystal layer described above) disposed in front of the display device 12 along the viewing direction of the viewer; Here, in the limited vision mode B2, the second electric field (EF2) is applied, and in the free vision mode B1, the first electric field (EF1) is applied.

[0090] Optionally, a polarizing filter P and / or a retardation layer (not shown), preferably a λ / 4 type retardation layer (which converts circularly polarized light into nearly linear or strongly elliptically polarized light), is provided between the display device 12 and the optical filter 5 or 5a of the present invention.

[0091] Finally, FIG. 12 shows a schematic diagram of a third configuration of a screen that can operate in at least two operating modes (free-viewing mode B1 and limited-viewing mode B2) using the optical filter 5 according to the first embodiment or the optical filter 5a according to the second embodiment. For a screen having the above-described transmissive display device 11 (particularly an LCD panel), a backlight 8a is further provided. Therefore, a third configuration embodiment can be adopted in which the backlight 8a is designed to have a horizontally asymmetric luminance distribution that is substantially not symmetrical about the vertical centerline of the viewer's viewing angle. This can be achieved by using a turning film, an asymmetric diffuser, and / or an asymmetric louver film. That is, the backlight 8a has an asymmetric luminance distribution, and preferably, the asymmetry exists in the horizontal direction of the viewer.

[0092] This type of screen with the third structure is particularly suitable for vehicle applications because the backlight 8a design significantly reduces the light emitted toward the passenger window at a horizontal angle of 25° or more (relative to the vertical centerline), for example, to less than 10% (preferably less than 2.5%) of peak brightness, while maintaining high brightness for the light toward the driver. This also reduces ambient reflections from the passenger window and passenger side mirror. Nevertheless, since a filter 5 or 5a is provided in front (or behind) of the image display device 11, the screen can be selectively operated so that only the passenger in the passenger seat can view the image content (restricted viewing mode B2, e.g., for playing video), or so that both the driver and passenger can view the image content (free viewing mode B1, e.g., for displaying a navigation map).

[0093] The present invention solves the above-mentioned problem by providing an optical filter having an optical element that transmits, partially absorbs, or completely absorbs light incident on the optical element depending on the incident direction and polarization characteristics. By using an optical filter including this optical element, the light transmittance can be adjusted according to the angle (selectively perpendicular to a seated or standing observer) and at least two operating states can be selectively switched. At the same time, the transmittance is reduced when the vertical viewing angle is greater than 5° (i.e., improving anti-peeping), while maintaining the transmittance when the vertical viewing angle is less than 5°.

[0094] The present invention can be used in combination with a display device and is applicable to situations where private data needs to be displayed and / or entered, such as entering a PIN code or display data at an ATM or payment terminal, entering a password, or viewing email on a mobile device. Thus, the present invention can also be applied to passenger vehicles, where image content can be selectively prevented from interfering with the driver or passenger in the front seat. [Explanation of symbols]

[0095] 1: First optical element 2: Second optical element 3: LCD 4: Incident light direction 4a: Projection of incident direction 4 5: Optical filter according to the first embodiment 5a: Optical filter according to the second embodiment 6: Optical filter according to the second embodiment 6a: Projection of semimajor axis 6 7: Retardation layer 8: Backlight 8a: Backlight with asymmetric light density distribution 9: Light guide plate 10: Light source 11: Transparent display device 12: Display device P: Polarizing filter (linear)

Claims

1. An optical filter (5), A first optical element (1), a second optical element (2), and a retardation layer (7), each of the first optical element (1) and the second optical element (2) comprises a plurality of optical absorption transition dipole moments, and the first optical element (1) and the second optical element (2) are stacked along a direction of incidence of light (4), wherein a majority of the transition dipole moments of the plurality of transition dipole moments are arranged to be parallel to or vary around a first preferred direction selectable for the first optical element (1) and a second preferred direction selectable for the second optical element (2) with a tolerance of at most 20°, at least in a first state, 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 (4) and its polarization state relative to the corresponding optical element (1, 2); the retardation layer (7) is in the form of a C-plate or an A-plate and is arranged between the first optical element (1) and the second optical element (2), and for a given wavelength λ, a retardation of greater than λ / 4 is generated by the retardation layer (7), so that at least 85% of linearly polarized or elliptically polarized light incident on the filter (5) at an angle of at least 35° to the first preferred direction or the second preferred direction is absorbed, wherein the angle between the electric field of the linearly polarized light or the major semi-axis (6) of the elliptical polarization when projected onto the surface of the filter (5) and the direction of incidence (4) is less than 20°.

2. a device for selectively generating the first electric field (EF1) or the second electric field (EF2); and 2. The optical filter (5) of claim 1, characterized in that it comprises a liquid crystal layer (3) arranged above or below the first optical element (1) and / or the second optical element (2), wherein the first electric field (EF1) or the second electric field (EF2) acts on the liquid crystal layer, the liquid crystal layer influencing the polarization state of light passing through the liquid crystal layer by the first electric field (EF1) or the second electric field (EF2), such that the filter (5) has different transmission characteristics in a first operating mode B1 in which the first electric field (EF1) is applied and in a second operating mode B2 in which the second electric field (EF2) is applied.

3. An optical filter (5a), a third optical element; the third optical element includes a plurality of absorbing transition dipole moments, wherein a majority of the transition dipole moments of the plurality of transition dipole moments are arranged to be parallel to or vary about a selectable third preferred direction for the third optical element with a tolerance of up to 20° at least in a first state, such that light incident on the third optical element is transmitted or at least partially absorbed depending on the direction of incidence and its polarization state relative to the corresponding third optical element; the third optical element is made of a biaxially birefringent material, and the three complex refractive indices of the three major axes (x, y, z) in the third optical element are different from one another, such that linearly polarized or elliptically polarized light incident on the filter (5a) at an angle of at least 35° to the third preferred direction is absorbed by at least 85%, wherein the angle between the electric field of the linearly polarized light or the semimajor axis (6) of the elliptical polarized light and the direction of incidence (4) projected onto the surface of the filter (5a) is less than 20°.

4. The optical filter (5a) according to claim 3, characterized in that the three principal axes (x, y, z) of the third optical element have complex refractive indices nx = n2 - i × k2, ny = n1 - i × k2, and nz = n1 - i × k1, respectively, and satisfy |n1 - n2 | d ≧ λ / 4 (k1 / k2 > 10).

5. The three principal axes (x, y, z) of the third optical element each have a complex refractive index n ｘ = n ２ -i × k ２ , n ｙ = n １ -i × k ２ and n ｚ = n ３ -i × k １ and |n １ -n ２ |d≧λ / 4(k １ / k ２ >10 and |n ２ -n ３ |≦|n １ -n ２ 4. The optical filter (5a) according to claim 3, characterized in that it satisfies | / 2).

6. a device for selectively generating the first electric field (EF1) or the second electric field (EF2); and The optical filter (5a) according to any one of claims 3 to 5, characterized in that it comprises a liquid crystal layer (3) arranged above or below the third optical element, wherein the first electric field (EF1) or the second electric field (EF2) acts on the liquid crystal layer, the liquid crystal layer affects the polarization state of light passing through the liquid crystal layer by the first electric field (EF1) or the second electric field (EF2), and the optical filter (5a) has different transmission characteristics in a first operating mode B1 in which the first electric field (EF1) is applied and in a second operating mode B2 in which the second electric field (EF2) is applied.

7. 1. An illumination device for a screen, comprising: The illumination device is operable in at least one of an operation mode B1 corresponding to a free-vision mode and an operation mode B2 corresponding to a limited-vision mode, wherein a viewing angle range in which light is emitted in the limited-vision mode is limited compared to the free-vision mode, and A flat extended backlight (8) for emitting light, comprising an optical filter (5, 5a) according to any one of claims 1 to 6; a light guide plate (9) located in front of the backlight (8) along the viewing direction of the viewer and having at least one large surface and / or coupling elements within its volume; a light source (10) disposed laterally on at least one narrow surface of the light guide plate (9); and a linear polarizing filter (P) that is arranged in front of the backlight (8) or the light guide plate (9) along the observation direction, and that limits the direction of travel of light that is emitted from the backlight (8) and transmitted through the optical filter (5, 5a) and the linear polarizing filter (P); Here, in the operation mode B2, the backlight (8) is turned on and the light source (10) is turned off, and in the operation mode B1, at least the light source (10) is turned on.

8. A screen, The screen is operable in at least one of an operation mode B1 corresponding to a free-viewing mode and an operation mode B2 corresponding to a limited-viewing mode, wherein the viewing angle range in the limited-viewing mode from which light is emitted is limited relative to the free-viewing mode, and the screen is a flat extended backlight (8) for emitting light, comprising the optical filter (5) according to claim 2 or the optical filter (5a) according to claim 6; a linear polarizing filter (P) that is arranged in front of the backlight (8) or the light guide plate (9) along the observation direction of the observer, and that restricts the light that is emitted from the backlight and transmitted through the optical filter (5, 5a) and the linear polarizing filter (P) to its traveling direction; and a transmission type display device (11) arranged in front of the optical filter (5, 5a) along the observation direction; Here, in the operation mode B2, the second electric field (EF2) is applied, and in the operation mode B1, the first electric field (EF1) is applied.

9. 9. A screen according to claim 8, characterized in that the linear polarizing filter (P) is provided in or is part of the transmissive display device (11).

10. A screen, The screen is operable in at least one of an operation mode B1 corresponding to a free-viewing mode and an operation mode B2 corresponding to a limited-viewing mode, wherein the viewing angle range in the limited-viewing mode from which light is emitted is limited relative to the free-viewing mode, and the screen is a display device (12); and The optical filter (5) according to claim 2 or the optical filter (5a) according to claim 6, which is arranged in front of the display device (12) along the viewing direction of a viewer; Here, in the operation mode B2, the second electric field (EF2) is applied, and in the operation mode B1, the first electric field (EF1) is applied.

11. A screen, The screen is operable in at least one of an operation mode B1 corresponding to a free-viewing mode and an operation mode B2 corresponding to a limited-viewing mode, wherein a viewing angle range in which light is emitted in the limited-viewing mode is limited relative to the free-viewing mode, and the screen is Transmissive display device (11); A backlight (8a) having an asymmetric light density distribution, which is installed behind the transmission type display device (11) along the viewing direction of the viewer; and The optical filter (5) according to claim 2 or the optical filter (5a) according to claim 6, Here, in the operation mode B2, the second electric field (EF2) is applied, and in the operation mode B1, the first electric field (EF1) is applied.

12. 12. The screen according to claim 11, wherein the asymmetric light density distribution exists in the horizontal direction of the viewing angle from the observer.

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