Backlights and illumination devices with optical films, screens and optical films

Abstract

This invention relates to a backlight (13) that extends planarly, emits light, and has an optical film for controlling and limiting the viewing angle range of a viewer. The optical film, viewed from the viewer's direction, comprises: a first polarizing layer (1) having a first absorption axis at an angle of 0° to 30° to the surface normal of the optical film; at least one phase-shift compensation layer for improving the limitation of the viewing angle range; and a second polarizing layer (2) having a second absorption axis parallel to the surface of the optical film. According to the invention, various technical solutions and combinations thereof are provided with a spatially uniform compensation layer composed of a uniaxial or biaxial birefringent material, wherein the material and thickness of the compensation layer are specified such that the luminous density is minimized within a specified solid angle range, which excludes the entire half-space except for a cone recessed along the viewing direction.

Description

Technical Field

[0001] This invention relates to a backlight that is planar, extends, emits light, and has an optical film for controlling and limiting the viewing angle range of a viewer. The invention also relates to the optical film. This film includes a first polarizing layer with a first absorption axis and a second polarizing layer with a second absorption axis. The first absorption axis forms an angle of 0° to 30° with the surface normal of the optical film, and the second absorption axis is parallel to the surface of the optical film. At least one phase-shift compensation layer is disposed therebetween to improve the limitation of the viewing angle range. Viewed from the viewer's direction, the first polarizing layer or the second polarizing layer can form the layer closest to the viewer.

[0002] Significant progress has been made in recent years in expanding the viewing angle of LCDs. However, the extreme viewing area of ​​a screen often becomes a disadvantage. Increasingly, information, such as banking data or other personal information, as well as sensitive data, can be provided on portable devices like laptops and tablets. Accordingly, people need to control who is allowed to see this sensitive data; they need the ability to choose a wide viewing angle, or a public viewing mode, to share information on the display with others, such as when viewing holiday photos or for advertising purposes. On the other hand, a smaller viewing angle, or a private viewing mode, is needed to maintain the confidentiality of the image information.

[0003] A similar problem exists in the automotive manufacturing industry: once the engine is started, drivers cannot afford to be distracted by visual content such as digital entertainment programs, while passengers expect to be able to watch content while driving. Therefore, a screen that can switch between corresponding presentation modes is needed.

[0004] Microsheet-based supplementary films have been used in portable displays to provide visual data protection. However, these films are not switchable or convertible; they must always be applied by hand and then removed. They also must be shipped separately from the display when not in use. Another major drawback of using such sheet films is light loss. Background Technology

[0005] US 6,765,550 B2 describes this type of privacy protection achieved through microlayers. The biggest drawback of this approach is the mechanical removal and attachment of the filter, as well as the light loss in the protection mode.

[0006] US 5,993,940 A describes the use of a thin film with small strip-shaped prisms uniformly distributed on its surface to achieve a privacy mode, i.e., a restricted viewing mode with a small field of view. The research and manufacturing of this technology presents considerable technical challenges.

[0007] In WO 2012 / 033583 A1, switching between free and restricted viewing horizons is achieved by controlling the liquid crystals between the so-called "color-emitting" layers. This process results in light loss and is technically quite challenging.

[0008] US2012 / 0235891 A1 describes an extremely complex screen backlight. According to Figures 1 and 15 of that case, it not only uses several light guides but also other complex optical elements, such as a microlens assembly 40 and a prism structure 50, which shape the light originating from the rear illumination along the path to front illumination. This is costly, technically challenging, and also results in light loss. According to the variant shown in Figure 17 of US2012 / 0235891A1, both light sources 4R and 18 produce light with narrow illumination angles, where the light from the rear light source 18 undergoes a complex process before being transformed into light with a wide illumination angle. As mentioned earlier, such a complex transformation significantly reduces brightness.

[0009] According to JP 2007-155783 A, a special optical surface 19, which is complex to calculate and manufacture, is used to deflect light to different narrow or wide regions depending on the angle of incidence. This structure is similar to a Fresnel lens. However, there are interfering sides that deflect light in unwanted directions. Therefore, it is uncertain whether a truly reasonable light distribution can be achieved.

[0010] US2013 / 0308185 A1 describes a special light guide with stepped sections that emits light in different directions on a large surface, depending on which direction the light guide is illuminated from the narrow side. When used in conjunction with a transmissive image reproduction device such as an LC display, a screen that can switch between free-viewing and restricted-viewing modes can be created. Its main drawback is that the restricted-viewing effect can only be produced on the left / right or up / down, but not simultaneously on both sides, which is necessary for certain payment processes, for example. Furthermore, even in restricted-viewing mode, residual light can still be seen from the obstructed viewing angle.

[0011] The applicant's WO 2015 / 121398 A1 describes a screen with two operating modes, wherein scattering particles are present in the volume of the corresponding light guide to achieve the switching of operating modes. However, the polymer scattering particles selected in this application generally have the following drawbacks: light is coupled outward from two large surfaces, so approximately half of the useful light is emitted in the wrong direction, i.e., towards the backlight direction, and due to structural reasons, it cannot be sufficiently recovered at that location. Furthermore, depending on the situation, especially at higher concentrations, the polymer-based scattering particles distributed in the volume of the light guide may cause scattering effects, which will weaken the privacy protection effect in the protected operating mode.

[0012] The basic idea behind "electro-induced birefringence (EDB)" technology is to use switchable liquid crystals in an additional coated LC panel to "filter" all light beams that do not exit from the imaging layer at a specific beam angle. The disadvantages of this technology include higher energy consumption and cost, and difficulty in changing the optimal point of + / -40°, i.e., the best viewing position. The absorption of the LC structure is also insufficient because once the viewing angle exceeds the sweet spot, the light intensity attenuation will increase again; therefore, for viewing angles greater than + / -40°, the light intensity is at most 3% of the maximum light intensity.

[0013] US2019 / 0094626 A1 describes an optical layer structure for controlling or limiting viewing angles, in which two phase plates are arranged on a linear polarizer as compensation layers. These two phase plates are λ / 4 plates, which have several structured, optically anisotropic, fin-like or strip-like layers, each with a carrier material arranged between it. They can have the same structure but differ in orientation after arrangement. The uppermost layer forms a polarization layer, in which the absorption axis of the transition dipole moment used to achieve polarization is oriented in a direction perpendicular to the layer surface, i.e., a so-called "Z-polarizer". In this type of layer with finned structure, visual artifacts such as moiré fringes may still occur. Therefore, this type of layer can only be applied to screens whose resolution, size, aperture, scattering characteristics, and distance from the screen surface are known, and cannot be used universally or independently of screen size.

[0014] The methods and configurations described above generally have the following drawbacks: they significantly reduce the basic screen brightness and / or require complex and expensive optical components for mode switching and / or reduce the resolution in public viewing modes and / or cause visual artifacts when using displays with extremely high resolution. Another drawback is that the limitation of the viewing angle is not thorough; although the viewing angle should be limited, it is still possible to identify image content with significantly reduced brightness, which can interfere with nighttime driving, for example. Summary of the Invention

[0015] The purpose of this invention is to develop a backlight having an optical film for controlling and limiting the viewing angle of a viewer looking at the film—which is typically combined with a screen—thereby improving the limitation of the viewing angle and making it more difficult for unauthorized users to peek at protected image content, i.e., further improving the so-called privacy effect.

[0016] Regarding optical thin films having the aforementioned layer structure and backlights having such optical thin films, the solution of the present invention for achieving the above-mentioned objectives is a specific technical solution for the at least one compensation layer, wherein the first polarizing layer and the second polarizing layer are first described in detail. The first polarizing layer has a first absorption axis that forms an angle of 0° to 30° with the surface normal of the optical thin film. When the angle is 0°, that is, when the absorption axis is parallel to the surface normal or perpendicular to the surface of the thin film, it is referred to as a so-called "Z polarizer". When the angle is different and within the aforementioned range of a maximum of 30°, it is also referred to hereinafter as a "Z* polarizer". The absorption of the first polarizing layer is usually static, but a switchable scheme can also be adopted, so that the angle-related absorption can be turned on and off. The second polarizing layer has a second absorption axis, wherein the second absorption axis is parallel to the surface of the optical thin film. Therefore, the second polarizing layer is a conventional linear polarizer. At least one phase shift compensation layer for improving the limitation of the viewing angle range is arranged between the first polarizing layer and the second polarizing layer. Both the first polarizing layer and the second polarizing layer can be closest to the viewer. Preferably, all layers are fixedly connected, for example, by material bonding, by welding or by optical adhesion.

[0017] For ease of understanding, it is generally assumed in the following text that the thin film surface lies in a plane in the rectangular coordinate system formed by the x, y, and z directions, and this plane is parallel to the xy plane formed by the x and y directions. Therefore, the surface normal is parallel to the z direction.

[0018] To improve privacy, i.e., to reduce the limitation on the viewing angle range, the at least one phase shift compensation layer can be constructed in principle in two ways. In the first alternative—hereinafter also referred to as alternative i—a first B* compensation layer is arranged between the first polarization layer and the second polarization layer, which is composed of a first biaxial birefringent material. The biaxial birefringent material has two optical axes and three principal refractive axes, each principal refractive axis corresponding (birefringently) to a refractive index n. x n y n z Depending on the technical solution of the first B* compensation layer and the orientation of its optical axis, the principal refractive axis corresponding to either the minimum refractive index or the maximum refractive index is parallel to the first absorption axis. The first B* compensation layer satisfies the following condition:

[0019]

[0020] Where d represents the thickness of the first compensation layer, Δph represents the phase shift caused by the first B* compensation layer, and λ represents the wavelength that is arbitrarily defined in principle to satisfy this condition. This defines the upper limit of the phase delay of the B* compensation layer, which also indirectly defines the maximum thickness.

[0021] In the second alternative—hereinafter also referred to as Alternative ii—at least two compensation layers made of uniaxial birefringent materials are arranged between the first polarization layer and the second polarization layer. The spatially uniform first A* compensation layer is composed of a first uniaxial birefringent material having a first optical axis and two distinct first principal refractive axes. The first optical axis coinciding with one of the first principal refractive axes is perpendicular to or parallel to the first absorption axis of the first polarization layer. Viewed from the observer's direction, a spatially uniform second A* compensation layer is arranged behind it, composed of a second uniaxial birefringent material having a second optical axis and two second principal refractive axes. The second optical axis of the second material coinciding with one of the second principal refractive axes is perpendicular to the first optical axis of the first material. The optical axes of these uniaxial materials are also called special axes.

[0022] "Spatial uniformity" here refers to the fact that the corresponding compensation layer is not structured within its interior or along the area parallel to the surface of the optical film, thus possessing the same characteristics over the entire area, which differs from, for example, from US2019 / 0094626 A1. To prevent visual artifacts on such layered structures, according to a technical solution in US2019 / 0094626 A1, the layer structure must be specifically adjusted for each configuration in terms of resolution, distance, aperture, surface area, and scattering characteristics, which increases manufacturing costs. In contrast, the optical film of this invention, with its spatially uniform compensation layer, can be universally applied to various screen sizes and resolutions without requiring specialized adjustments.

[0023] Each of the two A* compensation layers satisfies the condition.

[0024]

[0025] Where d represents the thickness of the corresponding A* compensation layer, n e To represent a special refractive index, n o This represents the normal refractive index. Δph represents the phase shift caused by the first A* compensation layer or the second A* compensation layer, respectively, and λ represents the wavelength that is arbitrarily specified in principle to satisfy this condition.

[0026] In both alternatives, the material and thickness d of the compensation layer are specified such that, in a spherical coordinate system with the origin located on the film surface and in the film plane, the luminescence density is minimized only within a specified solid angle range R. The solid angle range R only includes a portion of the possible perceptible half-space, i.e., it includes the azimuth angle. The preferred orientation for measurement is in the plane relative to the film surface. or Less than the specified limit azimuth angle φ limThe absolute value. In principle, the preferred direction can be chosen arbitrarily, but it should be based on the application of the optical film. When such an optical film is applied, for example, to a screen with a fixed orientation (such as in a vehicle), the preferred direction is chosen to be parallel to the imaginary line between the eyes of an upright driver, that is, usually extending horizontally.

[0027] On the other hand, the solid angle range for minimum luminous density also includes the polar angle θ, which, when measured relative to the first absorption axis and in the plane formed by the surface normal and the first absorption axis (whose vectors share a common origin), has an absolute value greater than the specified limiting polar angle θ. lim That is, there is a limiting polar angle θ around the first absorption axis (which is referred to here as the "zero axis"). lim All solid angles outside the cone. When the surface normal is parallel to the first absorption axis, the polar angle is measured only relative to the surface normal. When this optical film is applied to the screen exemplarily described above, it effectively limits the line of sight because the luminous density is minimal within the aforementioned solid angle range. Therefore, ideally, a viewer positioned within the aforementioned solid angle range relative to the spherical coordinate system of the optical film will not perceive any content on the screen due to the minimum luminous density within this range. The term "minimum luminous density" refers to a luminous density approximately zero, where the luminous density drops significantly compared to the luminous density outside the aforementioned solid angle range, making it ideally impossible for a viewer to see any image content.

[0028] To more clearly define the solid angle range, i.e. to achieve a greater decrease in luminous density inside compared to the luminous density outside the solid angle range, in the second alternative ii, a spatially uniform third C* compensation layer is advantageously arranged between the first A* compensation layer and the second A* compensation layer. This third C* compensation layer is composed of a third uniaxial birefringent material having a third optical axis and two third principal refractive axes, wherein the third optical axis is parallel to the first absorption axis of the first polarization layer.

[0029] To achieve a symmetrical decrease in luminous density relative to the film surface, the first absorption axis is perpendicular to the film surface. When using this optical film in the aforementioned screen, a viewer looking at the screen along the surface normal perceives a symmetrical decrease in luminous density depending on whether the viewing angle is to the right, left, or along a preferred direction; that is, it is only related to the absolute value of the polar angle. In this case, the limiting polar angle θ... lim It is measured relative to the surface normal, and therefore is the same for all azimuth angles, unlike measurements relative to the first absorption axis.

[0030] When the first absorption axis is oriented in this way, the first polarization layer is also called the Z-polarization layer. When the first absorption axis is oriented differently within the aforementioned range, the first polarization layer is called the Z* polarization layer. In other words, the use of the symbol "*" here indicates the generalization of the Z-polarization layer.

[0031] Similarly, the name A* compensation layer represents the generalization of the term A compensation layer, and the name B* compensation layer represents the generalization of the term B compensation layer. For the definitions of the previously known names “Z polarization layer,” “A compensation layer,” and “B compensation layer,” see “Optical anisotropy conversion of retarder film made of rodlike and crosslike reactive molecules, and its dependence on the relative ratio and the orientation of the constituent molecules,” by Ho-Jin Choi et al., published online in *Optical Materials* 99 (2020), document number 109531.

[0032] When the first absorption axis is perpendicular to the thin film surface, i.e., the first polarization layer is constructed as a Z-polarization layer, several advantageous technical solutions arise. Two of these solutions address the first alternative, and a third addresses the second alternative. The orientation of the optical axis of this compensation layer must, in principle, correspond to the orientation of the first absorption axis of the first polarization layer to achieve the desired limitation of the visible area. For example, if the viewer, such as a vehicle driver, is not looking at the screen along the surface normal but from an oblique angle, the first absorption axis can preferably be positioned differently.

[0033] In the first technical solution based on the first alternative, the first absorption axis of the first polarizing layer is perpendicular to the surface of the optical thin film, and the principal refractive axis corresponding to the minimum refractive index is parallel to the first absorption axis. In this technical solution, the first B* compensation layer is constructed as a -B compensation layer. This optical axis lies in the plane formed by the x and z directions, and the three principal refractive axes correspond to the directions of this rectangular coordinate system, where n... x >n y >n z And n x The second absorption axis is parallel to the second polarization layer. This latter condition also applies to a small tilt angle of approximately 10° relative to the surface normal of the first absorption axis; otherwise, the principal refraction axis will also be tilted. Furthermore, the orientation of the coordinate system in the x, y, and z directions is based on the orientation of the first absorption axis, corresponding to the z-direction of the coordinate system. The essential point here is that n... x Perpendicular to the first absorption axis.

[0034] In the second technical solution based on the first alternative, the first absorption axis of the first polarizing layer is perpendicular to the optical thin film surface, and the principal refractive axis corresponding to the maximum refractive index is parallel to the first absorption axis. In this technical solution, the first B* compensation layer is constructed as a +B compensation layer. This optical axis lies in the plane formed by the y and z directions, and the three principal refractive axes correspond to the directions of this rectangular coordinate system, where n... z >n x >n y And n y The second absorption axis is parallel to the second polarization layer. This latter condition also applies to a small tilt angle of approximately 10° relative to the surface normal of the first absorption axis; otherwise, the principal refraction axis will also be tilted. Furthermore, the orientation of the coordinate system in the x, y, and z directions is based on the orientation of the first absorption axis, corresponding to the z-direction of the coordinate system. The essential point here is that n... y Perpendicular to the first absorption axis.

[0035] In the third technical solution based on the second alternative, the first absorption axis of the first polarizing layer (1) is also perpendicular to the surface of the optical thin film. In this technical solution, the first A* compensation layer is constructed as a +A compensation layer, the second A* compensation layer is constructed as a -A compensation layer, or vice versa. When a third C* compensation layer is provided, it is constructed as a -C or +C compensation layer.

[0036] In order to keep manufacturing costs low, the first A* compensation layer and the second A* compensation layer preferably have the same structure, that is, the two compensation layers are either both constructed as +A compensation layers or both constructed as -A compensation layers and have the same thickness.

[0037] In all the foregoing technical solutions, according to a particularly preferred embodiment, a liquid crystal layer switchable between at least two states is arranged between the second polarization layer and the compensation layer closest to the second polarization layer. This liquid crystal layer is configured to transmit light transmitted by the second polarization layer with linear polarization in a first switching state (either unchanged or rotated by 90°), and to transmit the light in a circular, elliptical, or linearly polarized manner in a second switching state. In the first switching state, a 90° rotation means that the linearly polarized light becomes linearly or elliptically polarized light after passing through the switchable liquid crystal layer, where most of the electric field vector rotates by 90°. That is, the polarization is not exactly rotated by 90°. The addition of the switchable liquid crystal layer allows switching between a privacy mode and a public mode, which is particularly noticeable when the optical thin film is integrated into the screen. The previously described decrease in luminous density within a specified solid angle range is persistent for optical thin films but can be eliminated by using a switchable liquid crystal layer. The first switching state corresponds to the privacy mode, where the light remains linearly polarized. The second switching state corresponds to the public mode, where the light is typically elliptically polarized, but other polarization methods may be used depending on the selected liquid crystal layer. In public mode, the luminous density does not decrease or only decreases slightly within the specified solid angle range. Therefore, if this arrangement is used in a screen, the image content can be perceived (i.e., without restriction) within the technically feasible range, regardless of the viewer's position. In privacy mode, the image content cannot be perceived by a person standing sideways (relative to the direction of the first absorption axis). Alternatively, the liquid crystal layer can also be arranged between the first polarizing layer and the compensation layer closest to it.

[0038] This switchable liquid crystal layer is typically used in conjunction with a static first polarizing layer to fabricate a switchable optical thin film. If the function of the switchable liquid crystal layer can be achieved by the switchable first polarizing layer, then the switchable liquid crystal layer may not be necessary. In this case, the first polarizing layer can be constructed, for example, as a liquid crystal layer embedded with a dye, known as a "Dye-LC-Zellen" (dye LC cell). This type of liquid crystal layer is particularly suitable when the first absorption axis, i.e., the absorption axis of the first polarizing layer, is parallel to the surface normal of the optical thin film.

[0039] Ideally, the line-of-sight limitation effect within a specified solid angle range, i.e., the luminous density decreases to a minimum within this solid angle range, is achieved by coordinating the components of the optical thin film to ensure that the loss function is minimized within the specified solid angle range R.

[0040] C2=∫ R lnT(φ,θ)dΩ

[0041] Minimum, of which Let Ω be the angle-dependent transmittance, and Ω be the solid angle. That is, the natural logarithm of the angle-resolved transmittance is calculated and integrated over the solid angle range where privacy protection needs to be optimized. This logarithm is weighted to account for different orders of magnitude of transmittance during optimization. Other weighting methods, such as linear weighting, can also be used. In this case, the logarithm does not need to be applied to the transmittance. Commercially available optical design programs can be used to coordinate the components and implement the optical design of this invention, such as Uniglobe Kisco's LCD. Or INCROPS' TecwizLCD

[0042] In common applications, the limiting azimuth angle φ is preferred. lim The preferred direction is 30° to 40° to the left and right, and / or the extreme polar angle θ. lim The angle is 40° to 50° to the left or right of the surface normal or the direction of the first absorption axis (if it is inclined relative to the surface normal).

[0043] When the thin film is not equipped with the aforementioned switchable liquid crystal layer, the backlight with the aforementioned optical thin film can be integrated into the screen's lighting device; when the thin film is equipped with the switchable liquid crystal layer, the backlight can be integrated into the screen.

[0044] Specifically, a backlight having a non-switchable optical film (i.e., without a switchable liquid crystal layer) can be inserted into and applied to an illumination device for a transmissive screen (especially an LC display). This illumination device is configured to operate in two modes: B1 (for free viewing mode) and B2 (for restricted viewing mode), in which light is emitted over a more limited solid angle range compared to the free viewing mode. The illumination device includes a planar backlight that emits light, having a backlight source and the aforementioned non-switchable optical film. If a second polarizing layer of the optical film is arranged in front of the first polarizing layer along the viewing direction, then for the backlight as a whole (as in other technical solutions described below): the backlight source emits unpolarized light; with the opposite arrangement, the light emitted by the backlight source is (partially) polarized. For a viewer looking at the lighting device, a plate-shaped light guide is arranged in front of the backlight along the viewing direction. This guide has two large surfaces and a narrow side connecting them, and has an output coupling element on at least one of these large surfaces and / or within its volume. A light-emitting element is laterally arranged on at least one narrow side of the light guide. A linear polarizing filter is arranged in front of the backlight or the light guide along the viewing direction. Optionally, this polarizing filter may correspond to a second polarizing layer of an optical film, or a special configuration may be used. This restricts the propagation direction of light originating from the backlight and passing through the linear polarizing filter. In operating mode B2 for the restricted viewing mode, the backlight is on, and the light-emitting element is off. Only the backlight emits light into the restricted viewing angle range. In operating mode B1 for the free or public viewing mode, at least this light-emitting element is on, thereby compensating for or overcompensating for the restricted illumination achieved solely by the backlight. Accordingly, the backlight can be turned on or off in the public viewing mode. In this case, the transmissive screen is arranged in front of the lighting device.

[0045] The invention also includes a screen operable in at least two operating modes, B1 (for free viewing mode) and B2 (for restricted viewing mode), in which light is emitted to a viewing angle or solid angle range that is more limited for the viewer compared to free viewing mode. In a technical solution with a switchable liquid crystal layer that can switch between the two states, such a screen first includes a planar extended backlight emitting light, having the aforementioned optical film. Optionally, the backlight can emit light directly, for example, implemented as a so-called "direct matrix backlight." A linear polarizing filter is arranged in front of the backlight along the viewing direction. Optionally, the polarizing filter may also correspond to a second polarizing layer of the optical film. This restricts the propagation direction of light originating from the backlight and passing through the linear polarizing filter. A transmissive image reproduction device is arranged in front of the backlight along the viewing direction. The linear polarizing filter may be part of the image reproduction device and arranged within it. The polarizing filter can also be used independently, where it is positioned as close as possible to the image reproduction device within the stack of optical elements. A typical image reproduction device has a linear polarizer above and below the LC layer along the viewing direction; the previous description here refers to the linear polarizer located below along the viewing direction. The upper linear polarizer is crucial for privacy protection applications. As previously mentioned, the liquid crystal layer, which can switch between at least two states, is in a first switching state in operating mode B2 and a second switching state in operating mode B2.

[0046] Finally, the invention also includes another screen that can operate in at least two operating modes, B1 (for free viewing mode) and B2 (for restricted viewing mode), in which light is emitted to a viewing angle or solid angle range that is more limited for the viewer compared to the free viewing mode. This screen includes an image reproduction device of, for example, OLED, microLED, or LCD type, and an optical film disposed in front of the image reproduction device along the viewing direction, the optical film having the aforementioned liquid crystal layer that can switch between at least two states. According to the previous definitions of the first and second switching states, the liquid crystal layer is in the first switching state in operating mode B2 and in the second switching state in operating mode B2.

[0047] Of course, within the scope of this invention, the features described above and below can be combined not only in the manner given in this application, but also in other combinations or individually. Attached Figure Description

[0048] The invention will now be described in detail with reference to the accompanying drawings, which reveal the essential features of the invention, and in conjunction with embodiments. These embodiments are for illustrative purposes only and do not constitute limitation. For example, the description of an embodiment comprising multiple elements or components does not imply that all such elements or components are indispensable. Specifically, other embodiments may also include alternative elements and components, reduced elements or components, or additional elements or components. Unless otherwise stated, elements or components of different embodiments may be combined with each other. Variations and variations described in one embodiment may also be applied to other embodiments. To avoid repetition, the same or corresponding elements in different drawings are represented by the same symbols and will not be described again. Wherein:

[0049] Figures 1A to 1C Various layer structures for optical thin films used to control and limit the viewer's field of view.

[0050] Figure 2 To limit the field of view,

[0051] Figure 3 This invention provides an example of how to improve privacy protection.

[0052] Figure 4A and 4B The privacy protection effect of the first technical solution for optical thin films,

[0053] Figure 5A and 5B The privacy protection effect of the second technical solution for optical thin films,

[0054] Figure 6A and 6B The third technical solution for privacy protection of optical thin films.

[0055] Figures 7A to 7G For the polarization ellipse passing through the optical thin film,

[0056] Figure 8 A switchable solution for optical thin films.

[0057] Figure 9A and 9B These represent the two operating states of an illumination device with a non-switchable optical thin film.

[0058] Figure 10 For screens with switchable optical films, and

[0059] Figure 11 For another screen with a switchable optical film. Detailed Implementation

[0060] Figures 1A to 1CThis is a schematic diagram of various layer structures for optical thin films used to control and limit the viewer's field of view. The viewer (not shown) is positioned above the topmost layer, which has a surface with a surface normal that is parallel to the long side of the page in the drawing plane. This topmost layer, viewed from the viewer's direction, is visible in all three viewing angles. Figures 1A to 1C The first polarizing layer 1 is used in both cases. The first polarizing layer 1 has a first absorption axis that forms an angle of 0° to 30° with the surface normal of the optical thin film. When the angle is 0°, the first polarizing layer 1 is a Z-polarizer; when the angle is different, the term "Z* polarizer" is used. A 0° angle is suitable, for example, for a laptop computer where the user is directly in front of the screen. A 30° angle is advantageous, for example, in a motor vehicle where the screen is positioned between the driver's seat and the passenger seat, so that only the driver can see the relevant information.

[0061] Figures 1A to 1C The bottom layer is a second polarization layer 2 with a second absorption axis parallel to the surface of the optical thin film. In other words, the second polarization layer 2 here is a linear polarizer.

[0062] At least one phase-shift compensation layer is disposed between the first polarizing layer 1 and the second polarizing layer 2 to improve the limitation of the viewing angle range. A single compensation layer or multiple compensation layers may be used, depending on the type of compensation layer. Such compensation layers are, for example, uniaxial or biaxial birefringent polymer films. These layers are advantageously fixed together, for example, by optical adhesive or other material bonding. Ultrasonic welding may also be used, for example. When extremely smooth surfaces are placed or pressed together, the connection can also be achieved solely by adhesive, with an anti-reflective layer used as needed. Schemes involving one or more compensation layers can be employed to improve privacy, as will be described below. In an alternative not shown, the second polarizing layer 2 may also be arranged as the uppermost layer along the viewing direction, with the first polarizing layer 1 disposed behind it, wherein the at least one phase-shift compensation layer is always located between the first polarizing layer 1 and the second polarizing layer 2.

[0063] exist Figure 1A In the first technical solution shown and hereinafter referred to as the first alternative or alternative i, a first B* compensation layer 3 is arranged between the first polarizing layer 1 and the second polarizing layer 2. The first B* compensation layer 3 is a spatially uniform layer composed of a biaxial birefringent material. Accordingly, the material or the first B* compensation layer 3 has two optical axes and three principal refractive axes. Each of the three principal refractive axes corresponds to a refractive index n. x n y n zThis is a common characteristic of biaxial birefringent materials. The symbols "x", "y", and "z" correspond to the axes of a Cartesian coordinate system. However, to achieve privacy protection, the principal refractive axis corresponding to either the minimum or maximum refractive index must be parallel to the first absorption axis.

[0064] The orientation of the first absorption axis determines the orientation of all other absorption axes or the principal refractive axes of all types of compensation layers. If the first polarizing layer is, for example, a Z-polarizer, meaning its first absorption axis is parallel to the surface normal or perpendicular to the film surface, then the corresponding principal refractive axis corresponding to the minimum or maximum refractive index is also parallel to the surface normal. Accordingly, the other two principal refractive axes lie in the plane of the optical film surface. In this case, the optical axis of the first B* compensation layer 3, which is a B compensation layer, lies in a plane perpendicular to the optical film surface. In this case, the first B* compensation layer 3 can be constructed in two ways.

[0065] On one hand, it can be constructed as a -B compensation layer. In this case, a Z-polarizer is involved, and therefore, in an imaginary Cartesian coordinate system (where the principal refraction axis and the optical axis of the B* compensation layer are defined), the z-direction is associated with the direction perpendicular to the surface of the optical thin film. In this notation, the -B compensation layer satisfies condition n x >n y >n z Therefore, the minimum refractive index corresponding to the principal axis perpendicular to the surface of the optical thin film is represented by n. z This is indicated. Furthermore, it corresponds to the maximum refractive index n. x The principal refraction axis is parallel to the second absorption axis of the second polarization layer 2.

[0066] On the other hand, it can be constructed as a +B compensation layer. Here, the z-direction can also be associated with a direction perpendicular to the surface of the optical thin film. In this notation, the +B compensation layer satisfies condition n. z >n x >n y Therefore, the maximum refractive index corresponding to the principal axis perpendicular to the surface of the optical thin film is represented by n. z This is indicated by [reference needed]. Furthermore, the principal refractive axis corresponding to the minimum refractive index ny is parallel to the second absorption axis of the second polarization layer 2 (see above).

[0067] Of all the technical solutions in the first alternative, the first B* compensation layer 3 satisfies the condition.

[0068]

[0069] Where d represents the thickness of the first B* compensation layer 3, Δph represents the phase shift caused by the first B* compensation layer, and λ represents the wavelength that is arbitrarily defined in principle to satisfy this condition. This defines the upper limit of the phase delay of the first B* compensation layer 3, and also indirectly defines the maximum thickness.

[0070] exist Figure 1B In the second technical solution, which is shown in the basic structure and is also referred to below as the second alternative or alternative ii, at least two compensation layers made of uniaxial birefringent material are arranged between the first polarization layer 1 and the second polarization layer 2. These are a first A* compensation layer 4 and a second A* compensation layer 5. The two A* compensation layers 4 and 5 are spatially uniformly constructed in a previously defined manner. The first A* compensation layer 4 is made of a first uniaxial birefringent material having a first optical axis and two first principal refractive axes, wherein the first optical axis is perpendicular to or parallel to the first absorption axis of the first polarization layer 1. The second A* compensation layer 5 is arranged rearward from the viewer's perspective, and this compensation layer is made of a second uniaxial birefringent material having a second optical axis and two second principal refractive axes. The orientation of the second optical axis of the second A* compensation layer 5 is determined according to the orientation of the first optical axis of the first A* compensation layer 4, wherein the condition that the second optical axis is perpendicular to the first optical axis must be satisfied. Each of the two A* compensation layers 4 and 5 satisfies the condition.

[0071]

[0072] Where d represents the thickness of the corresponding compensation layer, and n e To represent a special refractive index, n o The value represents the normal refractive index. Δph represents the phase shift caused by the first A* compensation layer or the second A* compensation layer 4 or 5, respectively, and λ represents the wavelength that is arbitrarily specified in principle to satisfy this condition. The two A* compensation layers 4 and 5 can be made of the same material and / or have the same thickness, thereby simplifying the manufacturing process.

[0073] Figure 1C An improved version of the second alternative is shown. To more clearly define the solid angle range—that is, to achieve a greater decrease in luminous density within this range compared to the luminous density outside this range—and / or to achieve greater flexibility in selecting the components of the compensation layer, this second alternative advantageously includes a third C* compensation layer 6 arranged between the first A* compensation layer and the second A* compensation layer, which is also spatially uniform. The third C* compensation layer 6 is composed of a third uniaxial birefringent material having a third optical axis and two third principal refractive axes, wherein the third optical axis is parallel to the first absorption axis of the first polarization layer 1. Here, the orientation of the first absorption axis of the first polarization layer 1 also determines the orientation of the optical axis of the material of the third C* compensation layer 6.

[0074] When the first polarization layer 1 is constructed as a Z-polarizer, and thus the first absorption axis is perpendicular to the surface of the optical thin film, either the first A* compensation layer 4 is constructed as a +A compensation layer and the second A* compensation layer 5 is constructed as a -A compensation layer, or vice versa. When a third C* compensation layer 6 is provided, it is constructed as a -C or +C compensation layer.

[0075] In both the first and second alternatives, the material and thickness d of the compensation layer are specified such that, in a spherical coordinate system with the origin located on the surface of the thin film and in the plane of the thin film, the luminous density is minimized only within a specified solid angle range R. The solid angle range R includes only a portion of the possible perceptible half-space, i.e., it includes, on the one hand, the azimuth angle located on the surface of the thin film. The preferred orientation for measurement is in the plane relative to the film surface. or Less than the specified limit azimuth angle The absolute value. In principle, the preferred direction can be chosen arbitrarily, but should be determined according to the application of the optical film. When such an optical film is applied, for example, to a screen with a fixed orientation (such as in a vehicle), the preferred direction is chosen so that it is parallel to the imaginary line between the eyes of an upright driver, i.e., typically extending horizontally. The limiting azimuth angle is specified according to the intended use of the film. For example, for laptops that need to be protected from being viewed from the side in vehicles such as trains, a common value is 30° to 40° to the left and right of the preferred direction. Here, the preferred direction is usually parallel to the long side of the screen, and the first absorption axis is parallel to the normal of the screen, so that the decrease in light density to all sides is symmetrical.

[0076] On the other hand, the solid angle range for minimum luminous density also includes the polar angle θ, measured relative to the first absorption axis and in the plane formed by the surface normal and the first absorption axis, or measured only relative to the surface normal when the first absorption axis is parallel to the surface normal. The absolute value of this polar angle is greater than the specified limiting polar angle θ. lim Preferably, the limiting polar angle θ lim The angle is 40° to 50°, depending on the application. When this optical film is applied to the screen illustratively described above, it effectively limits the line of sight because the luminous density is minimal within the aforementioned solid angle range. Therefore, ideally, a viewer positioned within the aforementioned solid angle range relative to the spherical coordinate system of the optical film will not perceive any content on the screen, or at least will not be able to recognize it, due to the minimal luminous density within that range.

[0077] Preferably, the line-of-sight limitation effect within a specified solid angle range is achieved by minimizing the luminous density within this solid angle range by coordinating the components of the optical thin film to ensure that the loss function C2 = ∫ within the specified solid angle range R. R The minimum value of ln T(φ, θ)dΩ is found where Let Ω represent the angle-dependent transmittance, and Ω represent the solid angle range. That is, the natural logarithm of the angular-resolved transmittance is calculated and integrated over the solid angle range where privacy protection needs to be optimized. This includes not only the horizontal viewing angle but also the viewing angle deviating from the actual viewer's 0° vertical line of sight (along the surface normal), i.e., upward or downward viewing angles. This also includes, for example, a third viewer standing next to the seated device user in privacy mode. Ultimately, this results in significantly improved privacy protection compared to previous technologies in terms of these viewing angles. Logarithms are used to weight the values ​​on different orders of magnitude, but linear weighting or other weighting methods can also be used.

[0078] Combination Figure 2 and Figure 3 Let me illustrate this point with an example. Figure 2 The projection of a defined solid angle range R onto the optical thin film plane is shown as a black area, also known as a conical image. Within this range, improved privacy protection is needed to minimize the luminous density. In this example, the solid angle range R is defined such that the limiting azimuth angle φ... lim The angle is 40°, thus creating a black area above and below the horizontal axis, and the limiting polar angle θ lim This is also 40° – corresponding to the concave regions to the right and left of the midpoint. In this case, the inner concentric circles correspond to a polar angle of θ = 40°. For this specified range of solid angles, the loss function, i.e., the integral of the logarithmic transmittance, is minimized. The components can be coordinated to meet this condition using the commercially available optical design programs previously illustratively mentioned.

[0079] Ultimately, even for vertical viewing angles other than 0° (corresponding to a perpendicular view of the optical film surface), an improved privacy effect towards the side can be obtained; see [link to documentation]. Figure 3The optical film in the 30° vertical viewing angle and the second alternative has a +A compensation layer and a -A compensation layer on one side, and another -C compensation layer on the other. The first polarization layer 1 is constructed as a Z-polarizer, so that the first absorption axis is parallel to the surface normal of the optical film. The figure shows the privacy effect in arbitrary units, that is, the luminous density normalized to 0° angle according to the horizontal viewing angle in degrees, from which it can be seen how the brightness of the screen is compared with the non-privacy protection angle range. For example, the preferred direction is parallel to the horizontal direction, which is related to the viewer's reference frame, that is, the horizontal direction corresponds to the imaginary connecting line between the viewer's two eyes, and the vertical direction is perpendicular to this. The solid line corresponds to the privacy effect that can be achieved in the prior art using only a Z-polarizer and without a spatially uniform compensation layer at a 30° vertical viewing angle. The dashed line is the privacy effect of the combination of the A* compensation layers of the two types of -A and +A, and the dotted line is the privacy effect of the combination with an additional -C compensation layer. The A* compensation layer in this example is not fully optimized; therefore, the combination with the -C compensation layer does not provide improvement in this example. However, under normal circumstances, using the C* compensation layer can provide improved privacy protection at angles of around 30°. At angles of up to approximately 60°, privacy protection towards the sides is significantly improved. Privacy protection is slightly improved at larger angles greater than 60°, but still an improvement over prior art. This improvement is magnified due to the logarithmic scale, but is not noticeable in practice. At a 0° vertical viewing angle (not shown here), the optical films in the prior art generally have the same results as the optical films described above and below with additional compensation layers, generally corresponding to dashed or dotted lines.

[0080] Figure 2 The solid angle range R shown is merely illustrative and can be adjusted as needed to improve privacy protection for vertical viewing angles, for example, when the horizontal viewing angle is 0°, corresponding to a viewer standing directly behind a seated user on a laptop computer. In this case, for example... Figure 2 The black solid angle range in the image completely surrounds the concentric circle at 40°.

[0081] Figure 4A and 4B , Figure 5A and 5B and Figure 6A and 6B More examples are shown in the figure, where Figure 2 The solid angle range R shown is defined. Figure 4A , Figure 5A and Figure 6A This demonstrates the privacy protection effect at a 0° vertical viewing angle. Figure 4B , Figure 5B and Figure 6BThis demonstrates the privacy protection effect at a 30° vertical viewing angle. Curves with solid lines always correspond to optical films with only a single first Z* polarization layer and no additional spatial uniformity compensation layer.

[0082] Figure 4A and Figure 4B Showing has Figure 1A The privacy protection effect of the optical film of the first alternative structure shown is illustrated, which has a first B* compensation layer 3. For n x n y and n z Multiple combinations of biaxial birefringent layers achieve the same optical function; therefore, such layers are classified by two other parameters that take this point into account, namely, by parameters.

[0083] R e =(n x -n y )·d and parameters

[0084]

[0085] Within the green and mid-visible light wavelength range where the human eye has the highest sensitivity (λ = 550 nm), at a thickness of d = 5.25 μm, Re = 132, and N... z A point-like curve is obtained when n = 3.84. This can be determined from n... x This suggests that there must be a correlation between refractive indices. For example, n x =1.6246, n y =1.6 and n z =1.5287. To manufacture a layer with exactly this calculated refractive index, numerous manufacturing methods for highly controlling the refractive index are known in the prior art. If a material with the desired refractive index ratio is selected, the thickness d is adjusted to satisfy N. z In addition to the aforementioned parameters, other combinations can be used to achieve significant improvements; thus producing the privacy protection characteristics shown by the dashed line, where R e =75 and N z =3.84. This value is for illustrative purposes only; a tolerance of + / -20% may exist in each case and is included without significantly reducing the privacy protection.

[0086] Figure 5A and Figure 5B Showing has Figure 1CThe second alternative structure shown provides privacy protection for the optical film, comprising a first A* compensation layer 4, a second A* compensation layer 5, and an additional third C* compensation layer 6 located between these two layers. The first absorption axis of the first polarizing layer 1 is also perpendicular to this surface, thus constituting a Z-polarizer. Accordingly, the first A* compensation layer 4 is constructed as a +A compensation layer with positive birefringence, the second A* compensation layer 5 is constructed as a -A compensation layer with negative birefringence, and the third C* compensation layer 6 is constructed as a -C compensation layer with negative birefringence. Alternatively, the first A* compensation layer 4 can be constructed as a -A compensation layer with negative birefringence, the second A* compensation layer 5 as a +A compensation layer with positive birefringence, and the third C* compensation layer 6 as a +C compensation layer with negative birefringence, where negative birefringence refers to n... e <n o In the case of positive birefringence, n e >n o The situation.

[0087] At a 0° vertical viewing angle, Figure 5A Corresponding to a direct top view of the film along the surface normal, the use of three additional compensation layers besides the Z-polarizer did not cause any improvement, while at a 30° vertical viewing angle, Figure 5B Then you can clearly see the improved privacy protection effect. Figure 5A and Figure 5B The improvement shown can be achieved using a series of compensation layers, which satisfy the condition d·(n) for the first + A compensation layer. e -n o =264nm, and the second-A compensation layer satisfies the condition d·(n o -n e = -264nm, each with a 20% tolerance. For the third-C compensation layer, condition d·(n) is satisfied. e -n o The tolerance is -22nm, where the tolerance is greater than + / -10nm. For the relatively thin C* compensation layer as a whole, the tolerance is either + / -10nm or 20%, depending on which value is larger. In alternative technologies with a first-A compensation layer, the sign is reversed accordingly.

[0088] Figure 6A and Figure 6B Showing has Figure 1C The second alternative structure shown provides privacy protection for the optical film, which has a first A* compensation layer 4, a second A* compensation layer 5, and an additional third C* compensation layer 6 located between these two layers. Figure 5A , Figure 5BUnlike other polarizing layers, the first absorption axis of the first polarizing layer here is tilted 20° relative to the surface normal, hence it is a Z* polarizer. This orientation also determines how the optical axes of the A* and C* compensation layers should be arranged to achieve the privacy protection effect. To manufacture such tilted compensation layers, for example, the light orientation and polymerization of LC liquid crystal atoms can be used. Without general limitation, the first A* compensation layer 4 is constructed as a -A* compensation layer, the second A* compensation layer 5 is constructed as a +A* compensation layer, and correspondingly, the third C* compensation layer 6 is constructed as a -C* compensation layer. Figure 6A and Figure 6B The improvement shown can be achieved using a series of compensation layers, which satisfy the condition d·(n) for the first +A* compensation layer. e -n o =264nm, for the second -A* compensation layer, the condition d·(n) is satisfied. o -n e = -264nm, each with a 20% tolerance. For the third -C* compensation layer, condition d·(n) is satisfied. e -n o = -82nm, with a tolerance of 20%. In the alternative technology with a first -A* compensation layer, the sign is reversed accordingly.

[0089] exist Figures 7A to 7F In China, with Figure 1C Taking the optical thin film in the second alternative shown as an example, the function of each layer is explained in detail using a polarization ellipse, wherein the first absorption axis of the first polarization layer 1 is parallel to the surface normal of the optical thin film. For comparison, Figure 7G This describes the light polarization when using a layer structure without an additional compensation layer, as described in the prior art. It is assumed that the viewer's line of sight is along the surface normal of the optical thin film. Figures 7A to 7G Each figure shows multiple polarization ellipses circularly distributed around the origin of the coordinate system. The position of each polarization ellipse corresponds to a viewing angle toward the surface of the optical thin film. The viewing angle at the origin of the coordinate system corresponds to the surface normal, i.e., a top view perpendicular to the surface of the optical thin film. Without general limitation, the direction parallel to the shorter side of the plane of the figure relative to the plane is called the x-direction, and the direction perpendicular to it is called the y-direction. The x-direction here also corresponds to the preferred direction and is parallel to the imaginary line connecting the viewer's eyes, and is therefore also referred to as the horizontal direction below. That is to say, in Figures 7A to 7GIn the coordinate system, there are several polarization ellipses on the x-axis, corresponding to viewing angles that deviate from zero only in the horizontal direction, and corresponding to viewers who move away from the origin only in the lateral direction. There are also several polarization ellipses on the y-axis, whose viewing angles deviate from zero only in the vertical direction, corresponding to viewers who move vertically up and down from the origin. "Vertical" movement or displacement here does not mean that the viewer moves away from the optical film along the surface normal; that is, it does not mean displacement along the surface normal within the horizontal plane formed by the surface normal and the viewer's eyes. Rather, it refers to displacement perpendicular to this plane. For example, if a seated first viewer looks directly at the optical film along the surface normal, the viewing angle of a second viewer standing directly behind the first viewer is only vertically offset along the y-axis. For ease of understanding, Figures 7A to 7G Each diagram depicts two concentric circles. The inner circle restricts the maximum angular diameter (GD) in each direction to a maximum of 25°, while the outer circle restricts the maximum GD in each direction to a maximum of 45°. The outermost GD has a GD of 90°, which is imperceptible in reality.

[0090] Figure 7A The diagram shows circularly polarized light emitted by a backlight onto an optical thin film. This light is first incident on a second polarizing layer 2 having a second absorption axis and is linearly polarized because the second absorption axis of the second polarizing layer 2 is oriented parallel to the surface of the thin film, here along a horizontal direction or generally along an imaginary line connecting the viewer's two eyes, which also corresponds to a preferred direction.

[0091] After passing through the second polarization layer, linearly polarized light is incident on the second A* compensation layer 5, which is constructed as a -A compensation layer. Polarization remains almost constant, particularly in the horizontal direction and vertical direction, but over a wider range of viewing angles—in a top view—s-polarized light can be obtained over a larger area after passing through the second polarization layer. See [reference needed]. Figure 7C That is, the vector of the relevant electric field is perpendicular to the incident plane (the plane formed by the surface normal and the incident direction). Figure 7D The angle-resolved polarization is shown after passing through the next layer, namely the third C* compensation layer 6. This compensation layer is constructed as a +C compensation layer here; however, the variation is difficult to see in the figure due to less birefringence and the fact that it is a C* compensation layer. Figure 7E The light is polarized after passing through the first A* compensation layer 4, which is constructed as a +A compensation layer. This light is mostly approximately p-polarized, meaning the vector of the electric field is parallel to the plane of incidence. Therefore, the absorption of light in directions not perpendicular to the propagation direction is increased by the subsequent first polarization layer 1, i.e., the Z-polarization layer. This is achieved through the interaction of the three aforementioned compensation layers. The privacy protection effect is thus significantly enhanced.

[0092] at last, Figure 7F The image shows the polarization of the light after passing through the first polarization layer 1, i.e., the Z-polarizer. For comparison, Figure 7GThe image shows optical polarization in the prior art, where the Z-polarization layer is directly connected to the second polarization layer. The closer the polarization ellipse is to a point shape, the lower the luminous density. This can be clearly seen here. Figure 2 The luminescence density in the black area is much lower than in previous technologies, thus improving the privacy protection effect. This is achieved by minimizing the luminescence density only in the actual part of this half-space outside the narrower viewing cone, as in previous technologies, instead of across the entire half-space. Specifically, the loss function is minimized within the defined solid angle range R.

[0093] C2=∫ R lnT(φ,θ)dΩ

[0094] Minimize, where Here, Ω represents the angle-dependent transmittance, and Ω is the solid angle. This allows for a significant reduction in luminous density within the desired range, thereby improving privacy protection.

[0095] Figure 8 To have similar Figure 1B The optical thin film technology of the first A* compensation layer 4 and the second A* compensation layer 5 is described, but an additional liquid crystal layer 7 is arranged between the second polarization layer 2 and the second A* compensation layer 5, which can switch between at least two states. The liquid crystal layer 7 is constructed such that, in the first switching state, it transmits light transmitted by the second polarization layer 2 with a constant or 90° rotational polarization, and in the second switching state, it transmits light transmitted by the second polarization layer 2 with a circular or elliptical polarization. Of course, the liquid crystal layer 7 using this switching method can also be applied to other optical thin film technologies, especially... Figure 1A and Figure 1C In the technical solution shown.

[0096] Thus, for example, to achieve Figure 10 and Figure 11 The screen shown. Figure 10A screen is shown that can operate in at least two modes, B1 (for free viewing mode) and B2 (for restricted viewing mode), in which light is emitted to a viewing angle that is more limited for the viewer compared to the free viewing mode. To switch between these two modes, the screen includes a backlight 8, which is planar and includes—not specifically shown—an optical film having a liquid crystal layer 7 that can switch between at least two states and emits light, represented here by multiple light sources 9. This is a simplified illustration; for example, a surface emitter or a light guide with structured surface edge illumination could also be used, optionally including optical layers such as a diffuser or prism grating. Alternatively, the backlight can also emit light directly, for example, configured as "Direct Matrix Backlight Dimming". A linear polarizing filter 10 is arranged in front of the backlight 8 along the viewing direction, restricting the propagation direction of light emitted from the backlight 8 and passing through the linear polarizing filter 10. A transmissive image reproduction device 11 is arranged in front of the backlight 8 along the viewing direction. A linear polarizing filter 10 is arranged behind the transmissive image reproduction device 11 along the viewing direction. The polarizing filter should be as close as possible to the image reproduction device, i.e., with as few additional layers as possible between them. Preferably, the linear polarizing filter 10 is arranged in the transmissive image reproduction device 11, i.e., it is part of the latter or integrated into the latter. In operating mode B2, the liquid crystal layer 7, which can switch between at least two states, is in a first switching state; in operating mode B1, the liquid crystal layer 7, which can switch between at least two states, is in a second switching state. That is, the switchable liquid crystal layer enables switching between a common operating mode and a privacy mode. In the common operating mode, the image content displayed on the screen can be viewed without restriction from multiple viewing angles; in the privacy mode, the displayed image content is visible with sufficient brightness only within a narrow viewing angle range around the cone of the first absorption axis of the first polarizing layer 1.

[0097] Figure 11Another technical solution for the screen is shown, which can operate in at least two operating modes, B1 (for free viewing mode) and B2 (for restricted viewing mode), in which light is emitted to a viewing angle that is more limited for the viewer compared to the free viewing mode. The screen includes an image reproduction device 12, which employs the structure disclosed in the prior art and can be constructed, for example, as an actively emitting image reproduction device 12 based on OLED or microLED, or as a passively emitting (i.e., illuminated) image reproduction device 12 based on, for example, LCD. An optical film is arranged in front of the image reproduction device 12 along the viewing direction, having a liquid crystal layer 7 that can be switched between at least two states. This optical film is constructed, for example, according to a first alternative, wherein a spatially uniform first B* compensation layer 3 made of a biaxial birefringent material is arranged between the first polarization layer 1 and the second polarization layer 2. The second polarization layer 2 can also be constructed, for example, as a rear polarizer of the LC display of the image reproduction device 12. Of course, all other aforementioned technical solutions with an optical film having a switchable liquid crystal layer 7 can also be employed. Similar to the aforementioned screen, the liquid crystal layer 7, which can switch between at least two states, is in the first switching state in operating mode B2 and in the second switching state in operating mode B1. This technical solution is particularly suitable for retrofitting existing screens.

[0098] Alternatively, an optical film without the switchable liquid crystal layer 7 can be used to manufacture an illumination device for the screen, which can be configured to operate in at least two operating modes B1 (for free viewing mode) and B2 (for restricted viewing mode), in which light is emitted to a more limited solid angle range compared to the free viewing mode. Figure 9A and Figure 9B Examples of this type of lighting device in these two operating modes are shown. If the lighting device is combined with an image reproduction device located upstream along the viewing direction for displaying image content, a screen that can be switched between these two operating modes B1 and B2 can be obtained.

[0099] Figure 9A and Figure 9B The lighting device shown includes a planar extended backlight 13, in which an integrated... Figures 1A to 1CAn illustrative example is a static, i.e., non-switchable, optical film. A plate-shaped light guide 14 is arranged in front of the backlight 13 along the viewing direction, having an output coupling element on at least one of its large surfaces and / or within its volume. In the illustrated example, the output coupling element 15 is arranged within the volume of the light guide 14. A linear polarizing filter 16 is arranged in front of the backlight 13 or the light guide 14 along the viewing direction. This, in principle, restricts the propagation direction of light emitted from the backlight 13, penetrating the optical film, and then penetrating the linear polarizing filter 16. Optionally, the linear polarizing filter 16 may also function as a second polarizing layer 2, i.e., equivalently. A light-emitting member 17 is laterally arranged on at least one narrow side of the light guide 14—here, on both narrow sides—which, in the on state, directs light into the light guide 14. The light incident on the light-emitting component 17 is reflected back and forth in the light guide 14 by total internal reflection until it is incident on the output coupling element 15. This output coupling element deflects the light, causing it to pass through the surface of the light guide 14 and illuminate the viewer outward. The output coupling element 15 is configured to deflect the light almost completely in this direction, allowing the light originating from the backlight 13 to pass through almost unobstructed.

[0100] Figure 9A The lighting device is shown in operating mode B2 for a restricted viewing mode, in which only a small, typically conical solid angle range is illuminated, indicated by an arrow on the surface of the light guide 14. In this case, only the backlight 13 is turned on, and the light-emitting component 17 must be turned off. Figure 9B The lighting arrangement is shown in operating mode B1 for public viewing, where light is emitted over a much larger or wider solid angle range compared to operating mode B2, also indicated by arrows on the light guide 14. In this case, the light-emitting element 17 must be switched on, and the light emitted into the light guide 14 and coupled by the output coupling element 15 is used to widen the illuminated solid angle range. The backlight 13 can be switched on or off in operating mode B1. When the backlight 13 is switched off, uniform illumination of the solid angle range is typically achieved in operating mode B1.

[0101] Through Figure 9A and Figure 9B The passive image reproduction device, which is illuminated from the rear, generates a restricted viewing mode B2 or a public viewing mode B1 for viewers of the image content displayed on the image reproduction device, depending on whether the light-emitting component 17 is turned on or off.

[0102] With the aid of an image reproduction device and, if necessary, a dedicated lighting device, the aforementioned optical film can be widely applied to any situation requiring the display and / or input of confidential information, such as PIN entry, data display on ATMs or payment terminals, password input, or reading emails on mobile devices. This invention can also be applied, in particular, to motor vehicles to selectively block interfering image content for the driver or passengers.

[0103] [Symbol Explanation]

[0104] 1: First polarization layer

[0105] 2: Second polarization layer

[0106] 3: First B* Compensation Layer

[0107] 4: First A* Compensation Layer

[0108] 5: Second A* Compensation Layer

[0109] 6: Third C* Compensation Layer

[0110] 7: Liquid Crystal Layer

[0111] 8: Backlight

[0112] 9: Light source

[0113] 10: Linear polarizing filter

[0114] 11: Image Reproduction Device

[0115] 12: Image Reproduction Device

[0116] 13: Backlight

[0117] 14: Light guide

[0118] 15: Output coupling element

[0119] 16: Linear polarizing filter

[0120] 17: Light-emitting components

[0121] R: Solid angle range

Claims

1. Backlight (13) which is planar, emits light and has an optical film for controlling and limiting the viewing angle range of a viewer, which comprises a first polarizing layer (1) with a first absorption axis which forms an angle of 0° to 30° with the surface normal of the optical film, at least one phase shift compensation layer for improving the limitation of the viewing angle range, and a second polarizing layer (2) with a second absorption axis which is parallel to the surface of the optical film, between the first polarizing layer (1) and the second polarizing layer (2), in a first alternative solution i. a first B* compensation layer (3) is arranged which is spatially uniform and consists of a first biaxial birefringent material which has two optical axes and three principal refractive axes, wherein the principal refractive axis corresponding to the minimum refractive index or the principal refractive axis corresponding to the maximum refractive index is parallel to the first absorption axis, and wherein for the first B* compensation layer (3) the condition is fulfilled d * Δph < 2 * λ, comprising the thickness d, the phase shift Δph and a defined wavelength λ, in a second alternative solution ii. at least two compensation layers consisting of uniaxial birefringent materials are arranged, wherein a first "A*" compensation layer (4) which is spatially uniform consists of a first uniaxial birefringent material which has a first optical axis and two first principal refractive axes which are different from each other, wherein the first optical axis is perpendicular or parallel to the first absorption axis of the first polarizing layer (1) and viewed behind from the viewer direction, a second "A*" compensation layer (5) which is spatially uniform is arranged which consists of a second uniaxial birefringent material which has a second optical axis and two second principal refractive axes, wherein the second optical axis is perpendicular to the first optical axis, wherein each of the compensation layers fulfils the condition d * Δph < 2 * λ, comprising the thickness d, the phase shift Δph and a defined wavelength λ, between the first "A*" compensation layer and the second "A*" compensation layer a third "C*" compensation layer (6) which is spatially uniform is arranged which consists of a third uniaxial birefringent material which has a third optical axis and two third principal refractive axes, wherein the third optical axis is parallel to the first absorption axis of the first polarizing layer (1). The first absorption axis is perpendicular to the surface of the film. The first "A*" compensation layer (4) is constructed as a "+A" compensation layer, the second "A*" compensation layer (5) is constructed as a "-A" compensation layer, or vice versa, and, in the case of a third "C*" compensation layer (6) being provided, the compensation layer is constructed as a "-C" or "+C" compensation layer. The first "A*" compensation layer (4) and the second "A*" compensation layer (5) are of identical construction. characterized in that Between the second polarizing layer (2) and the compensation layer which is closest to the second polarizing layer a liquid crystal layer (7) is arranged which can be switched between at least two states, which is constructed such that in a first switching state it transmits the light transmitted by the second polarizing layer (2) with unaltered or 90° rotated polarization, and in a second switching state it transmits the light circularly or elliptically or linearly polarized. ​ wherein each of the principal refractive axes corresponds one by one to a refractive index n x , n y , n z , ​ ​ ， ​ ​ ​ ​ ​ ， The thickness d, the specific refractive index n e and the normal refractive index n o , the phase shift Δph and the prescribed wavelength λ, and wherein in both said alternatives i and ii the material and thickness d of the compensating layer are specified such that the luminous density is minimum only within a specified solid angle range R, measured in a spherical coordinate system with the origin at the surface of the film and the plane of the surface of the film, said solid angle range comprising: an azimuthal angle φ, wherein the absolute value of |φ| and |180° - φ| is less than a specified limit azimuthal angle φ lim ; and a polar angle θ, measured with respect to the surface normal, or with respect to the first absorption axis when the first absorption axis is not parallel to the surface normal and in the plane formed by the surface normal and the first absorption axis, the absolute value of said polar angle being greater than a specified limit polar angle θ lim .

2. The backlight (13) according to solution ii in claim 1, wherein ​ 3. The backlight (13) according to claim 1 or 2, wherein ​ 4. The backlight (13) according to claim 3 alternative i, wherein said principal refractive axis corresponding to the minimum refractive index is parallel to said first absorption axis, characterized in that said first "B*" compensation layer (3) is constructed as a "-B" compensation layer, wherein n x n y n z said principal refractive axis corresponding to the minimum refractive index n z is parallel to said surface normal, said principal refractive axis corresponding to the maximum refractive index n x is parallel to a second absorption axis of said second polarizing layer (2).

5. The backlight (13) according to claim 3 alternative i, wherein, said principal refractive axis corresponding to the maximum refractive index is parallel to said first absorption axis, characterized in that said first "B*" compensation layer (3) is constructed as a "+B" compensation layer, wherein n z n x n y said principal refractive axis corresponding to the maximum refractive index n z is parallel to said surface normal, said principal refractive axis corresponding to the minimum refractive index n y is parallel to a second absorption axis of said second polarizing layer (2).

6. The backlight (13) according to claim 3 alternative ii, wherein ​ 7. The backlight (13) according to claim 1 alternative ii, wherein, ​ 8. The backlight (13) according to claim 1 or 2, wherein, ​ 9. The backlight (13) according to claim 1 or 2, wherein, Between the first polarizing layer (1) and the compensation layer closest to the first polarizing layer there is arranged a liquid crystal layer (7) which is switchable between at least two states, which is constructed in such a way that in a first switching state it transmits the light transmitted by the first polarizing layer (1) with unaltered or 90°-rotated polarization, and in a second switching state it transmits the light circularly or elliptically or linearly polarized.

10. The backlight (13) according to claim 1 or 2, wherein, loss function within the prescribed solid angle range R is minimized, where denotes the angle-dependent transmittance, and Ω denotes the solid angle range.

11. The backlight (13) according to claim 1 or 2, wherein, said limit azimuth φ lim between 30° and 40° to the preferred direction and / or said limit polar angle θ lim between 40° and 50°.

12. An illumination device for a screen, the illumination device being configured such that it can be operated in at least two modes of operation B1 and B2, wherein, B1 is for a free viewing mode, and B2 is for a restricted viewing mode in which light is emitted into a more limited solid angle than in the free viewing mode, the illumination device comprising The backlight (13) according to any one of claims 1 to 7, 10 or 11, A plate-shaped light guide (14) which is arranged in front of the backlight (13) in the viewing direction, which light guide has output coupling elements (15) on at least one of its large surfaces and / or within its volume, A light emitting means (17) which is arranged laterally on at least one narrow side of the light guide (14), and A linear polarization filter (16) which is arranged in front of the backlight (13) or in front of the light guide in the viewing direction, such that light which is emitted from the backlight (13) and which penetrates the linear polarization filter (16) is limited in its propagation direction, wherein in the operating mode B2 the backlight (13) is switched on, the light emitting means (17) is switched off, and wherein in the operating mode B1 at least the light emitting means (17) is switched on.

13. A screen, which is operable in at least two modes of operation B1 and B2, wherein, B1 is for a free viewing mode, and B2 is for a restricted viewing mode in which light is emitted into a more limited viewing angle range for the viewer than in the free viewing mode, the screen comprising The backlight (8) according to claim 8 or 9, having a liquid crystal layer (7) which is switchable between at least two states, A linear polarization filter (10) which is arranged in front of the backlight (8) in the viewing direction, such that light which is emitted from the backlight (8) and which penetrates the linear polarization filter (10) is limited in its propagation direction, and A transmissive image reproduction device (11) which is arranged in front of the backlight (8) in the viewing direction, the linear polarization filter (10) being arranged in or behind the image reproduction device, wherein in the operating mode B2 the liquid crystal layer (7) which is switchable between at least two states is in a first switching state, and wherein in the operating mode B1 the liquid crystal layer (7) which is switchable between at least two states is in a second switching state.

14. A screen, which is operable in at least two modes of operation B1 and B2, wherein, B1 is for a free viewing mode, and B2 is for a restricted viewing mode in which light is emitted into a more limited viewing angle range for the viewer than in the free viewing mode, the screen comprising An image reproduction device (12), An optical film which is arranged in front of the image reproduction device (12) in the viewing direction, the optical film having a liquid crystal layer (7) which is switchable between at least two states, wherein in the working mode B2 the liquid crystal layer (7) is in a first switching state, and wherein in the working mode B1 the liquid crystal layer (7) is in a second switching state, The optical film comprises: a first polarizing layer (1) having a first absorption axis, which forms an angle of 0° to 30° with the surface normal of the optical film; at least one phase shift compensation layer for improving the limitation of the viewing angle range; and a second polarizing layer (2) having a second absorption axis, which is parallel to the surface of the optical film, wherein, between the first polarizing layer (1) and the second polarizing layer (2), in the first alternative i. a first B* compensation layer (3) is arranged, which is spatially uniform and composed of a first biaxial birefringent material having two optical axes and three principal refractive axes, wherein each of the principal refractive axes corresponds one by one to a refractive index n x , n y , n z , wherein the principal refractive axis corresponding to the minimum refractive index or the principal refractive axis corresponding to the maximum refractive index is parallel to the first absorption axis, and wherein the first B* compensation layer (3) satisfies the condition ， the thickness d, the phase shift Δph and the specified wavelength λ of the first B* compensation layer (3), ii. in the second alternative, at least two compensation layers composed of uniaxial birefringent materials are arranged, wherein a spatially uniform first "A*" compensation layer (4) is composed of a first uniaxial birefringent material having a first optical axis and two first principal refractive axes different from each other, wherein the first optical axis is perpendicular or parallel to the first absorption axis of the first polarizing layer (1), and viewed from the viewer direction behind a spatially uniform second "A*" compensation layer (5) is arranged, which is composed of a second uniaxial birefringent material having a second optical axis and two second principal refractive axes, wherein the second optical axis is perpendicular to the first optical axis, wherein each of the compensation layers satisfies the condition ， The thickness d, the specific refractive index n e and the normal refractive index n o , the phase shift Δph and the prescribed wavelength λ, wherein in said alternatives i and ii, the material and thickness d of the compensating layer are specified such that the luminous density is minimum only within a specified solid angle range R, measured in a spherical coordinate system with the origin at the surface of the film and the plane of the surface of the film, said solid angle range comprising: an azimuthal angle φ, wherein the absolute value of |φ| and |180° - φ| is less than a specified limit azimuthal angle φ lim measured with respect to a preferred direction in the plane of the surface of the film, and a polar angle θ, measured with respect to the surface normal, or, when the first absorption axis is not parallel to the surface normal, with respect to the first absorption axis and the plane formed by the surface normal and the first absorption axis, and the absolute value of said polar angle is greater than a specified limit polar angle θ lim ​ and wherein between the second polarizing layer (2) and the compensation layer closest to the second polarizing layer, a liquid crystal layer (7) capable of switching between at least two states is arranged, which is constructed to transmit the light transmitted by the second polarizing layer (2) in a polarization unchanged or rotated by 90° in a first switching state, and to transmit the light in a circular or elliptical or linear polarization in a second switching state, or, between the first polarizing layer (1) and the compensation layer closest to the first polarizing layer, a liquid crystal layer (7) capable of switching between at least two states is arranged, which is constructed to transmit the light transmitted by the first polarizing layer (1) in a polarization unchanged or rotated by 90° in a first switching state, and to transmit the light in a circular or elliptical or linear polarization in a second switching state.

15. The screen according to claim 14 alternative ii, wherein, between the first "A*" compensation layer and the second "A*" compensation layer, a spatially uniform third "C*" compensation layer (6) is arranged, which is composed of a third uniaxial birefringent material having a third optical axis and two third principal refractive axes, wherein the third optical axis is parallel to the first absorption axis of the first polarizing layer (1).

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