Backlighting, a device for illuminating a screen, screens, and optical film to control and restrict the viewing angle range of an observer.

Abstract

The invention relates to a backlighting (13) which extends in a flat manner, emits light, and has an optical film in order to monitor and limit the viewing angle range of a viewer. When viewed in the direction of a viewer, the optical film comprises a first polarization layer (1) with a first absorption axis, which forms an angle of 0° to 30° together with a surface normal of the optical film, at least one phase-shifting compensation layer for improving the limitation of the viewing angle range, and a second polarization layer (2) with a second absorption axis, which is oriented parallel to the surface of the optical film. According to the invention, different embodiments and combinations of compensation layers which are designed to be spatially homogenous and which are made of uniaxially or biaxially birefringent materials are provided, wherein the materials and thickness of the compensation layers are specified such that the luminance is minimal in a specified solid angle range which does not comprise the entire half space, apart from a recessed cone along the viewing direction.

Description

1 / 43 “BACKLIGHTING, ILLUMINATION DEVICE FOR A SCREEN, SCREENS AND OPTICAL FILM FOR CONTROLLING AND RESTRICTING THE VIEWING ANGLE RANGE OF AN OBSERVER” Technical Field

[001] This disclosure relates to a planar, light-emitting backlight that includes an optical film for controlling and restricting the observer's viewing angle range. This disclosure also relates to an optical film. The film includes a first polarization layer with a first absorption axis, which is oriented at an angle of 0° to 30° with respect to the normal to the surface of the optical film, and a second polarization layer with a second absorption axis, which is oriented parallel to the surface of the optical film. At least one phase-shift compensation layer to improve the restriction of the viewing angle range is provided between the first polarization layer and the second polarization layer. Viewed from the observer's direction, the first or second polarization layer may be formed as the layer closest to the observer.

[002] In recent years, there has been great progress in widening the viewing angle range on LCDs. However, there are often situations where this wide viewing angle of a screen can be disadvantageous. Increasingly, information such as bank details or other personal and confidential data is also becoming available on mobile devices such as laptops and tablets. Consequently, people need to control who can see this confidential data. They need to be able to choose a wide viewing angle range or a wide viewing angle in a public mode – to share information on their screen with others, for example, when viewing vacation photos or for advertising purposes. On the other hand, they need a narrow viewing angle range or a Petition 870250080945, dated 09 / 09 / 2025, page 70 / 132 2 / 43 small viewing angle in a private mode if you want to handle image information confidentially.

[003] A similar problem arises in vehicle construction: when starting the engine, the driver must not be distracted by image content, such as digital entertainment programs, while the passenger wishes to consume these images while driving. Therefore, a screen is needed that can switch between the respective display modes.

[004] Additional films based on microlaminated sheets have already been applied to mobile displays to ensure visual protection of data. However, these films were not interchangeable, needing to be applied manually first and then removed. Furthermore, they had to be transported separately from the display if not needed. A substantial disadvantage of such laminated sheet films is also associated with light loss. Background of the Invention

[005] US patent 6,765,550 (B2) describes this privacy protection achieved through microlaminated sheets. The biggest disadvantage here is the mechanical removal or mechanical attachment of a filter and the loss of light in protected mode.

[006] US patent 5,993,940 A describes a film with small prisms in the form of strips arranged uniformly on its surface to achieve a private mode, that is, a restricted viewing mode with a small viewing angle. The technical difficulty in research, development and production is quite high.

[007] In document WO 2012 / 033583 A1, the switching between a clear field of view and a restricted field of view is performed by means of a liquid crystal control between the so-called “chromonic” layers. This results in light loss and very high technical complexity. Petition 870250080945, dated 09 / 09 / 2025, page 71 / 132 3 / 43

[008] US patent 2012 / 0235891 A1 describes a very complex backlighting system in a display. According to Figures 1 and 15, not only are a plurality of light guides applied, but also other complex optical elements, such as microlens elements (40) and prism structures (50), which convert the light from a backlight into a path for a frontlight. This is expensive and technically complex to implement, and is associated with light loss. According to a variant of Figure 17 in US patent 2012 / 0235891 A1, both light sources (4R and 18) produce light with a narrow illumination angle, with the light from the backlight source (18) being converted into light with a wide illumination angle in a complex manner. This complex conversion, as already mentioned, significantly reduces brightness.

[009] According to document JP 2007-155783 A, special optical surfaces (19), complex to calculate and produce, are applied, which then deflect light into different narrow or wide bands, depending on the angle of incidence of the light. These structures are similar to Fresnel lenses. In addition, there are interference flanks that deflect light in undesirable directions. Therefore, it is not yet clear whether truly reasonable light distributions can be achieved.

[0010] US patent 2013 / 0308185 A1 describes a special light guide, formed by steps, that emits light onto a large surface in different directions, in particular depending on the direction from which the light guide is illuminated from a narrow side. In cooperation with a transmissive image reproduction device, for example, an LCD display, it is possible to generate a screen switchable between free and restricted viewing modes. A disadvantage here is that the restricted visual effect can only be generated left / right or up / down, but not simultaneously left / right / up / down, as is necessary for certain processes. Petition 870250080945, dated 09 / 09 / 2025, p. 72 / 132 4 / 43 of payment. Additionally, in restricted display mode, residual light is still visible at blocked viewing angles.

[0011] Applicant's WO 2015 / 121398 A1 document describes a screen with two operating modes, in which scattering particles are present in a corresponding light guide volume to switch between operating modes. However, scattering particles selected from a polymer generally have the disadvantage that light is emitted and coupled from two large surfaces, causing approximately half of the useful light to be emitted in the wrong direction, i.e., in the direction of the backlight, and it cannot be recycled to a sufficient extent due to the structure. Furthermore, polymer scattering particles distributed in the light guide volume can, under certain circumstances, especially at higher concentrations, lead to scattering effects that reduce the privacy protection effect in the protected operating mode.

[0012] One approach to “electrical birefringence (EDB)” technology is based on the concept of using switchable liquid crystals in an additionally applied LC panel to “filter” all light beams that do not emerge from an image layer at a specific emission angle. The disadvantages of this technology are high energy consumption and high cost, as well as the difficulty in altering the + / -40° sweet spot, i.e., the best viewing position. The absorbance of LC structures is also insufficient, as the attenuation of light intensity increases again for viewing angles greater than the sweet spot, so that the light intensity for viewing angles greater than + / -40° is at most 3% of the maximum light intensity.

[0013] US patent 2019 / 0094626 A1 describes an optical layer structure for controlling or restricting a viewing angle, in which two Petition 870250080945, dated 09 / 09 / 2025, p. 73 / 132 5 / 43 phase-difference plates are arranged as compensation layers in a linear polarizer. The two phase-difference plates are A / 4 plates with optically anisotropic structured layers in the form of fins or strips, between which a support material may be placed. The layers may have the same construction but differ in their orientation in the final arrangement. The top layer is formed as a polarization layer, in which an absorption axis of a transition dipole moment responsible for polarization is oriented in a direction perpendicular to a surface of the layer, also called the "Z polarizer". In the case of a finned structured layer, there is always the possibility of visual artifacts, such as Mohr stripes, occurring, so such layers can only be adopted for screens whose characteristics, such as resolution and dimensions, apertures, scattering properties, distance to the screen surface, etc.These standards are known, but they cannot be universally adopted regardless of screen size.

[0014] The methods and arrangements mentioned above generally present disadvantages, such as the significant reduction in the brightness of the base screen and / or the need for a complex and expensive optical element for mode switching and / or the reduction in resolution in public mode for free viewing and / or the presence of visual artifacts on a screen with very high resolution. Another disadvantage is that the viewing angle range is not completely restricted; image content with significantly reduced brightness can sometimes be recognized, even though the viewing angle range should be restricted, which has an adverse effect, for example, during night driving of a motor vehicle. Brief Description of the Invention

[0015] The objective of this disclosure is to develop a backlight with an optical film to control and restrict a range of Petition 870250080945, dated 09 / 09 / 2025, page 74 / 132 6 / 43 viewing angle of an observer looking at the film, which is usually combined with a screen, thus improving the restriction of the viewing angle range and making it more difficult for unauthorized users to spy on protected image content, i.e., to further enhance the so-called privacy effect.

[0016] For the optical film with the layered structure mentioned above and the backlighting with such optical film, a solution adopted by the present disclosure to achieve the above objective is a special technical solution of at least one compensation layer, in which a first polarization layer and a second polarization layer will be described in detail initially. The first polarization layer has a first absorption axis, which is located at an angle of 0° to 30° relative to the normal of the optical film surface. When the angle is 0°, that is, when the absorption axis is parallel to the surface normal or perpendicular to the film surface, the first polarization layer is called a “Z polarizer”. When the angle is different and is within the mentioned range of up to 30°, the first polarization layer is also called a “Z* polarizer” hereafter.The absorption of the first polarization layer is generally static, but switchable schemes can be adopted so that angle-dependent absorption can be switched on and off. The second polarization layer has a second absorption axis parallel to the surface of the optical film. Therefore, the second polarizer is a conventional linear polarizer. At least one phase-shift compensation layer is placed between the first and second polarization layers to improve the restriction of the viewing angle range. Both the first and second polarization layers can be closer to the observer. Preferably, all layers are fixed and connected, for example, by junction. Petition 870250080945, dated 09 / 09 / 2025, page 75 / 132 7 / 43 of materials, welding or optical bonding.

[0017] For ease of understanding, it is generally assumed that, in the Cartesian coordinate system composed of the x, y, and z directions, the surface of the film is located in a plane parallel to the xy plane formed by the x and y directions. Therefore, the normal to the surface is parallel to the z direction.

[0018] To improve the privacy effect, i.e., to improve the restriction of the viewing angle range, in principle, two ways can be adopted to construct at least one phase-shift compensation layer. In a first alternative – hereinafter also known as alternative i – a first compensation layer (B*) is arranged between the first polarization layer and the second polarization layer, which is made of a first biaxially birefringent material. The biaxially birefringent material has two principal optical axes and three principal refraction axes, which are in one-to-one correspondence with the refractive indices nx, ny and nz, respectively.Depending on the technical solution of the first compensation layer (B*) and the orientation of its optical axis, the principal refraction axis corresponding to the minimum refractive index or the principal refraction axis corresponding to the maximum refractive index is parallel to the first absorption axis. For the first compensation layer (B*), one condition: The condition Δph = yd |nx— ny| < 2π (1) is satisfied, where d represents the thickness of the first compensation layer, Δph represents a phase shift caused by the first compensation layer (B*), and λ represents any wavelength specified in principle that satisfies this condition. Thus, an upper limit for the phase lag of the first compensation layer (B*) is defined, and the Petition 870250080945, dated 09 / 09 / 2025, page 76 / 132 The maximum thickness of 8 / 43 is also specified indirectly.

[0019] In a second alternative – hereinafter also referred to as alternative ii – at least two compensation layers made of uniaxially birefringent materials are arranged between the first polarization layer and the second polarization layer, wherein a first compensation layer (A*) formed to be spatially homogeneous is made of a first uniaxially birefringent material having a first optical axis and two first principal refraction axes that are different from each other, and the first optical axis that coincides with one of the first principal refraction axes is perpendicular or parallel to the first absorption axis of the first polarization layer.When viewed from the direction of an observer, a second compensation layer (A*) formed to be spatially homogeneous is arranged behind it, which is made of a second uniaxial birefringent material having a second optical axis and two second principal refraction axes, wherein the second optical axis of the second material that coincides with one of the second principal refraction axes is perpendicular to the first optical axis of the first material. The optical axes of these uniaxial materials are also called special axes.

[0020] The term “spatially homogeneous” here means that the corresponding compensation layer is not structured within itself or in an area parallel to the surface of the optical film and therefore has the same property throughout the area, which differs, for example, from US document 2019 / 0094626 A1. To avoid visual artifacts in this type of sheet-structured layer, according to a technical solution in US document 2019 / 0094626 A1, the layer structure must be specifically adjusted for each configuration in terms of resolution, distance, aperture, surface, and scattering characteristics, which increases manufacturing costs. The optical film of the present disclosure with the layer of Petition 870250080945, dated 09 / 09 / 2025, page 77 / 132 9 / 43 compensation, designed to be spatially homogeneous, can be widely adopted on screens of various sizes and resolutions without special adjustments.

[0021] For each of these two compensation layers (A*), a condition: kph = yd |ne-n0| < 2π (2) is satisfied, where d represents a thickness of a respective compensation layer (A*), ne represents an extraordinary refractive index and no represents a normal refractive index, Δρή represents a phase change caused by the first compensation layer (A*) or the second compensation layer (A*), and λ represents any specified wavelength that satisfies this condition.

[0022] In these two alternatives, the materials and thicknesses of the compensation layers are specified so that a luminance density is minimal only within a specified range of solid angles (R) in a spherical coordinate system with its origin located on a surface and on a plane of the film. The range of solid angles (R) includes only a portion of a possible perceptible halfspace, that is, on one hand, it includes an azimuth φ. When measured in a preferred direction in the plane where the film surface is located, |φ| or |180°φ| is less than an absolute value of a specified limit azimuth φπη. In principle, the preferred direction can be selected arbitrarily, but it must be selected according to the applied optical film.When applying optical film to a screen with a fixed orientation (for example, in a vehicle), the preferred orientation is selected so that it is parallel to an imaginary line between the eyes of an upright driver, i.e., it generally extends horizontally. Petition 870250080945, dated 09 / 09 / 2025, page 78 / 132 10 / 43

[0023] On the other hand, the range of solid angles with minimum luminance density also includes a polar angle θ. When measured relative to the first absorption axis and in a plane formed by the surface normal and the first absorption axis (whose vectors have a common origin), an absolute value of the polar angle is greater than a specified limiting polar angle Olm, i.e., all solid angles, except a cone with the limiting polar angle θlim, are present around the first absorption axis (here called the “zero axis”). With the surface normal parallel to the first absorption axis, the polar angle is measured only relative to the surface normal. When applied to the screen illustrated above in an exemplary manner, the optical film effectively restricts vision, since the luminance density is minimal within the range of solid angles described above.Therefore, in an ideal situation, an observer positioned within the aforementioned range of solid angles relative to the spherical coordinate system of the optical film will not perceive anything on the screen due to the minimum luminance density within the range. The term "minimum luminance density" refers to a luminance density of approximately zero, where the luminance density drops significantly compared to the luminance density outside the range of solid angles described above, making the observer unable to see any image content in an ideal situation.

[0024] To define the solid angle range more clearly, i.e., to obtain a greater decrease in luminance density internally compared to the luminous density outside the solid angle range, in the second alternative ii, advantageously, a third compensation layer (C*) formed to be spatially homogeneous is disposed between the first compensation layer (A*) and the second compensation layer (A*), which is made of a third uniaxially birefringent material having a third optical axis and two third principal refractive axes, where the third optical axis is Petition 870250080945, dated 09 / 09 / 2025, page 79 / 132 11 / 43 parallel to the first absorption axis of the first polarization layer.

[0025] To obtain a symmetrical decrease in luminance density relative to the film surface, the first absorption axis is perpendicular to the film surface. In the case of the optical film applied to the aforementioned screen, the observer looking at the screen along the normal to the screen surface perceives a symmetrical decrease in luminance density depending on a change in the viewing angle to the right or left or in the preferred direction, i.e., only relative to the absolute value of the polar angle. In this case, the limiting polar angle θιim is measured relative to the surface normal, therefore it is the same for all azimuths, which is different from the measurement relative to the first absorption axis.

[0026] When the first absorption axis is oriented in the manner described above, the first polarization layer is also called the (Z) polarization layer. When the first absorption axis is oriented differently in the aforementioned band, the first polarization layer is called the (Z*) polarization layer, i.e., the symbol “*” used here indicates a generalization of the (Z) polarization layer.

[0027] Similarly, the compensation layer term (A*) indicates the generalization of the compensation layer term (A), and the compensation layer term (B*) indicates the generalization of the compensation layer term (B). To define the terms “polarization layer (Z)”, “compensation layer (A)” and “compensation layer (B)” known in the state of the art, 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”, published online in Optical Materials 99 (2020), Ref. 109531.

[0028] When the first absorption axis is perpendicular to the surface of the film, that is, the first polarization layer is built Petition 870250080945, dated 09 / 09 / 2025, page 80 / 132 12 / 43 as the polarization layer (Z), multiple beneficial technical solutions are generated, among which two technical solutions are made for the first alternative and a third technical solution is made for the second alternative. The orientation of the optical axis of the compensation layer should, in principle, correspond to the orientation of the first absorption axis of the first polarization layer to achieve a desired restricted viewing area. For example, in a situation where the observer, such as a vehicle driver, is looking at the screen not along the surface normal but at an oblique angle, the first absorption axis may preferably have a different orientation.

[0029] In a first technical solution based on the first alternative, the first absorption axis of the first polarization layer is perpendicular to the surface of the optical film and the principal refraction axis corresponding to the minimum refractive index is parallel to the first absorption axis, in which the first compensation layer (B*) is constructed as the compensation layer (-B). The optical axis is located in the plane formed by the x and z directions, and these three principal refraction axes correspond to the respective directions of the Cartesian coordinate system, where nx > ny > nz, and nx is parallel to the second absorption axis of the second polarization layer.This last condition also applies to a smaller tilt angle, where the first absorption axis is tilted up to about 10° relative to the surface normal; otherwise, the principal refractive axis will be tilted, and the orientation of the coordinate system in the x, y, and z directions is based on the orientation of the first absorption axis, which corresponds to the z direction of the coordinate system, where the essence is that nx is perpendicular to the first absorption axis.

[0030] In a second technical solution based on the first alternative, the first absorption axis of the first polarization layer is Petition 870250080945, dated 09 / 09 / 2025, page 81 / 132 13 / 43 perpendicular to the surface of the optical film and the principal refraction axis corresponding to the maximum refractive index is parallel to the first absorption axis, in which the first compensation layer (B*) is constructed as the compensation layer (+B). The optical axis is located in the plane formed by the yez directions, and the three principal refraction axes correspond to the respective directions of the Cartesian coordinate system, where nz > nx > ny, and ny is parallel to the second absorption axis of the second polarization layer.This last condition also applies to a smaller tilt angle, where the first absorption axis is tilted up to about 10° relative to the surface normal; otherwise, the principal refractive axis will be tilted, and the orientation of the coordinate system in the x, y, and z directions is based on the orientation of the first absorption axis, which corresponds to the z direction of the coordinate system, where the essence is that ny is perpendicular to the first absorption axis.

[0031] In a third technical solution based on the second alternative, the first absorption axis of the first polarization layer (1) is also perpendicular to the surface of the optical film, in which the first compensation layer (A*) is constructed as compensation layer (+A), and the second compensation layer (A*) is constructed as compensation layer (-A), or vice versa. When a third compensation layer (C*) is provided, it is constructed as compensation layer (-C) or (+C).

[0032] To keep manufacturing costs low, preferably, the first compensation layer (A*) and the second compensation layer (A*) have the same structure, i.e., the two compensation layers are constructed as compensation layers (+A) or compensation layers (-A) and have the same thickness.

[0033] In all the technical solutions mentioned, according Petition 870250080945, dated 09 / 09 / 2025, page 82 / 132 14 / 43 With a particularly preferred solution, the liquid crystal layer, which can be switched between at least two states, is arranged between the second polarization layer and the compensation layer closest to the second polarization layer. The liquid crystal layer is constructed to transmit the light transmitted by the second polarization layer with an unchanged polarization or a linear polarization rotated by 90° in a first switching state, and to transmit the light with a circular, elliptical, or linear polarization in a second switching state. In the first switching state, a 90° rotation means that linearly polarized light enters the switchable liquid crystal layer and becomes linearly or elliptically polarized light, where most of the vectors of an electric field rotate by 90°. In other words, it does not mean that the polarization is rotated exactly by 90°.By adding the switchable liquid crystal layer, it is possible to switch between privacy protection mode and public mode, which is more noticeable when the optical film is integrated into the screen. The decrease in luminance density within the specified solid angle range described earlier is persistent for the optical film, but can be eliminated by the switchable liquid crystal layer. The first switching state corresponds to privacy protection mode, where the light maintains linear polarization. The second switching state corresponds to public mode, where the light is generally elliptically polarized, but other polarization methods can be adopted depending on the liquid crystal layer selected.In public mode, the luminance density in the specified solid angle range does not decrease or decreases only slightly, so that if this arrangement is applied to the screen, the image content can be perceived regardless of the observer's position (i.e., without restriction) within a range of technical feasibility. In privacy protection mode, the image content cannot be perceived by a person standing sideways (relative to the direction of the...). Petition 870250080945, dated 09 / 09 / 2025, page 83 / 132 15 / 43 first absorption axis). Alternatively, the liquid crystal layer can be arranged between the first polarization layer and the compensation layer closest to the liquid crystal layer.

[0034] This switchable liquid crystal layer is generally applied with a first static polarization layer to manufacture the switchable optical film. If the function of the switchable liquid crystal layer can be performed by the first switchable polarization layer, the switchable liquid crystal layer can be dispensed with. In this case, the first polarization layer can be constructed, for example, as a liquid crystal layer embedded with a dye, i.e., the so-called “Dye-LC-Zellen” (LC dye unit). This liquid crystal layer is especially suitable when the first absorption axis, i.e., the absorption axis of the first polarization layer, is parallel to the normal of the optical film surface.

[0035] Preferably, the restriction of vision within the specified solid angle range is achieved by minimizing the luminance density within the solid angle range: the components of the optical film are coordinated with each other so that, within the specified solid angle range ®, a loss function: is minimum, where T(φ, θ) is an angle-dependent transmittance and Ω is a solid angle. That is, a natural logarithm of an angle-resolved transmittance is calculated and integrated within the range of solid angles where privacy protection needs to be optimized. This logarithm is weighted so that different orders of magnitude of transmittance are taken into account in the optimization. Other weighting methods, such as linear weighting, can be adopted. The need to apply logarithms to Petition 870250080945, dated 09 / 09 / 2025, page 84 / 132 16 / 43 transmittance is eliminated. Commercially available optical design programs can be adopted to coordinate components with each other and perform the optical design of this disclosure in such a way that this condition is met, such as LCD MASTER® from Uniglobe Kisco or Tecwiz LCD 3D® from INCROPS.

[0036] In common uses, the limiting azimuth φιim is 30° to 40° to the left and to the right relative to the preferred direction, and / or the limiting polar angle θιim is 40° to 50° to the left and to the direction of the surface normal or the first absorption axis (if inclined relative to the surface normal).

[0037] If the film is not equipped with a switchable liquid crystal layer, the backlighting with the optical film can be integrated into the screen lighting device, and the backlighting can be integrated into the screen when the film is equipped with a switchable liquid crystal layer.

[0038] Specifically, the backlight with the optical film equipped with a non-switchable liquid crystal layer, i.e., without the switchable liquid crystal layer, can be inserted and then applied to the illumination device of a transmissive screen (especially an LCD display) in which the illumination device is configured to operate in two operating modes, (B1) (for free viewing mode) and (B2) (for restricted viewing mode). In restricted viewing mode, the light is emitted in a relatively restricted range of solid angles than in free viewing mode. The illumination device includes a backlight that extends in a flat manner and emits light. The backlight includes a backlight source and the aforementioned non-switchable optical film. If the second polarizing layer of the optical film is arranged in front Petition 870250080945, dated 09 / 09 / 2025, p. 85 / 132 17 / 43 of the first polarizer in the viewing direction, for the entire backlight (as is the case with the other technical solutions described below), the backlight source emits unpolarized light; and when the opposite arrangement is adopted, the light emitted by the backlight source can be (partially) polarized. For the observer viewing the lighting device, a plate-shaped light guide is arranged in front of the backlight in the viewing direction, with two large surfaces and a narrow side connecting them, and with an output coupling element on at least one of these large surfaces and / or within its volume. A luminous element is arranged laterally on at least one narrow side of the light guide. A linear polarizing filter is arranged in front of the backlight or in front of the light guide along the viewing direction.Optionally, the polarizing filter can correspond to the second polarizing layer of the optical film or adopt a special solution. Thus, the direction in which the light originates from the backlight and enters the linear polarizing filter is restricted. In operating mode (B2) for restricted viewing mode, the backlight is switched on and the luminous element is switched off. Only the backlight emits light in the restricted viewing angle range. In operating mode (B1) for free or public viewing mode, at least the luminous element is switched on, making it possible to compensate or overcompensate for the restricted illumination, which is achieved only by the backlight. Similarly, the backlight can be switched on or off in public viewing mode. In this case, the transmissive screen is positioned in front of the lighting device.

[0039] This disclosure also includes a screen that can be operated in at least two operating modes, (B1) (for free viewing mode) and (B2) (for restricted viewing mode). In the mode of Petition 870250080945, dated 09 / 09 / 2025, p. 86 / 132 18 / 43 Restricted viewing: Light is emitted to the observer within a relatively restricted viewing angle range or a range of solid angles compared to free viewing mode. In a technical solution with a switchable liquid crystal layer that can be alternated between two states, such a screen first includes a backlight that extends flat and emits light, and the aforementioned optical film. Optionally, the backlight can emit light directly; for example, it can be implemented as so-called "direct matrix backlighting." A linear polarization filter is placed in front of the backlight along the viewing direction. Optionally, the polarization filter can correspond to the second polarization layer of the optical film. Thus, the direction in which the light originates from the backlight and enters the linear polarization filter is restricted.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 be arranged in the transmission image reproduction device. The polarizing filter may be provided separately, where the polarizing filter is as close as possible to the image reproduction device in a stack of optical components. A typical image reproduction device includes a linear polarizer located above the LC layer and a linear polarizer located below the LC layer along the viewing direction, whereas the previous description involved a linear polarizer located below in the viewing direction. An above-located linear polarizer is essential for privacy protection applications.As mentioned earlier, the liquid crystal layer that can be switched between at least two states is in the first switching state in operating mode (B2) and in the second switching state in operating mode (B2).

[0040] Finally, this disclosure also includes another screen that Petition 870250080945, dated 09 / 09 / 2025, page 87 / 132 19 / 43 can be operated in at least two operating modes, (B1) (for free viewing mode) and (B2) (for restricted viewing mode). In restricted viewing mode, light is emitted to the observer in a relatively restricted viewing angle range or in a range of solid angles compared to free viewing mode. Such a screen includes OLED, microLED, or LCD image reproduction devices and an optical film arranged in front of the image reproduction device in the viewing direction. The optical film includes a liquid crystal layer that can be switched between at least two states. According to the previous definition of the first switching state and the second switching state, the liquid crystal layer is in the first switching state in operating mode (B2) and in the second switching state in operating mode (B2).

[0041] It is clear that, within the scope of this disclosure, the resources described above and below can be combined not only in the manner presented in this disclosure, but also in combination or separately in other ways. Brief Description of the Drawings

[0042] The present disclosure will be described in detail in combination with embodiments, with reference to drawings revealing substantive features of the present disclosure. Embodiments are for illustrative purposes only and do not constitute a limitation. For example, the description of an embodiment containing several elements or sets does not mean that all such elements or sets are indispensable. To be more precise, other embodiments may also include substitute elements and sets, reduced elements or sets, or additional elements or sets. Unless otherwise specified, elements or components of different embodiments may be combined with each other. A variant and modification described for a Petition 870250080945, dated 09 / 09 / 2025, page 88 / 132 20 / 43 of the embodiments can also be applied to other embodiments. The same element or corresponding element in different drawings is indicated by the same reference symbol and will not be repeated to avoid duplication. In the drawings: Figure 1A shows an optical film layer structure for controlling and restricting the observer's viewing angle range. Figure 1B shows an optical film layer structure for controlling and restricting the observer's viewing angle range. Figure 1C shows an optical film layer structure for controlling and restricting the observer's viewing angle range. Figure 2 shows a restriction of a viewing angle range. Figure 3 is an example of how this disclosure improves privacy protection. Figure 4A shows a privacy protection effect of an early technical solution using an optical film. Figure 4B shows a privacy protection effect of an early technical solution using an optical film. Figure 5A shows a privacy protection effect of a second technical solution for an optical film. Figure 5B shows a privacy protection effect of a second technical solution for an optical film. Figure 6A shows a privacy protection effect of a third technical solution for an optical film. Figure 6B shows a privacy protection effect of a third technical solution for an optical film. Figure 7A shows a polarization ellipse passing through an optical film. Figure 7B shows a polarization ellipse passing through a Petition 870250080945, dated 09 / 09 / 2025, page 89 / 132 21 / 43 optical film, Figure 7C shows a polarization ellipse passing through an optical film. Figure 7D shows a polarization ellipse passing through an optical film. Figure 7E shows a polarization ellipse passing through an optical film. Figure 7F shows a polarization ellipse passing through an optical film. Figure 7G shows a polarization ellipse passing through an optical film. Figure 8 shows a solution for a switchable optical film. Figure 9A shows an operational state of a lighting device with a non-switchable optical film. Figure 9B shows another operational state of a lighting device with a non-switchable optical film. Figure 10 shows a screen with a switchable optical film, and Figure 11 shows another screen with a switchable optical film. Detailed Description of the Invention

[0043] Figures 1A to 1C are various schematic optical film layer structures for controlling and restricting the observer's viewing angle range. The observer, not shown, is located above a top layer that has a surface with a normal parallel to the long side of a sheet in a leaf plane. The top layer seen from the observer's direction is a first polarization layer (1) in all three Figures 1A to 1C. The first polarization layer (1) has a first absorption axis oriented at an angle of 0° to 30° relative to the normal of the optical film surface. When the angle is 0°, the first polarization layer Petition 870250080945, dated 09 / 09 / 2025, pp. 90 / 132 22 / 43 (1) is a polarizer (Z) and, when the angle is different, the term “polarizer (Z*)” is used. The 0° angle is suitable, for example, for a laptop where the user is directly in front of the screen. The 30° angle is more advantageous, for example, in a motor vehicle, where a screen is placed between the driver's seat and the passenger's seat, and only the driver can see relevant information.

[0044] The lowest layer in Figures 1A to 1C is a second polarization layer (2) with a second absorption axis parallel to the surface of the optical film. That is, the second polarization layer (2) here is a linear polarizer.

[0045] At least one phase-shift compensation layer is disposed between the first polarization layer (1) and the second polarization layer (2) to improve the restriction of the viewing angle range. A single compensation layer or multiple compensation layers are provided according to the type of compensation layer. The compensation layer is, for example, a polymer film with uniaxial or biaxial birefringence. Such layers are advantageously connected to each other by means of a connection, for example, by optical bonding or by another material. For example, ultrasonic welding can be adopted. When extremely smooth surfaces are joined or pressed, they can be connected only by adhesion, with an anti-reflective layer as needed. A solution with one or more compensation layers can be adopted to improve the privacy protection effect, which will be described below.In an alternative not shown, the second polarization layer (2) can be arranged as the top layer in the direction of view, and the first polarization layer (1) is arranged behind it, where at least one phase shift compensation layer is always located between the first polarization layer (1) and the second polarization layer. Petition 870250080945, dated 09 / 09 / 2025, pp. 91 / 132 23 / 43 (2) .

[0046] In a first technical solution, also referred to as the first alternative or alternative i below, shown in Figure 1A, a first compensation layer (B*) (3) is arranged between the first polarization layer (1) and the second polarization layer (2). The first compensation layer (B*) (3) is a spatially homogeneous layer made of a biaxially birefringent material. Correspondingly, the material or the first compensation layer (B*) (3) has two optical axes and three principal refraction axes. The three principal refraction axes correspond to the refractive indices nx, ny, and nz, respectively, which is a common property of biaxially birefringent material. The symbols “x”, “y”, and “z” correspond to the axes of a Cartesian coordinate system.However, to achieve a privacy-protecting effect, the principal refraction axis corresponding to the minimum refractive index or the principal refraction axis corresponding to the maximum refractive index must be parallel to the first absorption axis.

[0047] The orientation of the first absorption axis determines the orientation of all other absorption axes or the orientation of the principal refraction axes of all types of compensation layers. If the first polarizing layer is, for example, a polarizer (Z), that is, its first absorption axis is parallel to the surface normal or perpendicular to the surface of the film, this means that the corresponding principal refraction axis, which corresponds to the minimum or maximum refractive index, is also parallel to the surface normal. Consequently, the other two principal refraction axes are in the plane where the surface of the optical film is located. In this case, the optical axis of the first compensation layer (B*) (3) of the compensation layer (B) is located in a plane perpendicular to the surface of the optical film. In this case, two solutions Petition 870250080945, dated 09 / 09 / 2025, page 92 / 132 24 / 43 construction can be adopted for the first compensation layer (B*) (3).

[0048] On the one hand, the first compensation layer (B*) (3) can be constructed as a compensation layer (-B). In this case, a polarizer (Z) is involved, so that in an imaginary Cartesian coordinate system (where the principal refraction axis and the optical axis of the compensation layer (B*) are defined), the z direction is associated with the direction perpendicular to the surface of the optical film. In this notation, the compensation layer (-B) satisfies a condition nx > ny > nz. Therefore, the minimum refractive index corresponding to the principal axis perpendicular to the surface of the optical film is denoted by nz. Furthermore, the principal refraction axis corresponding to the maximum refractive index nx is parallel to the second absorption axis of the second polarization layer (2).

[0049] On the other hand, the first compensation layer (B*) (3) can be constructed as a compensation layer (+B). Here, the z direction can be associated with the direction perpendicular to the surface of the optical film. In this notation, the compensation layer (+B) satisfies the condition nz > nx > ny. Therefore, the maximum refractive index corresponding to the principal axis perpendicular to the surface of the optical film is denoted by nz. 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).

[0050] In terms of all the technical solutions of the first alternative, the first compensation layer (B*) (3) satisfies a condition: hph. - ^-d |nx— ny| < 2π, where d represents the thickness of the first compensation layer, Δph represents the phase shift caused by the first Petition 870250080945, dated 09 / 09 / 2025, page 93 / 132 25 / 43 compensation layer (B*) and λ represents any wavelength specified in principle that satisfies this condition. Thus, an upper limit is defined for the phase delay of the first compensation layer (B*), and the maximum thickness is also specified indirectly.

[0051] In a second technical solution, whose basic structure is shown in Figure 1B and referred to as the second alternative or alternative ii below, at least two compensation layers made of uniaxial birefringent materials are arranged between the first polarization layer (1) and the second polarization layer (2). These are the first compensation layer (A*) (4) and the second compensation layer (A*) (5). The two compensation layers (A*) (4) and (5) are constructed to be spatially homogeneous in a previously defined manner. The first compensation layer (A*) (4) is made of a first uniaxial birefringent material with a first optical axis and two first principal refraction axes, wherein the first optical axis is perpendicular or parallel to the first absorption axis of the first polarization layer (1).The second compensation layer (A*) (5) is located behind the first compensation layer (A*) (4) when viewed from the observer's direction and is made of a second uniaxial birefringent material with a second optical axis and two second principal refraction axes. An orientation of the second optical axis of the second compensation layer (A*) (5) is specified according to the orientation of the first optical axis of the first compensation layer (A*) (4), in which the condition that the second optical axis is perpendicular to the first optical axis must be satisfied. Each of the two compensation layers (A*) (4) and (5) satisfies a condition:. = ^-d · |ne- no| < 2π Λ where d represents the thickness of a compensation layer. Petition 870250080945, dated 09 / 09 / 2025, page 94 / 132 26 / 43 respectively, ne represents an extraordinary refractive index and no represents the normal refractive index, Δph represents a phase change caused by the first compensation layer (A*) (4) or the second compensation layer (A*) (5), and λ represents any specified wavelength that satisfies this condition. These two compensation layers (A*) (4) and (5) can be made of the same material and / or have the same thickness, thus simplifying the manufacturing process.

[0052] Figure 1C shows an improvement in the second alternative. To more clearly define a range of solid angles, i.e., to obtain a greater reduction in internal luminance density compared to the luminance density outside the range of solid angles, and / or to obtain greater flexibility in the selection of components for the compensation layer, in the second alternative, a third compensation layer (C*) (6) is advantageously arranged between the first compensation layer (A*) and the second compensation layer (A*), which is also spatially homogeneous. The third compensation layer (C*) (6) is made of a third uniaxially birefringent material with a third optical axis and two third principal refraction axes, the third optical axis being 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 compensation layer (C*) (6).

[0053] In the case where the first polarization layer (1) is constructed as a polarizer (Z) and therefore the first absorption axis is perpendicular to the surface of the optical film, the first compensation layer (A*) (4) is constructed as a compensation layer (+A) and the second compensation layer (A*) (5) is constructed as a layer of Petition 870250080945, dated 09 / 09 / 2025, page 95 / 132 27 / 43 compensation (-A), or vice versa. When the third compensation layer (C*) (6) is provided, it is constructed as a compensation layer (-C) or a compensation layer (+C).

[0054] In the first and second alternatives, the material and thickness d of the compensation layer are specified in such a way that in a spherical coordinate system with its coordinate origin located on the film surface and in a film plane, the luminance density is minimal only within a specified range of solid angles (R). The range of solid angles (R) includes only a part of a possible perceptible half-space, that is, on the one hand, it includes an azimuth φ located on the film surface. When measured in a preferred direction in the plane where the film surface is located, |φ| or |180°-φ| is less than an absolute value of a specified limit azimuth φιim. In principle, the preferred direction can be selected arbitrarily, but it must be selected according to the applied optical film.When applying optical film to, for example, a screen with a fixed orientation (e.g., in a vehicle), the preferred orientation is selected so that it is parallel to an imaginary line between the eyes of an upright driver, i.e., it generally extends horizontally. The limiting azimuth φιim is specified according to a hypothetical use of the film. For example, for a notebook that needs to be protected from being viewed from the side on a train or other means of transport, a common value of the limiting azimuth φιim is 30° to 40° to the left and right of the preferred direction, where the preferred direction is generally parallel to the longer side of the screen, and the first absorption axis is parallel to the normal of the screen, so that a decrease in luminance density on all sides is symmetrical.

[0055] On the other hand, the range of solid angles with minimum luminance density also includes a polar angle θ. When measured relative to the first absorption axis and in a plane formed by the normal of Petition 870250080945, dated 09 / 09 / 2025, page 96 / 132 28 / 43 surface and the first absorption axis, or measured only with respect to the surface normal in a case where the first absorption axis is parallel to the surface normal, an absolute value of the polar angle is greater than a specified limiting polar angle θιim. Preferably, the specified limiting polar angle θιim is 40° to 50°, which is determined depending on the application. When applied to the screen illustrated above, the optical film effectively restricts vision, as the luminance density is minimal within the range of solid angles described above. Therefore, in an ideal situation, an observer in a position within the aforementioned range of solid angles relative to the spherical coordinate system of the optical film will not perceive anything on the screen or, at least, will not be able to identify the content due to the minimal luminance density within the range.

[0056] Preferably, the restriction of vision within the specified solid angle range is achieved by minimizing the luminance density within the solid angle range: the components of the optical film are coordinated with each other so that, within the specified solid angle range (R), the loss function is minimal, where Τ(φ, θ) is an angle-dependent transmittance and Ω is a solid angle. That is, a natural logarithm of an angle-resolved transmittance is calculated and integrated within the solid angle range where privacy protection needs to be optimized. Thus, not only a horizontal viewing angle is included, but also a viewing angle of a vertical gaze that deviates from a real observer by 0° (along the surface normal), i.e., a viewing angle in an upward or downward direction, is included. For example, a third observer standing next to a device user seated in privacy mode is also included.Finally, a significant improvement in privacy protection in the viewing angle compared to the state of the art is achieved. Logarithms are used for weighting at different orders. Petition 870250080945, dated 09 / 09 / 2025, page 97 / 132 29 / 43 magnitude. Other weighting methods, such as linear weighting, may be adopted.

[0057] This is illustrated in combination with Figures 2 and 3. Figure 2 shows a projection of the specified solid angle range (R) onto the optical film plane as a black area, also known as a cone image. Privacy protection needs to be enhanced in this range so that the luminance density is as low as possible. In this example, the solid angle range (R) is specified so that the limiting azimuth φ^ is 40° - thus forming the black area above and below a horizontal axis, and the limiting polar angle θιim is also 40° - corresponding to a recessed area on the right and left sides of a midpoint. In this case, an inner concentric circle corresponds to the polar angle θ of 40°. For this specified solid angle range, the loss function, i.e., an integration of the logarithmic transmittance, is minimized.The commercially available optical design procedures mentioned earlier can be used to coordinate components in order to satisfy this condition.

[0058] Finally, even for a vertical viewing angle other than 0° (corresponding to looking vertically at the surface of the optical film), an enhanced privacy effect can be obtained in a side orientation. Referring to the vertical viewing angle of 30° in Figure 3 and the optical film in the second alternative, the compensation layer (+A) and the compensation layer (-A) are included, on the one hand, and the compensation layer (-C), on the other. The first polarization layer (1) is constructed as the polarizer (Z), so that the first absorption axis is parallel to the normal of the surface of the optical film. The figure shows the privacy protection effect with any unit, i.e., according to a horizontal viewing angle with the unit in degrees, the luminance density is normalized to an angle of 0°, from which one can see how bright it is inside. Petition 870250080945, dated 09 / 09 / 2025, pp. 98 / 132 30 / 43 an angle range for screen privacy protection compared to an angle range for no privacy protection. For example, selecting the preferred direction parallel to a horizontal direction is related to the observer's frame of reference. That is, the horizontal direction corresponds to an imaginary line connecting the observer's eyes, and the vertical direction is perpendicular to it. A solid line corresponds to a privacy effect obtained in the prior art with only the polarizer (Z) and no spatially homogeneous compensation layer at a vertical viewing angle of 30°. A chain line corresponds to a privacy protection effect from the combination of two types (-A) and (+A) of compensation layers (A*). A dashed line corresponds to a privacy protection effect from the addition of a compensation layer (-C).The compensation layer (A*) is not fully optimized in this example; therefore, in this example, the combination with the compensation layer (-C) is not enhanced. However, under normal circumstances, privacy protection at an angle of approximately 30° can be enhanced by the compensation layer (C*). Privacy protection in the side orientation at an angle of up to approximately 60° is significantly enhanced. Privacy protection at a large angle, greater than 60°, is slightly enhanced, but still represents an improvement over the prior art. This privacy protection is amplified by the logarithmic scale, but is not obvious in practice. At a vertical viewing angle of 0° not shown here, the prior art optical film and the optical film described above and below with the additional compensation layer have substantially the same result, which corresponds approximately to the dashed line or chain line.

[0059] The range of solid angles (R) shown in Figure 2 is for illustrative purposes only and can be adjusted as needed to improve privacy protection at the vertical viewing angle, for example, at an angle Petition 870250080945, dated 09 / 09 / 2025, page 99 / 132 31 / 43 of a horizontal view of 0°, in the case of a laptop, corresponding to the observer standing directly behind the seated user. In this case, for example, when the black solid angle band in Figure 2 is set to 40°, it completely encircles the concentric circle.

[0060] Further examples are shown in Figures 4A and 4B, Figures 5A and 5B, and Figures 6A and 6B, where the range of solid angles (R) shown in Figure 2 is specified. Figures 4A, 5A, and 6A show the privacy protection effect for a vertical viewing angle of 0°, and Figures 4B, 5B, and 6B show the privacy protection effect for a vertical viewing angle of 30°. A curve with a solid line always corresponds to an optical film with only a first polarization layer (Z*) and no additional spatially homogeneous compensation layer.

[0061] Figure 4A and Figure 4B show the privacy effect of an optical film with the structure of the first alternative shown in Figure 1A, which includes the first compensation layer (B*) (3). The same optical function is achieved for the biaxially birefringent layer of multiple combinations of nx, ny and nz, therefore, such a layer is classified by two other parameters that take this into account, namely, by a parameter Re= («x -ny)-of a parameter; jy _ (nx-nz)Z{nx~ny)

[0062] The dashed curves are obtained in the intermediate green wavelength range of visible light, at a wavelength λ = 550 nm, where the human eye exhibits the greatest sensitivity, and at a thickness d = 5.25 μm, Re = 132 and Nz = 3.84. It can be inferred from nx that there must be a correlation between the refractive indices. For example, nx = 1.6246, ny = 1.6 and nz = 1.5287. To produce a correct layer with this calculated refractive index, a large number of manufacturing methods are known in Petition 870250080945, dated 09 / 09 / 2025, pages 100 / 132 32 / 43 state of the art to highly control the refractive index. If a material with a desired refractive index ratio is selected, the thickness d is adjusted to meet Nz. In addition to the above parameters, other combinations can be used to obtain significant improvements. Thus, the privacy effect characteristics shown by the dashed lines are produced, where Re = 75 and Nz = 3.84. The values ​​are only illustrative and can be included in each case with a tolerance of + / - 20% without significantly reducing the privacy effect.

[0063] Figures 5A and 5B show the privacy protection effect of the optical film with the structure of the second alternative shown in Figure 1C, which has the first compensation layer (A*) (4), the second compensation layer (A*) (5) and the third compensation layer (C*) (6) located between the two layers. The first absorption axis of the first polarization layer (1) is also perpendicular to the surface, so the first polarization layer (1) is the polarizer (Z). Correspondingly, the first compensation layer (A*) (4) is constructed as a compensation layer (+A) with positive birefringence, the second compensation layer (A*) (5) is constructed as a compensation layer (-A) with negative birefringence and the third compensation layer (C*) (6) is constructed as a compensation layer (-C) with negative birefringence.Alternatively, the first compensation layer (A*) (4) can be constructed as a compensation layer (-A) with negative birefringence, the second compensation layer (A*) (5) can be constructed as a compensation layer (+A) with positive birefringence, and the third compensation layer (C*) (6) can be constructed as a compensation layer (+C) with negative birefringence, where negative birefringence refers to a case of ne < no and positive birefringence refers to a case of ne > no. Petition 870250080945, dated 09 / 09 / 2025, pp. 101 / 132 33 / 43

[0064] At a vertical viewing angle of 0°, Figure 5A corresponds to a direct top view of the film along the surface normal; no improvement is achieved by the three additional compensation layers, except for the polarizer (Z); while at a vertical viewing angle of 30°, the enhanced privacy effect can be clearly seen in Figure 5B. The improvement shown in Figures 5A and 5B can be achieved by a series of compensation layers, for the first compensation layer (+A) with a condition d^(no-ne) = -264 nm to be satisfied and for the second compensation layer (-A) with a condition d^(ne-no) = -264 nm to be satisfied, each of which has a tolerance of 20%. For the third compensation layer (-C), a condition d^(ne-no) = -22 nm is satisfied, where the tolerance is greater than + / -10 nm. For the entire relatively thin compensation layer (C*), the tolerance is + / -10 nm or 20%, whichever is greater.In an alternative technical solution with the first offset layer (-A), the symbols are inverted accordingly.

[0065] Figures 6A and 6B show the privacy protection effect of the optical film with the structure of the second alternative shown in Figure 1C, which has the first compensation layer (A*) (4) and the second compensation layer (A*) (5), and the additional third compensation layer (C*) (6) located between the two layers. Unlike Figures 5A and 5B, the first absorption axis of the first polarization layer here is inclined at 20° towards the surface relative to the surface normal, so that the first polarization layer is the polarizer (Z*). This orientation also specifies how the optical axes of the offset layer (A*) and the offset layer (C*) should be arranged to achieve the privacy protection effect. To fabricate the inclined offset layer, for example, optical orientation and polymerization of liquid crystals (LC) can be used. Without restrictions Petition 870250080945, dated 09 / 09 / 2025, pages 102 / 132 34 / 43 overall, the first compensation layer (A*) (4) is constructed as the compensation layer (-A*), the second compensation layer (A*) (5) is constructed as the compensation layer (+A*) and, correspondingly, the third compensation layer (C*) (6) is constructed as the compensation layer (-C*). The improvements shown in Figures 6A and 6B can be achieved by a series of compensation layers, for the first compensation layer (+A*) with a condition d^(ne-no) = 264 nm to be satisfied and for the second compensation layer (-A*) with a condition d*(no-ne) = -264 nm to be satisfied, each of which has a tolerance of 20%. For the third compensation layer (-C*), a condition d*(ne-no) = -82 nm is satisfied, where the tolerance is also 20%. In an alternative technical solution with the first layer of compensation (-A*), the symbols are inverted accordingly.

[0066] In Figures 7A to 7F, a function of each layer is described in detail by means of a polarization ellipse, taking as an example the optical film in the second alternative shown in Figure 1C, where the first absorption axis of the first polarization layer (1) is parallel to the normal of the optical film surface. For comparison, Figure 7G shows an optical polarization by the layer structure without the additional compensation layer of the prior art. Assume that the observer's gaze follows the normal of the optical film surface. Each of Figures 7A to 7G shows multiple polarization ellipses distributed in a circle around the origin of the coordinate system. The position of each polarization ellipse corresponds to a respective viewing angle towards the optical film surface. The viewing angle at the origin of the coordinate system corresponds to the surface normal, i.e., perpendicular to the top view of the optical film surface.Without general restrictions, a direction along a longitudinal side of a sheet plane and parallel to a short side of the sheet plane is called a direction. Petition 870250080945, dated 09 / 09 / 2025, pp. 103 / 132 35 / 43 x, and a direction perpendicular to it is called the y-direction. The x-direction also corresponds to the preferred direction and is parallel to the imaginary line connecting the observer's eyes, also being called the horizontal direction to follow. That is, there are several polarization ellipses on the x-axis of the coordinate system in Figures 7A to 7G, which correspond to the angle of view deviating horizontally by only zero, and to the observer moving laterally away from the origin. There are several polarization ellipses on the y-axis, and the angle of view deviating vertically by only zero, corresponding to the observer moving vertically up and down from the origin position.The "vertical" movement or displacement here does not mean that the observer moves away from the optical film along the surface normal; that is, it does not mean that the observer moves along the surface normal in the horizontal plane formed between the surface normal and the horizontal direction between the observer's eyes. Instead, it refers to displacement perpendicular to the plane. For example, in the case where a first observer, seated, looks directly at the optical film along the surface normal, the viewing angle of the second observer, standing directly behind the first observer, is only shifted vertically and located on the y-axis. To facilitate understanding, two concentric circles are shown in Figures 7A to 7G. An inner circle limits a viewing angle cone of up to 25° in each direction, and an outer circle limits a viewing angle cone of up to 45° in each direction.The outermost viewing angle is 90°, which is imperceptible in reality.

[0067] Figure 7A shows circularly polarized light emitted by a backlight onto the optical film. This light first enters the second polarization layer (2) with the second absorption axis and is linearly polarized, since the second absorption axis of the second polarization layer (2) is oriented parallel to the surface of the film, in this Petition 870250080945, dated 09 / 09 / 2025, pp. 104 / 132 36 / 43 case along the horizontal direction or, in general, along the imaginary line connecting the observer's eyes. The horizontal direction also corresponds to the preferred direction.

[0068] After passing through the second polarization layer, linearly polarized light enters the second compensation layer (A*) (5), which is constructed as the compensation layer (-A). The polarization remains almost constant, especially horizontally and vertically, but within a different viewing angle range, s-polarized light can be obtained over a large area – in the top view – after passing through the second polarization layer, as seen in Figure 7C, i.e., light with a relevant electric field vector perpendicular to a plane of incidence (the plane formed by the surface normal and a direction of incidence). Figure 7D shows an angular resolution polarization after the light passes through the next layer, i.e., the third compensation layer (C*) (6). This compensation layer is constructed here as the compensation layer (+C). However, a change is difficult to see in the graph due to the lack of birefringence and its construction as the compensation layer (C*).Figure 7E shows a polarization of light after passing through the first compensation layer (A*) (4), which is constructed as the compensation layer (+A). Most of the light is approximately polarized in p, i.e., the electric field vector is parallel to the plane of incidence, so that the absorption of light in a non-vertical propagation direction increases due to the first subsequent polarization layer, i.e., the polarization layer (Z). This aspect is achieved by the interaction of the three compensation layers. The privacy protection effect is greatly enhanced.

[0069] Finally, Figure 7F shows the polarization of light after passing through the first polarization layer (1), i.e., the polarizer (Z). For comparison, the polarization of light in the state of the art is shown in Figure Petition 870250080945, dated 09 / 09 / 2025, pages 105 / 132 37 / 43 7G, where one polarization layer (Z) is directly connected to the second polarization layer. The closer the polarized ellipse is to a point, the lower the luminance density. It is clear here that the luminance density in the black area in Figure 2 is much lower than that of the prior art, therefore the privacy protection effect is enhanced. This is achieved by: as in the prior art, the luminance density is not minimized throughout the half-space – except for the narrow viewing cone – but only in a real part of the half-space other than the viewing cone, i.e., the range of solid angles (R) is specified. Specifically, a loss function G = / RlnT(0,^ díl is minimized within the specified range of solid angles (R), where T(φ, θ) is an angle-dependent transmittance and Ω is a solid angle. Thus, the luminance density within the desired range is significantly reduced, resulting in greater privacy protection.

[0070] Figure 8 shows a technical solution of an optical film with the first compensation layer (A*) (4) and the second compensation layer (A*) (5), similar to those in Figure 1B, but an additional liquid crystal layer (7) is arranged between the second polarization layer (2) and the second compensation layer (A*) (5), which can be switched between at least two states. The liquid crystal layer (7) is constructed so as to transmit the light transmitted by the second polarization layer (2) with an unchanged polarization or a polarization rotated by 90° in a first switching state, and to transmit the light transmitted by the second polarization layer (2) in a circular or elliptical polarization in a second switching state. Obviously, the liquid crystal layer (7) with the switching method can be applied to other technical solutions of optical films, especially the technical solutions shown in Figures 1A and 1C. Petition 870250080945, dated 09 / 09 / 2025, pp. 106 / 132 38 / 43

[0071] Thus, for example, a screen is obtained as shown in Figures 10 and 11. Figure 10 shows a screen that can be operated in at least two operating modes, (B1) (for free display mode) and (B2) (for restricted display mode). In restricted display mode, light is emitted in a relatively restricted viewing angle range for the observer compared to free display mode. To switch between the two operating modes, the screen includes a backlight (8), which extends in a flat shape, an optical film (not specifically shown here) with the liquid crystal layer (7), which can be switched between at least two states, and emits light, which is represented here by multiple light sources (9).This is merely a schematic illustration, for example, a light guide with a surface emitter or with edge and surface structured illumination, which may optionally include an optical layer, such as a diffusion film or a prismatic grid film. Optionally, the backlight may emit light directly, for example, being constructed as a “Direct Matrix Backlight Dimming”. A linear polarizing filter (10) is disposed in front of the backlight (8) along the viewing direction, which restricts the propagation direction of the light emitted by the backlight (8) and which penetrates the linear polarizing filter (10). A transmissive image reproduction device (11) is disposed in front of the backlight (8) along the viewing direction. The linear polarizing filter (10) is disposed behind the transmissive image reproduction device (11) along the viewing direction.The polarization filter should be as close as possible to the image reproduction device, i.e., with the fewest possible layers between them. Preferably, the linear polarization filter (10) is disposed in the transmissive image reproduction device (11), i.e., as part of or integrated into it. In operating mode (B2), the liquid crystal layer (7), which can be switched between at least two states, is. Petition 870250080945, dated 09 / 09 / 2025, pp. 107 / 132 39 / 43 in the first switching state, and in operating mode (B1), the liquid crystal layer (7), which can be switched between at least two states, is in the second switching state. In other words, by the switchable liquid crystal layer, a switching is performed between public operating mode and privacy mode, in public operating mode, the image content displayed on the screen can be viewed from various viewing angles without restriction, and in privacy mode, the displayed image content is only visible with sufficient brightness within a narrow viewing angle range of a cone around the first absorption axis of the first polarization layer (1).

[0072] Figure 11 shows another technical solution for a screen that can be operated in at least two operating modes, (B1) (for free display mode) and (B2) (for restricted display mode). In the restricted display mode, light is emitted to the observer in a viewing angle range relatively restricted to that of the free display mode. The screen includes an image reproduction device (12) with a structure disclosed in the prior art and can be constructed, for example, as an active luminous image reproduction device (12) based on OLED or microLED, or as a passive (i.e., illuminated) luminous image reproduction device based on LCD (12). An optical film is disposed in front of the image reproduction device (12) along the viewing direction and includes the liquid crystal layer (7) which can be switched between at least two states.The optical film is constructed here, for example, according to the first alternative, in which the first compensation layer (B*) (3), spatially homogeneous and made of a biaxial birefringent material, is disposed between the first polarization layer (1) and the second polarization layer (2). The second polarization layer (2) can be constructed as a rear polarizer for an LC screen of the image reproduction device (12). Naturally, all other technical solutions of the optical film with a. Petition 870250080945, dated 09 / 09 / 2025, pages 108 / 132 40 / 43 switchable liquid crystal layer (7) can be adopted. Similar to the screen mentioned previously, the liquid crystal layer (7), which can be switched between at least two states, is also in the first switching state in operating mode (B2) and in the second switching state in operating mode (B1). The technical solution is particularly suitable for adapting existing screens.

[0073] Alternatively, an optical film without the switchable liquid crystal layer (7) can be adopted to produce a lighting device for a 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 the restricted viewing mode, the light is emitted in a relatively restricted range of solid angles compared to the free viewing mode. Examples of the lighting device in these two operating modes are shown in Figures 9A and 9B. If the lighting device is combined with the image reproduction device that displays the image content upstream of the viewing direction, a screen is obtained that can be switched between the two operating modes (B1) and (B2).

[0074] The lighting device shown in Figures 9A and 9B includes a flat, extending backlight (13) integrated into a static, i.e., non-switchable optical film, as illustrated in Figures 1A to 1C. A plate-shaped light guide (14) is arranged in front of the backlight (13) in the viewing direction, which includes an output coupling element on at least one of its large surfaces and / or within its volume. In the example shown, the output coupling element (15) is arranged in the volume of the light guide (14). A linear polarization filter (16) is arranged in front of the backlight (13) or in front of the light guide (14) along the viewing direction. Thus, in principle, the direction of propagation of the light emitted by the backlight (13), penetrating the optical film and then Petition 870250080945, dated 09 / 09 / 2025, pages 109 / 132 41 / 43 in the linear polarization filter (16), is limited. Optionally, the linear polarization filter (16) can function as a second polarization layer (2), i.e., it can be equivalent to the second polarization layer (2). On at least one narrow side of the light guide (14) – in this case, on two narrow sides – are laterally arranged luminous elements (17), which emit light to the light guide (14) when switched on. The light incident by the luminous elements (17) is reflected back and forth in the light guide (14) by total reflection until it strikes the output coupling element (15), which deflects the light so that it shines out through the surface of the light guide (14) towards the observer. The output coupling element (15) is configured to deflect the light almost entirely in that direction and allow the light from the backlight (13) to pass almost unimpeded.

[0075] Figure 9A shows the lighting device in operating mode (B2) for restricted viewing mode, in which only a smaller, usually conical, range of solid angles is illuminated, indicated by an arrow on the surface of the light guide (14). In this case, only the backlight (13) is switched on and the luminous elements (17) must be switched off. Figure 9B shows the lighting device in operating mode (B1) for public viewing mode, in which light is emitted over a much larger or wider range of solid angles than in operating mode (B2), also represented by an arrow on the light guide (14). In this case, the luminous elements (17) must be switched on, and the light emitted in the light guide (14) and emitted and coupled by the output coupling element (15) is configured to widen the range of solid angles to be illuminated. The backlight (13) can be switched on or off in operating mode (B1).When the backlight (13) is switched off, homogeneous illumination across the entire range of solid angles is generally obtained in operating mode (B1).

[0076] By means of the passive image reproduction device Petition 870250080945, dated 09 / 09 / 2025, pages 110 / 132 42 / 43 illuminated from behind by the lighting device shown in Figure 9A and Figure 9B, the restricted viewing mode (B2) or the public viewing mode (B1) is generated for the observer looking at the image content displayed on the image playback device, depending on whether the luminous elements (17) are on or off.

[0077] The above optical film can be widely used in any situation where it is necessary to display and / or enter confidential information, such as PIN entry, display of data on ATMs or payment terminals, password entry or reading emails on mobile devices, by means of the image reproduction device and a dedicated lighting device, as needed. This disclosure can be applied, in particular, to a motor vehicle in order to selectively block interfering image content for a driver or passenger. [Description of reference signs] 1: First polarization layer; 2: Second polarization layer; 3: First compensation layer (B*); 4: First compensation layer (A*); 5: Second compensation layer (A*); 6: Third compensation layer (C*); 7: Liquid crystal layer; 8: Backlighting; 9: Light source; 10: Linear polarization filter; 11: Image reproduction device; 12: Image reproduction device; 13: Backlighting; 14: Light guide; Petition 870250080945, dated 09 / 09 / 2025, pages 111 / 132 43 / 43 15: Output coupling element; 16: Linear polarization filter; 17: Luminous element; A: Range of solid angles. Petition 870250080945, dated 09 / 09 / 2025, pages 112 / 132

Claims

1 / 12 Claims 1. BACKLIGHTING (13), characterized by extending in a planar manner, emitting light and comprising an optical film to control and restrict the viewing angle range of an observer, the optical film comprising: a first polarization layer (1) with a first absorption axis that is oriented at an angle of 0° to 30° from a surface normal of the optical film, at least one phase shift compensation layer to improve a restriction of the viewing angle range, a second polarization layer (2) with a second absorption axis that is oriented parallel to a surface of the optical film, wherein, between the first polarization layer (1) and the second polarization layer (2), i.e. in a first alternative, a first compensation layer (B*) (3) is disposed,which is formed to be spatially homogeneous and made of a first biaxially birefringent material having two optical axes and three principal refractive axes, wherein the principal refractive axes are in one-to-one correspondence with the refractive indices nx, ny, nz, wherein the principal refractive axis to which a minimum refractive index corresponds or the principal refractive axis to which a maximum refractive index corresponds is parallel to the first absorption axis, and wherein for the first compensation layer (B*) (3), a thickness d of the first compensation layer (B*) (3), a phase shift Δph and a specified wavelength λ satisfy a condition 2π . . àph — — d · 1¾ — n^l < 2π , Λ ii. in a second alternative, at least two layers of Petition 870250080945, of 09 / 09 / 2025, page. 113 / 132 2 / 12 compensation made of uniaxially birefringent materials are arranged,wherein a first compensation layer “A*” (4) which is formed to be spatially homogeneous, is made of a first uniaxially birefringent material having a first optical axis and two first principal refractive axes which are different from each other, with the first optical axis being perpendicular or parallel to the first absorption axis of the first polarization layer (1), and when viewed in the direction of the observer at the rear of the same, a second compensation layer “A*” (5) which is formed to be spatially homogeneous is disposed, which is made of a second uniaxially birefringent material having a second optical axis and two second principal refractive axes, with the second optical axis being perpendicular to the first optical axis, wherein, for each of the compensation layers, a thickness d of each of the compensation layers, an extraordinary refractive index ne and an ordinary refractive index no,A phase shift Δph and a specified wavelength λ satisfy a condition: 2π ^ph = —d |ne -n0| < 2tt , Z wherein, in both alternatives ie ii, the materials and thicknesses d of the compensation layers are specified such that, measured in a spherical coordinate system with its origin on a film surface and in a plane of the film surface, a luminance density is minimum only in a specified range of solid angles (R) comprising: an azimuth φ with |φ| and |180° -φ| being less than an absolute value of a specified limit azimuth φιim, measured relative to a preferred direction in the plane of the film surface, and Petition 870250080945, dated 09 / 09 / 2025, p. 114 / 132 3 / 12 a polar angle θ, whose absolute value is greater than a specified limiting polar angle θlim, measured with respect to the surface normal, or, measured with respect to the first absorption axis and in a plane defined by the surface normal and the first absorption axis,if the first absorption axis is not parallel to the normal of the surface.

2. BACKLIGHTING (13), according to claim 1 and alternative ii, characterized by a third compensation layer “C*” (6) that is formed to be spatially homogeneous, being disposed between the first compensation layer “A*” and the second compensation layer “A*”, and being made of a third uniaxially birefringent material having a third optical axis and two third principal refractive axes, with the third optical axis being parallel to the first absorption axis of the first polarization layer (1).

3. BACKLIGHTING (13), according to any one of claims 1 to 2, characterized in that the first absorption axis is oriented perpendicular to the surface of the film.

4. BACKLIGHTING (13), according to claim 3 and alternative i, characterized in that the principal refractive axis to which the minimum refractive index corresponds is parallel to the first absorption axis, wherein the first “B*” compensation layer (3) is constructed as a “-B” compensation layer, where nx > ny > nz, with the principal refractive axis to which the minimum refractive index nz corresponds being parallel to the surface normal and with the principal refractive axis to which the maximum refractive index nx corresponds being parallel to the second absorption axis of the second polarization layer (2).

5. BACKLIGHTING (13), according to claim 3 and alternative i, characterized in that the principal refraction axis corresponding to the maximum refractive index is parallel to the first absorption axis, wherein the first compensation layer “B*” (3) is constructed as a compensation layer “+B”, where nz > nx > ny, with the principal refraction axis corresponding to the maximum refractive index nz being parallel to the surface normal and with the principal refraction axis corresponding to the minimum refractive index ny being parallel to the second absorption axis of the second polarization layer (2).

6. BACKLIGHTING (13), according to claim 3 and alternative ii, characterized in that the first compensation layer “A*” (4) is constructed as a compensation layer “+A”, the second compensation layer “A*” (5) is constructed as a compensation layer “-A”, or vice versa, and in the case of a third compensation layer “C*” (6) being provided, the third compensation layer “C*” is constructed as a compensation layer “-C” or “+C”.

7. BACKLIGHTING (13), according to claim 1 and alternative ii, characterized in that both the first “A*” compensation layer (4) and the second “A*” compensation layer (5) have the same structure.

8. BACKLIGHTING (13), according to any one of claims 1 to 2, characterized by a liquid crystal layer (7) that can be switched between at least two states being disposed between the second polarization layer (2) and a compensation layer disposed closer to the second polarization layer, and being constructed to transmit light transmitted by the second polarization layer (2) with unchanged polarization or polarization rotated by 90° in a first switching state and to transmit light with circular, elliptical or linear polarization in a second switching state.

9. BACKLIGHTING (13), according to any one of claims 1 to 2, characterized by a liquid crystal layer (7) that Petition 870250080945, dated 09 / 09 / 2025, p. 116 / 132 5 / 12 can be switched between at least two states, being disposed between the first polarization layer (1) and a compensation layer disposed closer to the first polarization layer, and being constructed to transmit light transmitted by the first polarization layer (1) with unaltered polarization or polarization rotated by 90° in a first switching state and to transmit light with circular, elliptical or linear polarization in a second switching state.

10. BACKLIGHTING (13), according to any one of claims 1 to 2, characterized in that a loss function 4 ln 7(0,0) díl is minimal in the specified solid angle range (R), wherein Τ(φ, Θ) is an angle-dependent transmission and Ω denotes the solid angle range.

11. BACKLIGHTING (13), according to any one of claims 1 to 2, characterized in that the limiting azimuth φιim is between 30° and 40° to the left and to the right of the preferred direction and / or the limiting polar angle θ«η is between 40° and 50°.

12. LIGHTING DEVICE FOR A SCREEN, characterized in that the lighting device is configured to be operable in at least two operating modes (B1) for a free viewing mode and (B2) for a restricted viewing mode in which light is emitted in a range of solid angles that is relatively restricted compared to the free viewing mode, and comprising: the backlighting (13), as defined in any of claims 1 to 7, 10 or 11, a plate-shaped light guide (14) located in front of the backlighting (13) in a viewing direction and comprising an output coupling element (15) on at least one of the large surfaces and / or within its volume, a luminous element (17) arranged laterally in at least Petition 870250080945, dated 09 / 09 / 2025, page.117 / 132 6 / 12 a narrow side of the light guide (14), and a linear polarization filter (16) disposed in front of the backlight (13) or in front of the light guide in the viewing direction, whereby the light originating from the backlight (13) and entering the linear polarization filter (16) is restricted in its direction of propagation, wherein the backlight (13) is switched on and the light element (17) is switched off in operating mode (B2), and wherein at least the light element (17) is switched on in operating mode (B1).

13. SCREEN, characterized by being operable in at least two operating modes (B1) for a free viewing mode and (B2) for a restricted viewing mode in which light is emitted to an observer in a viewing angle range that is relatively restricted compared to the free viewing mode, comprising: the backlight (8), as defined in any one of claims 8 to 9, comprising a liquid crystal layer (7) switchable between at least two states, a linear polarization filter (10) disposed in front of the backlight (8) in a viewing direction, whereby the light originating from the backlight (8) and entering the linear polarization filter (10) is restricted in its direction of propagation, and a transmissive image reproduction device (11) that is disposed in front of the backlight (8) in the viewing direction, and in which or behind which the linear polarization filter (10) is disposed,wherein in operating mode (B2) the liquid crystal layer (7) switchable between at least two states is in the first switching state, and wherein in operating mode (B1) the liquid crystal layer (7) switchable between at least two states is in the second switching state. Petition 870250080945, dated 09 / 09 / 2025, p. 118 / 132 7 / 12, 14. SCREEN, characterized by being operable in at least two operating modes (B1) for a free viewing mode and (B2) for a restricted viewing mode in which light is emitted in a viewing angle range that is relatively restricted compared to the free viewing mode, comprising: an image reproduction device (12), an optical film in front of the image reproduction device (12) in a viewing direction and comprising a liquid crystal layer (7) switchable between at least two states, wherein in operating mode (B2) the liquid crystal layer (7) is in a first switching state, and wherein in operating mode (B1) the liquid crystal layer (7) is in a second switching state, the optical film comprising a first polarization layer (1) having a first absorption axis that is oriented at an angle of 0° to 30° from a normal surface of the optical film,at least one phase-shift compensation layer to improve a restriction of the viewing angle range, and a second polarization layer (2) having a second absorption axis that is oriented parallel to a surface of the optical film, wherein between the first polarization layer (1) and the second polarization layer (2), i.e. in a first alternative, a first compensation layer (B*) (3) is disposed, which is spatially homogeneously formed and made of a first biaxially birefringent material having two optical axes and three principal refractive axes, wherein the principal refractive axes are in one-to-one correspondence with the refractive indices nx, ny, nz, wherein the principal refractive axis to which corresponds an index of Petition 870250080945, dated 09 / 09 / 2025, page. 119 / 132 8 / 12 minimum refraction or the principal refractive axis to which a maximum refractive index corresponds is parallel to the first absorption axis,and wherein for the first compensation layer (B*) (3), a thickness d of the first compensation layer (B*) (3), a phase shift Δph and a specified wavelength λ satisfy a condition: 2π . . àph — — d 1¾ — n^l < 2π , Λ ii. in a second alternative, at least two compensation layers made of uniaxially birefringent materials are arranged, wherein a first compensation layer “A*” (4) which is formed to be spatially homogeneous is made of a first uniaxially birefringent material having a first optical axis and two first refractive principal axes which are different from each other, with the first optical axis being perpendicular or parallel to the first absorption axis of the first polarization layer (1), and when viewed in the direction of the observer at the rear of the same, a second compensation layer “A*” (5) which is formed to be spatially homogeneous is arranged,which is made of a second uniaxially birefringent material having a second optical axis and two second principal refractive axes, with the second optical axis being perpendicular to the first optical axis, wherein for each of the compensation layers, a thickness d of each of the compensation layers, an extraordinary refractive index ne and an ordinary refractive index no, a phase shift Δph and a specified wavelength λ satisfy a condition: 2π àph = —d |ne -n0| < 2tt, wherein, in both alternatives ie ii, the materials and thicknesses d of the compensation layers are specified so that, measured in Petition 870250080945, dated 09 / 09 / 2025, p. 120 / 132 9 / 12 a spherical coordinate system with its origin on a surface of the film and on a plane of the surface of the film,a luminance density is minimum only in a specified range of solid angles (R) comprising: an azimuth φ with |φ| and |180° -φ| being less than an absolute value of a specified limiting azimuth φιim, measured relative to a preferred direction in the plane of the film surface, and a polar angle θ, whose absolute value is greater than a specified limiting polar angle θlim, measured relative to the surface normal, or, measured relative to the first absorption axis and in a plane defined by the surface normal and the first absorption axis, if the first absorption axis is not parallel to the surface normal, wherein a liquid crystal layer (7) switchable between at least two states is disposed between the second polarization layer (2) and a compensation layer disposed closer to the second polarization layer,and is constructed to transmit light transmitted by the second polarization layer (2) with unchanged polarization or polarization rotated by 90° in a first switching state and to transmit light with circular, elliptical or linear polarization in a second switching state, or in which a liquid crystal layer (7) switchable between at least two states is disposed between the first polarization layer (1) and a compensation layer disposed closer to the first polarization layer, and is constructed to transmit light transmitted by the first polarization layer (1) with unchanged polarization or polarization rotated by 90° in a first switching state and to transmit light with circular, elliptical or linear polarization in a second switching state.

15. SCREEN, according to claim 14 and alternative ii, Petition 870250080945, dated 09 / 09 / 2025, pp. 121 / 132 10 / 12 characterized by a third compensation layer “C*” (6), which is formed to be spatially homogeneous, is disposed between the first compensation layer “A*” and the second compensation layer “A*”, and is made of a third uniaxially birefringent material having a third optical axis and two third principal refractive axes, with the third optical axis being parallel to the first absorption axis of the first polarization layer (1).

16. OPTICAL FILM FOR CONTROLLING AND RESTRICTING THE ANGLE OF VIEW RANGE OF AN OBSERVER, characterized by comprising: a first polarization layer (1) having a first absorption axis that is oriented at an angle of 0° to 30° from a surface normal of the optical film, at least one phase shift compensation layer to improve a restriction of the angle of view range, a second polarization layer (2) having a second absorption axis that is oriented parallel to a surface of the optical film, wherein between the first polarization layer (1) and the second polarization layer (2), i.e., in a first alternative, is disposed a first compensation layer (B*) (3), which is formed to be spatially homogeneous and made of a first biaxially birefringent material having two optical axes and three principal refractive axes,wherein the principal axes of refraction are in one-to-one correspondence with the refractive indices nx, ny, nz, wherein the principal refractive axis to which a minimum refractive index corresponds or the principal refractive axis to which a maximum refractive index corresponds is parallel to the first absorption axis, and wherein for the first compensation layer (B*) (3), a Petition 870250080945, dated 09 / 09 / 2025, page 122 / 132 11 / 12 thickness d of the first compensation layer (B*) (3), a phase shift Δph and a specified wavelength λ satisfy a condition: 2π . . Aph = -— d · I nx — ny | < 2π , Λ ii. in a second alternative, at least two compensation layers made of uniaxially birefringent materials are arranged,wherein a first “A*” compensation layer (4) which is formed to be spatially homogeneous is made of a first uniaxially birefringent material having a first optical axis and two first principal refractive axes which are different from each other, with the first optical axis being perpendicular or parallel to the first absorption axis of the first polarization layer (1), and when viewed in the direction of the observer behind it, a second “A*” compensation layer (5) which is formed to be spatially homogeneous is disposed, which is made of a second uniaxially birefringent material having a second optical axis and two second principal refractive axes, with the second optical axis being perpendicular to the first optical axis, wherein for each of the compensation layers, a thickness d of each of the compensation layers, an extraordinary refractive index ne and an ordinary refractive index no,A phase shift Δph and a specified wavelength λ satisfy a condition: 2π kph = —d |ne -n0| < 2tt, wherein, in both alternatives ie ii, the materials and thicknesses d of the compensation layers are specified such that, measured in a spherical coordinate system with its origin on a film surface and on a plane of the film surface, a luminance density is minimum only in a specified range of solid angles (R) Petition 870250080945, dated 09 / 09 / 2025, page 123 / 132 12 / 12 comprising: an azimuth φ with |φ| and |180° -φ| being less than an absolute value of a specified limiting azimuth φιim, measured relative to a preferred direction in the plane of the film surface, and a polar angle θ, whose absolute value is greater than a specified limiting polar angle θlim, measured relative to the surface normal, or measured relative to the first absorption axis and in a plane defined by the surface normal and the first absorption axis,if the first absorption axis is not parallel to the surface normal. Petition 870250080945, dated 09 / 09 / 2025, pp. 124 / 132.

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