Light guide and display screen using such a light guide

Abstract

The invention relates to a light guide (1) having two main faces. Each main face has at least one edge (3) around the main face, the main faces being connected at the edges (3) by side faces (8). The light guide comprises a plurality of three-dimensionally shaped light output coupling elements (4, 5) on at least one of the main faces and / or within a volume enclosed by the main faces and the side faces (8). The light output coupling elements (4, 5) are distributed according to a predetermined distribution pattern. Light coupled into the light guide (1) propagates by total internal reflection, unless it enters or impinges on an output coupling element (4, 5), and one of the two main faces is better for output coupling than the other. According to the invention, the plurality of output coupling elements (4, 5) is divided into groups of output coupling elements (4, 5), each group being complementary to each of the other groups. The members of each group have a common characteristic blaze angle (11) and a common characteristic output coupling property, which common characteristic output coupling property and blaze angle (11) are different from the characteristic output coupling properties and blaze angles (11) of the members of the other groups, which results in a different angular distribution of the output coupled light. This reduces the number of visible artefacts which can negatively affect the visual experience when the light guide (1) is used in a display.

Description

Technical Field

[0001] The present invention relates to a light guide having two main surfaces, each main surface having at least one edge surrounding it, the main surfaces being connected by side surfaces at these edges. The light guide includes a plurality of three-dimensional light output coupling elements on at least one of the main surfaces and / or within a volume enclosed by the main surfaces and the side surfaces. These light output coupling elements are distributed according to a predetermined pattern. The light guide further has at least 70% transparency so that light passes through the two main surfaces. Background Technology

[0002] The distribution pattern is predetermined so that light is coupled into the light guide on at least one of the sides and propagates through total internal reflection within the light guide (1) before entering or illuminating the output coupling element, such that the preferred of the two principal surfaces couples out a higher amount of light than the other of the two principal surfaces. For a given material and wavelength range of the light guide and for a given structure of the output coupling element, the distribution pattern is predetermined directly using a commercially available optical design program (such as Synopsys' LightTools "Backlight Pattern Optimization").

[0003] The output coupling element has a longitudinal section in a plane perpendicular to at least one of the principal surfaces. The longitudinal section is formed approximately as a polygon with at least three corners and at least three connecting lines connecting these corners. The term "approximately as a polygon" takes into account manufacturing defects: while a polygon is mathematically composed of a number of straight lines connected by an equal number of corners to form a closed polygonal loop, the longitudinal section of the output coupling element only resembles a polygon. Due to the manufacturing process, the shape of the connecting lines deviates from an ideal straight line, particularly in the corner regions where two connecting lines intersect, and may have a slight curvature; that is, the connecting lines may be slightly curved rather than straight. These corners are not sharp but rounded. One of the at least three connecting lines includes a selected line consisting of at least one straight line segment. The direction of the straight line segment relative to the plane of at least one principal surface is oriented to interfere with total internal reflection by refraction and / or reflection, and to define the blaze angle and thereby define the characteristic output coupling property in a manner that defines the first output coupling angle range. Therefore, the blaze angle determines the characteristic output coupling property within the first output coupling angle range. For most output coupling elements, each output coupling element is separated from any other output coupling element by at least one micrometer. Since it is virtually impossible to fabricate output coupling elements with truly straight lines and acute angles by photolithography or any other process, at least the corners are rounded. At least in the corner region, the straight line therefore deviates from its ideal form and exhibits curvature. Depending on the size of the output coupling element, these curvatures can constitute up to 20% of the line length, even in cases where the output coupling element size is extremely small. These defects caused by the manufacturing process are understood as the tolerances included by the term "straight line": however, even in the case of rounded corners, specifically, the line used to define the blaze angle includes at least one straight line segment. The blaze angle is then defined by the orientation of this straight line segment relative to the plane of at least one main surface.

[0004] This type of output coupling element is known in the present art and is typically implemented as a recess in other flat surfaces. For example, in US2018 / 0088270 A1, specifically in... Figure 5A typical embodiment is illustrated in A. However, in current applications, light guides using such or similar output coupling elements do not emit light homogeneously, even if the distribution of the output coupling elements is positively corrected for homogeneous illuminance. Light from the illumination source is typically coupled into the light guide on the sides. Near these sides, hot spots (bright spots separated by smaller dark areas) are identifiable when the light guide is visually inspected; these hot spots are linked along the sides or edges respectively. Furthermore, the light guide exhibits dispersion: in the case of multi-color illumination, brighter and darker bands forming a rainbow-like pattern extend on the main surface parallel to the edges and alternate in one direction on the main surface perpendicular to the edges. If this light guide is used in a display, the viewer's visual impression is disturbed. However, in the present art, no measures are disclosed for improving the visual impression by removing hot spots and dispersion artifacts.

[0005] EP 2 474 846 A1 discloses a diffractive light output coupling unit for forming part of a directional light output coupling system comprising a plurality of such output coupling units. The diffractive light output coupling unit includes a carrier element for accommodating a diffractive surface relief pattern and transmitting light. The diffractive surface relief pattern includes a plurality of successive diffractive surface relief forms defined on a predetermined surface of the carrier element. The diffractive surface relief pattern is configured to couple incident light thereon via an interaction involving at least two of the plurality of successive diffractive surface relief forms, in order to enhance the directionality of the coupled light to be output through collimation, wherein several rays of the diffracted incident light penetrate at least the first surface relief form during the interaction. No measures are taken to avoid the aforementioned artifacts.

[0006] EP 1 016 817 A1 discloses a light guide for providing backlight for a flat panel display using at least one light source, such that the light guide has a sponsoring surface comprising a specific pattern. These patterns have diffraction properties for guiding light in the direction of the display, and these patterns include uniformly distinct regions with a specific distribution on the surface of the light guide. The local output coupling efficiency of the light guide depends on the characteristic properties of the pattern, which depend on the distance from the light source or its wavelength. The possibility of artifacts such as hot spots and rainbow-like features, as mentioned above, is not discussed.

[0007] US 6,773,126 B1 describes an optical panel comprising a light source and a panel element operatively connected to the light source. The panel element comprises a substantially transparent light-transmitting material and operates as a waveguide panel, within which a light beam received from the light source propagates by total internal reflection. A diffraction output coupling system is disposed on the panel element above its optical surface and operates to output coupled light beams from within the panel element. The diffraction output coupling system comprises a plurality of local grating elements. These local grating elements have multiple configurations and are optimized such that diffraction efficiency varies with position. The artifacts mentioned above and the possibility of reducing or avoiding these artifacts are not discussed.

[0008] US 9,261,639 B1 discloses an optical display device including a light source, a pixelated display panel, and a light guide for collecting light from the light source and transmitting the light via total internal reflection. A first main surface of the light guide includes recessed regions having a circularly based profile (such as a quarter-circle profile) to reflect light from the light guide to the pixelated display panel. A first optical layer covering at least a portion of the first surface of the light guide fills the recessed regions contained in the first surface of the light guide. A second optical layer covering at least a portion of the second surface of the light guide transmits the reflected light to the pixelated display panel. Furthermore, artifacts, as mentioned above, are not the subject of this discussion.

[0009] Finally, WO 2019 / 087118 A1 describes a light distribution structure and related elements, such as light guides. This structure preferably includes an optically functional layer with at least one feature pattern, which is established in a light-transmitting carrier by means of a plurality of three-dimensional optical features that are variable in at least one of the following parameters: profile, size, periodicity, orientation, and their arrangement within the feature pattern. For example, the optical features are embodied in an internal optical cavity capable of establishing total internal reflection at its horizontal surface and at a substantially vertical surface. The possibility of artifacts such as hot spots and rainbow-like features, as mentioned above, is not discussed here.

[0010] In the known current technology, artifacts associated with the output coupling structure (such as hot spots and rainbow-like features) have not been given attention (if observed), and therefore no measures that can be applied to reduce or avoid such artifacts have been described.

[0011] Of course, coupling the light guide with additional optical layers (such as diffuser layers or prism sheets) would be possible. However, these measures would not only increase the thickness of the layer assembly incorporated into the display, but could also reduce brightness and / or angular illuminance distribution. Specifically, since the thickness of the layer assembly is becoming an increasingly important feature in today's applications, using additional layers would be a disadvantage. Summary of the Invention

[0012] Therefore, the object of the present invention, as described at the beginning, is to avoid or at least reduce artifacts such as hot spots or rainbow-like features, especially when light guides are used in display screens, without involving additional optical layers.

[0013] This objective is achieved by dividing a plurality of output coupling elements into at least two groups of output coupling elements. Each group is complementary to each of the other groups, meaning that a randomly selected output coupling element belongs to only one of the output coupling element groups. Members of each output coupling element group share a common characteristic blaze angle and therefore a common characteristic output coupling property, as mentioned at the beginning. The common characteristic blaze angle and common characteristic output coupling property differ from the characteristic output coupling properties and blaze angles of members of the other groups; that is, each output coupling element group has its own unique blaze angle and therefore unique output coupling property. This causes light to be output coupled at different angles to different output coupling element groups. Therefore, each output coupling element group is responsible for output coupling light at a specific angle distribution (specifically, within a first angular range). These different angular distributions of light are at least partially mixed to minimize or at least reduce, compared to current techniques, visual artifacts (specifically, rainbow-like features and hot spots) in the light characteristics of the output coupling.

[0014] Groups of different output coupling elements can have the same size, and each group can contain the same number of output coupling elements, but this is not a necessary condition, and these groups can contain different numbers of output coupling elements. In fact, these numbers can vary considerably. To improve the results, it is sufficient to define only two groups of output coupling elements, one of which contains 99% of all output coupling elements (i.e., the plurality of output coupling elements), and the other group contains only 1% of all output coupling elements. However, the results of avoiding visual artifacts can be further improved by assigning more output coupling elements to the other group. When the relationship between group sizes is predefined in the optimization procedure, this starts with groups having approximately the same number of elements.

[0015] The output coupling angle distribution consists at least of a first angular range, defined by its projection onto a plane of the longitudinal profile, but preferably consists of a second angular range, defined by its projection onto a principal plane. Both angular ranges represent specific output coupling properties. However, the second angular range is not dependent on the blaze angle, as will be further explained below. The size of the first angular range depends primarily on the angular spectrum of the incident light. All groups of output coupling elements differ at least in the first angular range, but preferably, the groups of output coupling elements differ in both the first and second angular ranges. This allows for, and even better reduces, artifacts compared to differences only in either the first or second angular range.

[0016] As mentioned at the beginning, the longitudinal profile is formed approximately as a polygon with at least three corner angles and an equal number of connecting lines. In an advantageous embodiment, the approximate polygon has exactly three corner angles connected by three connecting lines. Furthermore, the term "formed approximately as a polygon" refers to an ideal form and includes tolerances due to manufacturing defects. At the microscale, surface roughness between 5 nm and 10 nm is possible. The first connecting line is a baseline having straight line segments located in a plane parallel to one of the principal surfaces. The second connecting line is configured to form an angle between 75° and 90° with the first connecting line, preferably between 85° and 89°, and specifically 88°. Finally, a third connecting line of selected lines connects the distal ends of the first and second connecting lines. The third connecting line defines the characteristic output coupling properties by enclosing a scintillation angle with the first connecting line. Each of the first and third connecting lines, and preferably the second connecting line, includes at least one straight line segment having a length generally at least 60% of the total length of the line, the straight line segment extending to both sides of the center of the respective line. However, due to manufacturing reasons, the second connecting line may actually be formed as an "S"-shaped curb with a very slight curvature along most of the line, making it difficult to define the straight line segments. To properly define the second connecting line and, specifically, its angle with the first connecting line in this case, it is approximated by an approximate straight line corresponding to the tangent taken at the center of the second connecting line. Optical guides including output coupling elements of this shape are easier to manufacture than those with curved connecting lines. However, considering the aforementioned manufacturing defects, these connecting lines may be approximated in the optimization process using an exponential or polynomial function of up to the fifth order. In either case, there may be deviations from the straight line within a predetermined tolerance due to manufacturing defects.

[0017] The three-dimensional shape of each of the output coupling elements in each group is defined by a partial rotation of a longitudinal section in a plane perpendicular to the longitudinal section around a central axis parallel to the longitudinal section but outside the longitudinal section, with a rotation angle other than 0°, preferably between 5° and 25°. If the longitudinal section has the shape of a right triangle, then the central axis is in particular parallel to the second connecting line.

[0018] The rotation angle essentially defines the size of the second angular range, while the blaze angle essentially determines the first angular range, which further depends on the angle of light incident on the surface defined by the third connecting line. Specifically, the blaze angle differs for different groups of output coupling elements. For example, while the blaze angle is 53° in the first group, it might be 57° in the second group. Both groups may contain approximately the same number of output coupling elements. In another embodiment, the first group includes output coupling elements with a standard blaze angle of 55°, which is particularly useful for optimizing the angular distribution in light guides used in the automotive industry. Other groups contain output coupling elements with blaze angles that are preferably symmetrically distributed around the standard blaze angle of 55° (for example, 54° and 56°, or 53° and 57°, in the second and third groups, respectively). Further groups of output coupling elements may be defined in a total of five groups, for example, with deviations of -3°, -2°, 0°, 2°, and 3° around the standard blaze angle (not necessarily 55°). Each of these groups may contain approximately 20% of all output coupling elements.

[0019] It is also possible to provide output coupling elements in at least one group of output coupling elements, so that, for at least one of these groups of output coupling elements, the scintillation angle varies continuously or discretely between the two end positions of the partial rotation. Besides the fact that this helps to further improve artifact reduction, this particular embodiment is also useful from the manufacturer's perspective: by using output coupling elements with varying scintillation angles, it is possible to use only one group of output coupling elements that is easier to manufacture. This is a specific case of the invention, in which only two groups of output coupling elements are implemented, but the second group has no members because it is an empty group. In practice, only one group exists. However, this particular embodiment also effectively reduces artifacts when applied to one or more groups of output coupling elements.

[0020] Light guides are typically made of transparent thermoplastic or thermoelastic materials, or glass. The output coupling elements typically have a maximum size of 100 μm in each spatial direction, preferably between 1 μm and 30 μm. This prevents the output coupling elements themselves from becoming visible to the observer when using light guides. Furthermore, if the size of each output coupling element is smaller than a subpixel of the LC panel, several output coupling elements can cover the subpixel, which helps reduce or even avoid so-called color flicker.

[0021] At least one of the output coupling elements in at least one group of output coupling elements protrudes or extends into the at least one of the autonomous surfaces. Alternatively or in combination, the output coupling elements may also be shaped into microprisms. Furthermore, the output coupling elements in at least one group of output coupling elements may be formed as cavities recessed inward within the light guide. In this case, these cavities are evacuated or filled with a material having a refractive index and / or haze value different from the refractive index or haze value of the material of the light guide, respectively. In the case of refractive index, the refractive index inside the cavity is preferably lower than the refractive index outside the cavity in the light guide, and in the case of haze value, the haze value inside the cavity is preferably higher than the haze value outside the cavity in the light guide. Each group of output coupling elements may, of course, be implemented in different ways. For example, a first group of output coupling elements may extend into one of the autonomous surfaces, a second group may be shaped as a microprism protruding from one of the autonomous surfaces, and a third group includes output coupling elements formed as cavities. If the light guide is a component within a stack of other optical layers, it is of course advantageous to keep the height of the light guide in the stack as small as possible, and preferably to extend the output coupling elements, which are easier to manufacture than the cavity within the light guide, into the main surface, since these output coupling elements can be applied after the light guide has been fabricated.

[0022] The distribution pattern of the output coupling elements on at least one main surface and / or within the volume of the light guide is preferably predetermined so that the output light is coupled on at least one of the two main surfaces with an illuminance uniformity of at least 60%, preferably 70% or more. With this white uniformity, artifacts are no longer visible as interference to users of devices equipped with this light guide. The distribution pattern can be predetermined using commercially available optical simulation programs (such as the "Backlight Pattern Optimization" module from Synopsys' optical modeling tool), which may include conditions such as inputs for optimization. Illuminance uniformity is measured using a nine-point procedure with a camera vertically positioned above the main surface at a distance of 90 cm. For reference, see Chapter 8 of the Measurement Standards for Information Displays published by the International Committee for Display Metrology (Revision 1.03, June 1, 2021).

[0023] For example, a distribution pattern can be selected such that near the side where light is coupled into the light guide (assuming two groups of output coupling elements are used), the elements from both groups are provided equally in a relationship of approximately 50% to 50%, and as the distance from this side increases, the elements from one group become more dominant than those from the other, thus continuously increasing to a relationship of 100% to 0%. This will increase the overall illuminance of the display incorporated into such a light guide in a predetermined viewing angle region. By selecting the distribution pattern in this way, it is also possible to take into account that the angular spectrum of light coupled into the light guide may vary between the side coupled with the input light and the side opposite to that side.

[0024] Furthermore, each of the output coupling elements contributes more or less to the overall haze of the light guide. In a preferred embodiment, (i) the distribution pattern of the output coupling elements on at least one main surface and / or within the volume of the light guide, (ii) the number of output coupling elements, and (iii) their dimensions are predetermined to produce an average haze of 30% or less on at least 50% of one of the main surfaces. Here, the haze value is measured according to Procedure A of ASTM D 1003-13.

[0025] The present invention also relates to a display screen comprising a light guide as described above. In addition to the light guide, the display screen includes one or more light sources whose emission couples light into the light guide at least at one of their sides. The display screen further includes a transmissive display panel located in front of the light guide and visible from the observer's viewing angle. The transmissive display panel and the light guide are typically separated only by an air layer or optically bonded to each other; in most cases, no other optical layer is disposed between the display panel and the light guide.

[0026] The light guide includes an output coupling element, and typically, transmissive display panels include pixels. In this case, the spatial extension of the output coupling element is smaller than the spatial extension of a pixel in each dimension of Cartesian space to further increase uniformity and reduce or even eliminate contrast or color flicker. If the transmissive display panel includes pixels composed of subpixels, then the spatial extension of the output coupling element is preferably smaller than the spatial extension of a subpixel in each dimension of Cartesian space.

[0027] It should be understood that the features previously mentioned, as well as those to be explained below, apply not only to the combinations described, but also to different combinations or individually, without departing from the framework of the invention set forth herein. Attached Figure Description

[0028] The invention will be explained in more detail below with reference to the accompanying drawings, which also illustrate essential and other features of the invention. Specific examples shown in the drawings are for illustrative purposes only and should not be construed as limiting the invention to these drawings. For example, the description of specific examples having multiple elements or components should not be interpreted in the sense that all of these elements or components must be present to carry out the invention. In fact, different specific examples may include alternative elements or components, fewer elements or components, or additional elements or components. Unless the contrary is explicitly mentioned, elements or components of different specific examples may be combined with each other. Modifications and variations described with respect to one of these specific examples may also apply to other specific examples. To avoid repetition, the same elements or related elements in different drawings are given the same element reference numerals and are not explained again. In the drawings,

[0029] Figure 1 The light guide shown in the bottom view.

[0030] Figure 2 Showing a cross-section through the light guide,

[0031] Figure 3 A) to Figure 3 C) Demonstrate an output coupling element with an idealized shape.

[0032] Figure 4 A) to Figure 4 C) Demonstrating the output coupling element manufactured using photolithography.

[0033] Figure 5 A) Figure 5 B) Show two output coupling elements with different first angle ranges.

[0034] Figure 6 A) Figure 6 B) Display Figure 6 Output coupling elements with different second angle ranges, and

[0035] Figure 7 A display with light guides is shown. Detailed Implementation

[0036] Figure 1 Light guide 1 is shown, which has two principal faces: a bottom principal face and a top principal face. The bottom principal face 2 is shown here; however, in other configurations, this could also be the top principal face. Each principal face has at least one edge surrounding it. Figure 1 In this embodiment, the bottom main surface 2 and the top main surface have four edges 3 surrounding these main surfaces. The shape of the edges 3 surrounding the light guide 1 depends primarily on the purpose of using the light guide 1. For example, in an ATM or laptop computer, the shape would mostly look similar to Figure 1The shape shown is not explicitly stated. However, in automobiles, the shape must more or less follow a design with rounded edges or edges of different shapes. In the illustrated embodiment, the light guide 1 is plate-shaped, with two planar and parallel main surfaces. In other specific examples, the main surfaces may have curvature and / or may form a wedge shape. At edge 3, the main surfaces are connected by side surfaces, which... Figure 1 The embodiment shown is configured perpendicular to the plane of the paper. The light guide 1 has at least 70% transparency so that light passes through the light guide via the two main surfaces.

[0037] The light guide 1 includes at least one of multiple three-dimensional light output coupling elements 4 and 5 on its main surface. Figure 1 In this embodiment, the optical output coupling elements 4 and 5 are located only on the bottom main surface 2. Other specific examples of the light guide additionally or alternatively include optical output coupling elements 4 and 5 on the top main surface. Additionally or alternatively, the plurality of optical output coupling elements 4 and 5 may also be provided within a volume enclosed by the main surface and the sides. For most of the output coupling elements 4 and 5, any one output coupling element 4 and 5 is separated from any other output coupling element 4 and 5 by at least one micrometer. The output coupling elements 4 and 5 have a longitudinal profile in a plane perpendicular to the bottom main surface 2. The longitudinal profile is formed as approximately a polygon with three corners and three connecting lines connecting these corners. One of the three connecting lines is a selected line, which, if not straight over its entire length, includes at least one straight line segment. As will be further explained below, the orientation of the straight line segment relative to the bottom main surface 2 defines the blaze angle and thereby defines the characteristic output coupling properties in a manner that interferes with total internal reflection by refraction and / or reflection and defines a first output coupling angle range.

[0038] The plurality of output coupling elements 4 and 5 are divided into several groups of output coupling elements 4 and 5. Each group is complementary to each of the other groups, and the members of each group have a common characteristic blaze angle and therefore at least one common characteristic output coupling property, which differs from the characteristic output coupling properties and blaze angles of the members of other groups. As a result, depending on the group to which each output coupling element belongs, light is output coupled at different angular distributions. Figure 1 In a specific example, there are two groups of output coupling elements: a first group with a first output coupling element 4 and a second group with a second output coupling element 5. However, it is also possible to implement more than two groups of output coupling elements in the light guide 1.

[0039] The optical output coupling elements 4 and 5 (or, in short, the output coupling elements 4 and 5) are distributed according to a pattern predetermined, for example by a commercially available optical design procedure as mentioned above, so that light is coupled into the light guide 1 on at least one of the sides and propagates within the light guide 1 by total internal reflection before entering or illuminating the output coupling elements 4 and 5, such that the preferred of the two principal surfaces couples out a higher amount of light than the other of the two principal surfaces. For total internal reflection, the light must be coupled into the light guide only within a limited angular range.

[0040] The optical output coupling elements 4 and 5 are located on the bottom main surface 2. Figure 1 In the specific example shown, the top master surface is preferably coupled with a higher amount of light output than the bottom master surface 2. Figure 2 The image shows this situation in more detail, illustrating the passage through something similar to... Figure 1 The cross-section of optical guide 1. However, in Figure 2 For the sake of better understanding, output coupling elements 4 and 5 are configured equidistant from each other; however, this is not the case in reality. Figure 1 Relatedly, this section will be perpendicular to the plane of the paper and run from bottom to top, corresponding to Figure 2 From left to right in the middle. Figure 2 On the upper left side, a light source 6 is configured to emit light along the beam 7, and these beams pass through the side 8 and enter the light guide 1. (Regarding...) Figure 1 This side surface 8 will be located at the lower edge 3 of the bottom main surface 2. It should be noted that the light source 6 does not emit a single beam of light; rather, it emits light along the main portion of the side surface. Figure 2 The light beams 7 (solid beams, dashed beams, and dotted-dashed beams) are symbolized by several beams 7 corresponding to different depths perpendicular to the plane of the paper. It should be further noted that beams 7 are emitted within a small angular range, which allows light to propagate through the light guide 1 without coupling to the output in the absence of output coupling elements 4 and 5, because the angular spectrum is limited by the angle that allows light to undergo total internal reflection at the principal plane of the plane. The side opposite the light source 6 may typically have a reflective coating to minimize light loss.

[0041] However, due to the presence of the first output coupling element 4 and the second output coupling element 5, light will be coupled out from the light guide 1. A solid line beam 7 enters the light guide 1 at the side 8. This solid line beam undergoes total internal reflection at the leftmost output coupling element 4, also represented by a solid line. The light is reflected at a certain angle, allowing it to pass through the top principal surface of the light guide 1 and exit at a predetermined angle. The same applies to the dashed line beam 7 reflected at another first output coupling element 4, located deeper within the light guide 1, as seen from the plane of the paper. Finally, the beam 7, shown as a dotted line, is reflected at the second output coupling element 5, which, in terms of the depth dimension of the light guide 1, is located between the other two light output coupling elements 4 within the light guide 1. However, the second output coupling element 5 has a slightly different shape than the first output coupling element 4. Therefore, the reflection angle is different compared to the light reflected at the first output coupling element 4, and the dotted line beam 7 exits the light guide at a different angle. Together with the predetermined distribution of the output coupling elements, this helps to reduce artifacts such as hot spots or rainbow-like features.

[0042] The optical output coupling elements 4 and 5 typically have a maximum size of 100 μm in each spatial direction, but preferably, their maximum size is between 1 μm and 30 μm. Although in Figure 1 and Figure 2 In the specific example shown, these optical output coupling elements are formed as recesses and thus extend into the bottom main surface 2, but these output coupling elements may also be formed on both main surfaces or as cavities recessed inward within the light guide. These optical output coupling elements may also be formed as protrusions and / or shaped into microprisms. If the output coupling elements are formed as cavities, these cavities are evacuated or filled with a material having a refractive index and / or haze value different from that of the material of the light guide 1. The light guide 1 may be made of a thermoplastic material (e.g., PMMA, polycarbonate, PMMI) or glass. It is also possible that at least two groups of output coupling elements include different types of output coupling elements. For example, a first group of output coupling elements may include output coupling elements formed as protrusions on at least one of the main surfaces, a second group of output coupling elements formed as cavities recessed inward within the light guide 1, and a third group of output coupling elements formed as recesses on at least one of the two main surfaces.

[0043] exist Figure 1 In the specific example shown, the distribution pattern of the output coupling elements 4, 5 on the bottom main surface 2, on at least one of the two main surfaces, and / or within the volume of the light guide 1 is preferably predetermined so that the output light is coupled with at least 60% illuminance uniformity by means of the output coupling elements 4, 5 on at least one of the two main surfaces (here, the top main surface).

[0044] Preferably, each of the output coupling elements 4 and 5 contributes to the overall haze of the light guide 1, and the distribution pattern, number, and size of the output coupling elements 4 and 5 on the bottom main surface 2 are predetermined to produce an average haze of 30% or less on at least 50% of the top main surface (i.e., on the surface opposite to where the output coupling elements 4 and 5 are positioned). In this way, each of the output coupling elements contributes to the overall haze of the light guide 1. For example, the haze can be measured according to ASTM D 1003-13.

[0045] The output coupling elements 4 and 5 will be described in more detail below. Figure 3 Output coupling elements 4 or 5 with idealized shapes are shown. Figure 3 A) shows a perspective view of the output coupling element. Figure 3 B) Shows a projected view from the top or bottom, and Figure 3 C) shows along the Figure 3 The longitudinal cross-section of coupling elements 4 and 5 obtained by the dashed lines marked in B).

[0046] Longitudinal section always means along such Figure 3 B) shows the plane (i.e., along the direction consistent with the shortest distance between the entry and exit points, along...). Figure 3 The dashed line in B) passes through the cross-section of the output coupling element, minimizing the area of ​​the cross-section. Because in Figure 3 In B), the curve of the projected output coupling element has the shape of an arc with a common center point, so the cross-sectional plane cuts out two arcs perpendicular to its tangent.

[0047] However, due to limitations in the manufacturing process (for example, forming optical tools using optical lithography and producing light guides using nanoimprinting and / or injection molding processes), the fabrication of such... Figure 3 A) to Figure 3 The ideal structure shown in C) is quite difficult to achieve. Therefore, the actual structures of the output coupling elements 4 and 5 deviate more or less from this ideal shape and look more like... Figure 4 A) to Figure 4 The shape shown in C). Specifically, the corners are rounded, as in Figure 4 This can be seen in the longitudinal section shown in C).

[0048] Generally, each output coupling element 4, 5 has, for example, in a plane perpendicular to at least one of the main plane, the following configuration: Figure 3 C) or Figure 4 C) shows a longitudinal section, wherein the longitudinal section is formed approximately as a polygon having at least three corners and at least three connecting lines connecting these corners, the connecting lines being either curved or straight. Figure 3 The longitudinal section in C) has three corners connected by straight lines. On the other hand, in Figure 4 The more realistic longitudinal section shown in C) has rounded corners. The basic polygon can be defined in two ways with respect to optical effects, since this effect (as will be further elaborated below) does not depend on the actual shape of the corners. The first possibility is to extend the straight line or segments of the straight line further until they intersect each other, thus producing a shape as shown in... Figure 3 The shape shown in C) is a second possibility. The rounded corner can be approximated by a large number of short straight lines. Within the limit of infinitely short lines, the rounded corner can be approximated by a function (e.g., a polynomial function). Figure 4 In the longitudinal section shown in C), the output coupling elements 4 and 5 are formed as recesses in the light guide 1, wherein the plane of the bottom main surface 2 is perpendicular to the paper plane and contains the horizontal baseline 9 of the output coupling elements 4 and 5 (relative to the paper plane). Output coupling elements protruding from the main surface will have the same shape. When the output coupling elements are within the volume of the light guide 1, the two lower corners will have concave shapes, which are located in... Figure 4 C) has a convex shape as seen in the self-output coupling element.

[0049] exist Figure 3 and Figure 4 The output coupling elements 4 and 5 have a longitudinal profile, which is formed in Figure 4 The shape approximates only a polygon with three corners. These corners are connected by connecting lines. The first connecting line is a baseline 9 located in a plane parallel to one of the main faces (here, the bottom main face 2). In the case where the output coupling element is formed as a recess, the first connecting line is a straight line; in other specific examples, the first connecting line includes at least one straight line segment.

[0050] The second connecting line 12 is configured at an angle between 75° and 90° to the baseline 9. Figure 3 and Figure 4 In the illustrated embodiment, the angle is 90°. However, practice has shown that it is preferable to choose an angle less than 90°, specifically in the range of 85° to 89° (e.g., 88°). In any case, the angle should be chosen such that light cannot illuminate the surface defined by the rotation of the second connecting line 12. In reality, the second connecting line may exhibit a slight curvature and have an "S" shape, where the deviation from the straight line form, which can be considered as surface roughness, is in the range of 5 nm to 10 nm. The angle is then determined as explained above.

[0051] The third connecting line 13 connects the baseline 9 and the distal end of the second connecting line 12. The third connecting line 13 is a selected line and defines the characteristic output coupling properties by its enclosure scintillation angle 11 with the baseline 9. If the third connecting line 13 is curved, the straight segment 10 included in the third connecting line preferably has a length of at least 60% of the total length of the third connecting line 13. A length less than 60% will also be effective; however, efficiency will decrease slightly. Figure 1 and Figure 2 In the case of the output coupling elements 4 and 5 formed as recesses in the light guide 1, the output coupling is achieved by reflecting light at line 13 or line segment 10 respectively, after which the light can pass through the main surface on the opposite side and leave the light guide 1.

[0052] The orientation of the line segment 10 or the line relative to at least one principal surface (here, the bottom principal surface 2) is used to interfere with total internal reflection by means of reflection and / or refraction of light illuminating individual surfaces including the line segment 10, and to define the blaze angle 11 and thereby define the characteristic output coupling property in a manner that defines the first output coupling angle range as the characteristic output coupling property. In other words, the output coupling angle range is directly related to and depends on the orientation of the line or the line segment 10 relative to the plane of the principal surface, respectively.

[0053] In this specific example, the three-dimensional shape of each of the output coupling elements 4 and 5 is defined by a partial rotation of the longitudinal profile in a plane perpendicular to the longitudinal profile about a central axis parallel to but outside the longitudinal profile. Another possibility is to define the three-dimensional shape by translation of the longitudinal profile. The rotational definition of the third connecting line 13... Figure 2 The beam 7 is reflected at its location or refracted in other specific examples onto a plane. The rotation angle differs from 0°, and is preferably within a range of 5° to 25°, encompassing these angles. This can be seen in... Figure 3 A) and Figure 4 In diagram A), these figures show perspective views of output coupling elements 4 and 5, and Figure 5 Two embodiments of output coupling elements with different partial angles are shown. Figure 5 A) shows a bottom view of the first output coupling element 4, i.e., the viewing direction along the interior of the light guide 1 from the bottom main surface 2. Figure 5 B) shows a bottom view of the second output coupling element 5. The central axis is marked by a cross and oriented perpendicular to the plane of the paper. The partial rotation angle of the first output coupling element 4 is 25°, which is greater than the partial rotation angle of the second output coupling element 5, which is 15°. Furthermore, the arc of the reflective surface of the second output coupling element 5 has a stronger curvature than the arc of the first output coupling element 4 because its radius (i.e., the distance to the central axis) is shorter for the second output coupling element 5.

[0054] exist Figure 3 and Figure 4 In the illustrated embodiment, the longitudinal profile always has the same shape, regardless of the position of the section being cut. Therefore, the blaze angle 11 is constant across the individual output coupling elements. However, it is also possible to combine partial rotation with discrete or continuous variation of the blaze angle 11 with the rotation angle, meaning the shape of the longitudinal profile depends on the position relative to the rotation. The blaze angle 11 can vary continuously or discretely between the two end positions of the partial rotation (for example, between 53° and 57°). In an advantageous embodiment, the blaze angle varies for at least one group of output coupling elements. This helps to further reduce artifacts and essentially allows the use of only one group of output coupling elements, which is easier to manufacture.

[0055] As previously mentioned, the light guide includes a plurality of output coupling elements divided into at least two complementary groups of output coupling elements. In a specific example related to the figures, the plurality of output coupling elements are divided into two groups, each group having members with a common characteristic blaze angle 11 and therefore a common characteristic output coupling property, which differs from the characteristic output coupling property and blaze angle of the members of the other group. This causes light to be output coupled at different angles to different groups of output coupling elements. In the specific example discussed above, the output coupling angle distribution includes a first angular range and a second angular range. The latter is defined by projection onto the principal plane. Figure 5 A) shows the first output coupling element 4, while Figure 5 B) illustrates the second output coupling element 5. The second angle range is defined by partial rotation angles corresponding to the dimensions of each segment, representing a complete 360° rotation relative to the formation of the donut shape. These partial rotation angles directly relate to the second angle range and define the second characteristic output coupling property, which is independent of the blaze angle 11. While the blaze angle 11 must be different for different groups of output coupling elements 4 and 5, the partial rotation angles and therefore the second characteristic output coupling property may be the same for all groups.

[0056] The output coupling angle distribution further includes a first angle range defined by projection onto the plane of the longitudinal profile. Figure 6 A) shows the first output coupling element 4, while Figure 6 Section B) illustrates the second output coupling element 5. (See section regarding...) Figure 2 The light enters the optical guide 1 at different angles within a finite angular spectrum. The beam of light within this angular spectrum is ultimately reflected on the plane defined by the rotation of the third connecting line 13, as described above. Figure 3 and Figure 4Explanation. The individual first angular ranges are shown as shadow cones and differ when measured relative to baseline 9. Light incident on the surface defined by the rotation of the third connecting line 13 along the horizontal direction (relative to the plane of the paper) is reflected in the direction of the equally divided shadow cones. The first angular range is directly related to the flare angle 11, which defines the inclination of the third connecting line 13 or its straight segment 10, and thus the inclination of the plane of the reflected beam, as shown in the diagram. Figure 6 A) and Figure 6 B) It is evident that the first angular range defines the first characteristic output coupling property, which is the same for members of the same output coupling element group, but different for members of different output coupling element groups.

[0057] Figure 7 A display screen including the light guide 1 as described above is shown. The display screen further includes one or more light sources 6 that emit light that is coupled into the light guide 1 at least at one of the sides 8 (here, the upper left side 8). As seen from the observer's perspective, the transmissive display panel 14 is located in front of the light guide 1. Figure 7 In the specific example shown, the transmissive display panel 14 and the light guide 1 are separated only by an air layer 15, and there are no other optical elements disposed between the transmissive display panel 14 and the light guide 1. Alternatively, it is also possible to optically bond the transmissive display panel 14 to the light guide 1 using a highly transparent adhesive with a refractive index suitable for the light guide 1 to minimize reflection, whereby the refractive index of the bonding material must be lower than that of the material constituting the light guide 1 to allow total internal reflection within the light guide 1. Avoiding the use of additional optical layers minimizes the potential loss of display brightness, which is important in bright environments.

[0058] When the light guide 1 is used with a transmissive display panel 14 that includes pixels or pixels that are themselves composed of subpixels, the spatial extension of the output coupling elements 4 and 5 is preferably smaller than the spatial extension of the pixel or subpixel in each dimension of Cartesian space (i.e., in each of the three spatial directions).

[0059] The light guide 1 described above enhances the viewer’s viewing experience when used with the transmissive display panel 14 because artifacts such as hot spots or rainbow-like features are significantly reduced compared to transmissive display panels with light guides as known in the present art.

[0060] [List of Labels in the Attached Image]

[0061] 1. Optical guide

[0062] 2. Bottom Main Surface

[0063] 3. Edge

[0064] 4 Optical output coupling element / Output coupling element / First output coupling element / Coupling element

[0065] 5 Optical output coupling element / Output coupling element / Second output coupling element / Coupling element

[0066] 6. Light source

[0067] 7 beams

[0068] 8. Side view

[0069] 9. Horizontal baseline / baseline / connecting line

[0070] 10. Segmentation of a straight line

[0071] 11 Shining Angle / Common Trait Shining Angle / Special Trait Shining Angle

[0072] 12 Second connecting line / connecting line

[0073] 13 Third connecting line / straight line / connecting line

[0074] 14 Transmissive display panel

[0075] 15. Air layer.

Claims

1. A light guide (1) having two main surfaces, each main surface having at least one edge (3) surrounding the main surface, the main surfaces being connected by side connections at these edges (3), the light guide (1) comprising a plurality of three-dimensional optical output coupling elements (4, 5) distributed according to a predetermined distribution pattern, wherein: The light guide (1) has at least 70% transparency so that light passes through the two main surfaces. The distribution pattern is predetermined, and the light coupled to the light guide (1) on at least one of these sides (8) is designed to propagate by total internal reflection inside the light guide (1) before entering or illuminating the light output coupling elements (4, 5). The distribution pattern causes the preferred one of the two main surfaces to couple out a higher amount of light than the other of the two main surfaces. These optical output coupling elements (4, 5) have a longitudinal section in a plane perpendicular to at least one of these principal surfaces, the longitudinal section being formed as an approximate polygon having at least three corners and at least three connecting lines (9, 12, 13) connecting these corners, wherein one of the at least three connecting lines (9, 12, 13) includes a selected line of at least one straight line segment (10). The direction of the straight line segment (10) relative to the plane of at least one of the principal surfaces is oriented to interfere with total internal reflection by refraction and / or reflection, and to define the first output coupling angle range, thereby defining the blaze angle (11) and the characteristic output coupling property. For most of these optical output coupling elements (4, 5), any optical output coupling element is separated from any two adjacent optical output coupling elements by at least one micrometer. The feature is that the plurality of optical output coupling elements (4, 5) are divided into several groups of optical output coupling elements (4, 5), each group being complementary to each of the other groups, and the members of each group having a common characteristic blaze angle (11) and therefore a common characteristic output coupling property, wherein the optical output coupling elements (5) of one group are located between two other optical output coupling elements (4) of another group in the light guide (1), the common characteristic blaze angle (11) and the common characteristic output coupling property being different from the characteristic blaze angle (11) and output coupling property of the members of these other groups, thereby causing the light to be distributed and output coupled at different angles for different groups of optical output coupling elements (4, 5).

2. The optical guide (1) according to claim 1, wherein, The output coupling angle distribution consists of the following: a first angle range defined by the projection onto the plane of the longitudinal section and a second angle range defined by the projection onto the main surface.

3. The optical guide (1) according to claim 1 or 2, wherein, The longitudinal profile is formed as a polygon having three corners connected by three connecting lines (9, 12, 13), the first connecting line having a baseline (9) of straight line segments in a plane parallel to one of these principal planes, the second connecting line (12) being configured at an angle between 85° and 90° to the first connecting line, and the third connecting line (13) connecting the far ends of the first connecting line and the second connecting line (12), wherein the third connecting line (13) is the selected line and defines the characteristic output coupling property by means of the flare angle (11) enclosing the first connecting line.

4. The optical guide (1) according to claim 3, wherein, The three-dimensional shape of each of these optical output coupling elements (4, 5) is defined by a portion of the longitudinal profile rotating around a central axis that is parallel to the longitudinal profile but outside the longitudinal profile, with a rotation angle different from 0°.

5. The optical guide (1) according to claim 4, wherein, For at least one group of optical output coupling elements, for at least one of these groups of optical output coupling elements (4, 5), the blaze angle (11) varies continuously or discretely between the two end positions of the partial rotation.

6. The optical guide (1) according to claim 1 or 2, wherein, These optical output coupling elements (4, 5) have a maximum size of 100 µm in each spatial direction.

7. The optical guide (1) according to claim 1 or 2, wherein, The distribution pattern of these light output coupling elements (4, 5) on the at least one main surface and / or within the volume of the light guide (1) is predetermined so that the output light is coupled with at least 60% illuminance uniformity on at least one of the two main surfaces by means of these light output coupling elements (4, 5), the illuminance uniformity being measured by a nine-point procedure.

8. The optical guide (1) according to claim 1 or 2, wherein, Each of these optical output coupling elements (4, 5) contributes to the overall haze of the light guide (1), and wherein (i) the distribution pattern of these optical output coupling elements (4, 5) on at least one main surface and / or within the volume of the light guide (1), (ii) the number of optical output coupling elements (4, 5) and (iii) their size are predetermined to produce an average haze of 30% or less on at least 50% of one of these main surfaces, the haze being measured according to ASTM D1003-13.

9. The optical guide (1) according to claim 1 or 2, wherein, At least one group of optical output coupling elements (4, 5) protrudes or extends from at least one of the main surfaces into said at least one and / or is shaped into a microprism.

10. The optical guide (1) according to claim 1 or 2, wherein, At least one group of optical output coupling elements (4, 5) are formed as cavities recessed inward within the light guide, the cavities being emptied or filled with a material having a refractive index and / or haze value that are different from the refractive index or haze value of the material of the light guide (1).

11. A display screen comprising: The optical guide (1) according to any one of claims 1 to 10; One or more light sources (6) emit light, which is coupled to the light guide (1) at least at one of these sides (8); and A transmissive display panel (14) is located in front of the light guide (1) and is visible from the observer's perspective.

12. The display screen according to claim 11, wherein, The transmissive display panel (14) includes pixels, and the light guide (1) includes light output coupling elements (4, 5), wherein the spatial extension of these light output coupling elements (4, 5) is less than the spatial extension of a pixel in each dimension of Cartesian space.

13. The display screen according to claim 12, wherein, The transmissive display panel (14) includes pixels composed of subpixels, and the light guide (1) includes light output coupling elements (4, 5), wherein the spatial extension of these light output coupling elements (4, 5) is less than the spatial extension of the subpixel in each dimension of Cartesian space.

14. The display screen according to any one of claims 11 to 13, wherein, The transmissive display panel (14) and the light guide (1) are separated or optically joined only by an air layer (15).

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