Light guide and display screen using the same

Abstract

The present invention relates to a light guide (1) having two main surfaces, each of which has at least one edge (3) surrounding it and which are connected at the edges (3) by lateral surfaces (8). The light guide comprises a plurality of three-dimensionally shaped light output elements (4, 5) in at least one of the main surfaces and / or in a volume enclosed by the main surfaces and the lateral surfaces (8). The light output elements (4, 5) are distributed according to a predetermined distribution pattern. Light coupled into the light guide (1) is propagated by total internal reflection unless it is incident on an output element (4, 5) and one of the two main surfaces is preferred over the other in terms of output coupling. According to the invention, the plurality of output elements (4, 5) are divided into several output element (4, 5) groups, each group being complementary to each of the other groups. Each group member has a common characteristic blaze angle (11) and a common characteristic out-coupling characteristic that differs from the characteristic out-coupling characteristics and blaze angles (11) of the other members of the group, causing light to be out-coupled with a different angular distribution, thereby reducing the number of visible artifacts that may adversely affect the viewing 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 the main surface, the main surfaces being connected by a lateral surface at the edge. The light guide includes a plurality of three-dimensional light output elements within at least one of the main surfaces and / or within a volume surrounded by the main surfaces and the lateral surfaces. The light output elements are distributed according to a predetermined distribution pattern. The light guide further has a transparency of at least 70% with respect to light passing through the light guide through the two main surfaces.

Background Art

[0002] The distribution pattern is coupled to the light guide on at least one of the lateral surfaces and is predetermined such that, for light propagating within the light guide by total internal reflection before being incident on the output elements, one of the two main surfaces preferentially couples and outputs a higher amount of light than the other of the two main surfaces. For a given material and wavelength range of the light guide and a given structure of the output elements, the distribution pattern is directly predetermined using a commercially available optical design program (e.g., the "Backlight Pattern Optimization" of the Light Tools of Synopsys).

[0003] The output element has a longitudinal cross-section in a plane perpendicular to at least one of the main surfaces. The longitudinal cross-section is formed into a substantially polygon having at least three corners and at least three connecting lines connecting the corners. The term "substantially polygon" takes into account manufacturing defects. A polygon is mathematically composed of several straight lines, the straight lines are connected by an equal number of corners, and a closed polygon circuit is formed, but the longitudinal cross-section of the output element only resembles a polygon. Due to the manufacturing process, the shape of the connecting line deviates from an ideal straight line, especially in the corner region where two connecting lines intersect, and has a slight curvature. That is, the connecting line may not be a straight line but a slightly curved line. The corners are not sharp but rounded. One of the at least three connecting lines includes a selected line of at least one straight line segment. The orientation of the straight line segment with respect to the plane of at least one main surface defines a blaze angle so that total reflection is interfered with by refraction and / or reflection and a first output coupling angle range is defined, thereby defining characteristic output coupling characteristics. Therefore, the blaze angle determines the first output coupling angle range as characteristic output coupling characteristics. For most output elements, any output element is at least 1 μm away from any other output element. Since it is almost impossible to manufacture an output element with a true straight line and sharp angles by photolithography or any other process, at least the corners are rounded. At least in the corners, the straight line deviates from the ideal shape and shows curvature. Such curvature can constitute up to 20% of the line length when the size of the output element is extremely small, depending on the size of the output element. Such defects due to the manufacturing process are understood as tolerances included in the term "straight line", but even when the corners are rounded, specifically, the line for defining the blaze angle includes at least one straight line segment. And the blaze angle is defined by the orientation of at least one of these straight line segments with respect to the plane of the main surface.

[0004] This type of output element has been known conventionally and is often realized as a recess on another flat surface. For example, US2018 / 0088270A1, particularly in FIG. 5A, shows a typical embodiment. However, in the application of current technologies, a light guide using the above or similar output elements does not emit light in a uniform manner even if the distribution of the output elements corrects for uniform illuminance. Light from the illumination source is typically coupled to the light guide in a lateral plane. Near such a lateral plane, when visually inspecting the light guide, hot spots (bright spots separated by small dark regions) are visible, and the hot spots are connected along the lateral plane or edge respectively. Also, in the case of multicolor illumination, the light guide exhibits a dispersion where bright stripes and dark stripes forming a rainbow pattern extend on a main plane parallel to the edge of the lateral plane and are alternately arranged in one direction along a main plane perpendicular to the edge. When such a light guide is used in a display, the visual impression of the observer is impaired. However, no measures for improving the visual impression by removing hot spots and dispersion artifacts have been disclosed in the prior art.

[0005] EP2474846A1 discloses a diffractive light output coupling unit for forming part of a directional light output coupling system including such a plurality of output coupling units. The diffractive light output coupling unit includes a carrier element that houses a diffractive surface relief pattern and transports light. This diffractive surface relief pattern includes a plurality of continuous diffractive surface relief forms defined on a predetermined surface of the carrier element. The diffractive surface relief pattern is configured to enhance the directivity of outputting collimated and coupled light by coupling the incident light through the interaction regarding at least two surface relief forms among the plurality of continuous diffractive surface relief forms, where some light rays of the diffracted incident light pass through at least the first surface relief form during the interaction. No measures for avoiding the artifacts are taken.

[0006] EP1016817A1 discloses a light guide tube that provides backlighting for a flat panel display by at least one light source and has a sponsor surface including a specific pattern. Such a pattern has diffraction characteristics that conduct light in the direction of the display and includes uniform and different regions having a specific distribution on the surface of the light guide tube. The local output coupling efficiency of the light guide tube depends on the characteristics of the pattern that depend on the distance from the light source and the wavelength. The possibility of artifacts such as the aforementioned hot spots and rainbow-like features has not been discussed.

[0007] US6,773,126B1 discloses an optical panel including a light source and a panel element operably connected to the light source. The panel element includes a substantially transparent light-transmitting material and operates as a waveguide panel, and the light beam received from the light source propagates by total internal reflection inside the waveguide panel. A diffraction output coupling system is disposed above the light surface of the panel element and operates to couple and output the light beam from inside the panel element. The diffraction output coupling system includes a plurality of local grating elements. The local grating elements have a plurality of forms and are optimized such that the diffraction efficiency varies depending on the position. The reduction or avoidance of the artifacts as described above and the possibility of the artifacts have not been discussed.

[0008] US9,261,639B1 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 transporting the light by total internal reflection. The first main surface of the light guide includes a concave region having a circular contour (e.g., a quarter-circle contour) for reflecting light from the light guide to the pixelated display panel. A first optical layer covering at least a part of the first surface of the light guide fills the concave region included in the first surface of the light guide. A second optical layer covering at least a part of the second surface of the light guide transmits the reflected light to the pixelated display panel. Incidentally, the artifacts as described above are not the subject of discussion.

[0009] Finally, WO2019 / 087118A1 discloses a light distribution structure such as a light guide and related components. The structure preferably includes an optical functional layer of at least one feature pattern constructed on a light transmissive carrier by a plurality of three-dimensional optical features that are variable according to at least one parameter among the cross-sectional profile, size, periodicity, orientation, and arrangement within the feature pattern. For example, the optical feature is embodied as an internal optical chamber capable of establishing a total reflection function in its horizontal and substantially vertical planes. The possibility of artifacts such as the above-mentioned hot spots and rainbow-like features is not discussed here either.

[0010] In the current technology, artifacts related to the output coupling structure (e.g., hot spots and rainbow-like features) have not been noticed (when observed), and no countermeasures applicable to reducing or avoiding such artifacts have been described.

[0011] Of course, it is also possible to couple a light guide to additional optical layers such as a diffusion layer or a prism sheet. However, such measures not only increase the thickness of the layer assembly incorporated in the display, but may also reduce the luminance and / or angular illuminance distribution. In particular, since the thickness of the layer assembly is becoming an increasingly important feature in current applications, using additional layers is a drawback. SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0012] Therefore, as described above, an object of the present invention is to improve the light guide so as to avoid or at least reduce artifacts such as hot spots and rainbow-like features without requiring additional optical layers, especially when using a light guide in a display screen. MEANS FOR SOLVING THE PROBLEM

[0013] This object is achieved by dividing the plurality of output elements into at least two output element groups. Each group being complementary to each of the other groups means that a randomly selected output element belongs to only one of the output element groups. As previously explained, the members of each output element group have a common characteristic blade angle and thus have a common characteristic output coupling characteristic. The common characteristic blade angle and the common characteristic output coupling characteristic are different from the characteristic output coupling characteristics and blade angles of the members of the other groups, i.e., each output element group has its own unique blade angle and resulting output coupling characteristic. Thereby, light is output-coupled with different angular distributions for different output element groups. Thus, each output element group plays the role of output-coupling light with a specific angular distribution (specifically, a first angular range). By at least partially mixing such different angular distributions of light, visual artifacts (specifically, rainbow-like features or hot spots) in the optical characteristics of the output coupling can be minimized or at least reduced compared to the prior art.

[0014] Groups containing different output elements may have the same size, and each group may contain the same number of output elements, but this is not a requirement, and the groups may contain different numbers of output elements. In fact, this number can vary very widely. To improve the result, it is sufficient to define only two output element groups, where one of the groups contains 99% of all the output elements (i.e., the plurality of output elements), and the other group contains only 1% of all the output elements. However, by allocating more of the output elements to the other group, the result of avoiding visual artifacts can be further improved. This starts with groups having approximately the same number of elements when the relationship of the group sizes is predefined in an optimization program.

[0015] The output coupling angular distribution consists of at least a first angular range defined by projection onto the plane of the longitudinal section, but preferably consists of a second angular range defined by projection onto the main plane. Both of the two angular ranges are characteristic output coupling characteristics. However, as will be further explained below, the second angular range does not depend on the blaze angle. The size of the first angular range mainly depends on the angular spectrum of the incident light. All output element groups are different at least in the first angular range, but preferably, the output element groups are different in both the first angular range and the second angular range, and artifacts can be better reduced than when they are different only in either the first angular range or the second angular range.

[0016] As described above, the longitudinal section is formed into a substantially polygon having at least three corners and the same number of connecting lines. In one preferred embodiment, the substantially polygon has exactly three corners connected by three connecting lines. Also, the term "formed into a substantially polygon" means an ideal shape including tolerances due to manufacturing defects. On a microscale, a surface roughness between 5 nm and 10 nm is possible. The first connecting line is the baseline of a straight segment located in a plane parallel to one of the main surfaces. The second connecting line is arranged at an angle between 75° and 90°, preferably between 85° and 89°, particularly 88° with respect to the first connecting line. Finally, the third connecting line of the selected line connects the distal ends of the first connecting line and the second connecting line. The third connecting line, together with the first connecting line, surrounds a blaze angle to define characteristic output coupling characteristics. Each of the first connecting line and the third connecting line and preferably further the second connecting line includes at least one straight segment having a length of at least 60% of the total length of the line, and the straight segment extends to both sides of the center of each line. However, in practice, for manufacturing reasons, the second connecting line may be formed as an "S" curb having a very slight curvature along most of the line, making it difficult to define a straight segment. In this case, in order to appropriately define the angle formed by the second connecting line and particularly the first connecting line, it is approximated by an approximate straight line corresponding to the tangent line cut at the center of the second connecting line. A light guide having an output element of such a shape is easier to manufacture than a light guide having a curved connecting line. However, considering manufacturing defects as described above, in an optimization program, the connecting line can be approximated by an exponential function or a polynomial function of up to fifth order. In any case, there is and may be a deviation from a straight line due to manufacturing defects within a predetermined tolerance range.

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

[0018] The partial rotation angle substantially defines the size of the second angle range, and the blaze angle substantially determines a first angle range that further depends on the angle of light incident on the plane defined by the third connection line. Specifically, the blaze angle is different for different output element groups. For example, in the first group, the blaze angle is 53°, while in the second group, the blaze angle may be 57°. Both groups may include approximately the same number of output elements. In another embodiment, the first group includes output elements having a standard blaze angle of 55°, which is particularly useful for an optimal angular distribution in light guides used in the automotive industry. Other groups include output elements having blaze angles that are preferably symmetrically distributed about the standard blaze angle of 55° (e.g., 54° and 56°, or 53° and 57° in the second and third groups, respectively). More output element groups may be defined, for example, as a total of five groups having deviations of -3°, -2°, 0°, 2°, and 3° about a standard blaze angle (not necessarily 55°). Each group may include approximately 20% of all the output elements.

[0019] Output elements may be provided within at least one group of output elements, and thus, for at least one output element of at least said output element group, the blaze angle varies continuously or discretely between two end positions of the partial rotation. This particular example is useful from a manufacturer's perspective because, in addition to contributing to a better reduction of artifacts, it allows the use of only one group of output elements that are easier to manufacture by using output elements with varying blaze angles. This is a special situation of the present invention where only two output element groups are realized, but the second group is an empty group and thus has no members. In practice, only one group exists. However, this particular example can effectively reduce artifacts even when applied to one or more output element groups.

[0020] The light guide is usually made of a transparent thermoplastic material, a thermoelastic plastic material, or glass. The maximum dimension of the output element in each spatial direction is usually 100 μm, preferably between 1 μm and 30 μm. Thereby, it is possible to avoid the output element itself being visually recognized by the observer when the light guide is in use. Also, when the size of each output element is smaller than the sub-pixel of the LC panel, a plurality of output elements can cover the sub-pixel. This is advantageous for reducing or avoiding so-called color flicker.

[0021] The output elements of at least one output element group protrude from at least one of the main surfaces or extend to at least one of the main surfaces. Alternatively or in combination, the output elements may be formed as microprisms. Also, the output elements of at least one output element group may be formed as cavities inside the light guide. In this case, the cavity is evacuated or filled with a material having a refractive index and / or haze value that are different from the refractive index and / or haze value of the material of the light guide, respectively. In the case of the refractive index, it is preferable that the refractive index inside the cavity is lower than the refractive index outside the cavity in the light guide, and in the case of the haze value, it is preferable that the haze value inside the cavity is higher than the haze value outside the cavity in the light guide. Of course, each output element group can be realized in different forms. For example, the first output element group extends to one of the main surfaces, the second group is formed as a microprism protruding from one of the main surfaces, and the third group includes output elements formed as cavities. When the light guide is one element in a stack of other optical layers, it is naturally advantageous to keep the height of the light guide in the stack as small as possible, and since the output elements can be applied after the light guide is manufactured, it is preferable to extend output elements that are easier to manufacture than the cavities in the light guide to the main surface.

[0022] The distribution pattern of the output elements within at least one main surface and / or the volume of the light guide is preferably predetermined such that light is coupled and output with an illuminance uniformity of at least 60%, preferably 70% or more, on at least one of the two main surfaces by the output elements. In the case of such white uniformity, artifacts will not be seen interferingly by a user equipped with a device having such a light guide. The distribution pattern can be predetermined by a commercially available optical simulation program (for example, the optical modeling tool "Backlight Pattern Optimization" module of Synopsys), and the optical simulation program can include conditions for the input of the optimization program. The illuminance uniformity is measured by a nine-point program using a camera positioned vertically above the main surface at a distance of 90 cm. For reference, refer to Chapter 8 of the Measurement Standards for Information Display Devices issued by the International Display Measurement Committee (Version 1.03 as of June 1, 2021).

[0023] For example, near the lateral surface optically coupled to the light guide (if two output element groups are used), the two groups of elements are provided equally in a relationship of about 50% and 50%, and as the distance from the lateral surface increases, one of the groups of elements becomes dominant over the other group and can be selected such that it grows continuously up to a relationship of 100% and 0%. Thereby, the overall illuminance of a predetermined viewing angle region of a display incorporated in such a light guide increases. By selecting the distribution pattern in this way, it is also conceivable that the angular spectrum of the light coupled to the light guide changes between the lateral surface to which the input light is coupled and the lateral surface facing the lateral surface.

[0024] Also, each of the output elements contributes more or less to the overall haze of the light guide. In one preferred embodiment, (i) the distribution pattern of the output elements within at least one main surface and / or the volume of the light guide, (ii) the number of output elements, and (iii) their size are predetermined such that an average haze of 30% or less is generated at at least 50% of one of the main surfaces. Here, the haze value is measured according to Program A of ASTM D1003-13.

[0025] Furthermore, the present invention further relates to a display screen comprising the above-described light guide. The display screen includes, in addition to the light guide, one or more light sources that emit light coupled to the light guide on at least one of the lateral surfaces. The display screen further includes a transmissive display panel located in front of the light guide as viewed from the observer's viewpoint. The transmissive display panel and the light guide are usually separated only by an air layer or optically bonded to each other, and in many cases, no other optical layer is disposed between the display panel and the light guide.

[0026] The light guide includes output elements, and usually, the transmissive display panel includes pixels. In this case, by making the spatial extension of the output elements smaller than the spatial extension of the pixels in each dimension in the Cartesian space, more uniformity can be improved, and contrast and color flicker can be reduced or prevented. When the transmissive display panel includes pixels composed of sub-pixels, it is preferable that the spatial extension of the output elements is smaller than the spatial extension of the sub-pixels in each dimension in the Cartesian space.

[0027] It should be understood that the foregoing features and the features described below are applicable not only to the described combinations but also to different combinations or separate combinations without departing from the framework of the present invention described herein.

Brief Description of the Drawings

[0028] Hereinafter, the present invention will be described in more detail with reference to the drawings, which also show the features necessary for the present invention and other features. The specific examples shown in the drawings are for explaining the present invention, and the present invention is not limited to the said drawings. For example, the description of a specific example having a plurality of elements or assemblies does not mean that all of the said elements or assemblies are essential for implementing the present invention. In fact, different specific examples may include alternative elements or assemblies, fewer elements or assemblies, or additional elements or assemblies. The elements or assemblies of different specific examples can be combined with each other unless the contrary is explicitly stated. The modifications and variations described for one of the above specific examples are also applicable to other specific examples. To avoid redundant explanations, the same reference numerals are assigned to the same elements or elements related to each other in different drawings, and redundant explanations are omitted.

[0029]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0030] FIG. 1 shows a light guide 1 having two main surfaces, namely a bottom main surface and a top main surface. Here, the bottom main surface 2 is shown, but in other embodiments, it may be the top main surface. Each main surface has at least one edge surrounding the main surface. In the embodiment of FIG. 1, the bottom main surface 2 and the top main surface have four edges 3 surrounding the main surface. The shape of the edge 3 surrounding the light guide 1 mainly depends on the purpose of use of the light guide 1. For example, in an ATM or a notebook computer, the shape often appears to be similar to the shape shown in FIG. 1. However, in an automobile, the shape must more or less conform to a design having rounded edges or edges of different shapes. In the illustrated embodiment, the light guide 1 is plate-shaped, the two main surfaces are flat and parallel to each other. In other specific examples, the main surfaces may have a curvature and / or form a wedge shape. At the edge 3, the main surfaces are connected by lateral surfaces arranged perpendicular to the plane of the paper in the embodiment shown in FIG. 1. The light guide 1 has a transparency of at least 70% with respect to light passing through the light guide through the two main surfaces.

[0031] The light guide 1 is provided with a plurality of three-dimensional light output elements 4, 5 on at least one of the main surfaces. In the embodiment of FIG. 1, the light output elements 4, 5 are located only on the bottom main surface 2. Other specific examples of the light guide additionally or alternatively include light output elements 4, 5 on the top main surface. Additionally or alternatively, the plurality of light output elements 4, 5 may be provided within a volume surrounded by the main surface and the lateral surface. For most of the output elements 4, 5, any output element 4, 5 is at least 1 μm away from any other output element 4, 5. The output elements 4, 5 have a longitudinal section in a plane perpendicular to the bottom main surface 2. The longitudinal section is formed in a substantially polygon having three corners and three connecting lines connecting the corners. One of the three connecting lines is a selected line, and if the selected line is not straight over its entire length, it includes at least one straight segment. As will be further described below, the orientation of the straight segment with respect to the bottom main surface 2 defines a blaze angle so that total reflection is interfered by refraction and / or reflection to define a first output coupling angle range, thereby defining characteristic output coupling characteristics.

[0032] The plurality of output elements 4, 5 are divided into several groups of output elements 4, 5. Each group is complementary to each of the other groups, and the members of each group have a common characteristic blaze angle, and thus have at least one common characteristic output coupling characteristic. The common characteristic blaze angle and the at least one common characteristic output coupling characteristic are different from the characteristic output coupling characteristics and blaze angles of the members of the other groups. As a result, the light is output-coupled at different angular distributions depending on the group to which each output element belongs. In the specific example of FIG. 1, there are two output element groups: a first group having the first output element 4 and a second group having the second output element 5. However, two or more output element groups may be realized in the light guide 1.

[0033] The light output elements 4, 5 (or simply the output elements 4, 5) are distributed according to a distribution pattern predetermined by, for example, a commercially available optical design program as described above, so as to be coupled to the light guide 1 on at least one of the lateral surfaces, and with respect to the light that propagates in the light guide 1 by total reflection before being incident on the output elements 4, 5, one of the two main surfaces preferentially couples and outputs a larger amount of light than the other of the two main surfaces. For total reflection, the light must be coupled only within a limited angular range in the light guide.

[0034] In the specific example shown in FIG. 1 where the light output elements 4 and 5 are located on the bottom main surface 2, it is preferable that the top main surface couples and outputs light with a higher light quantity than the bottom main surface 2. This situation is shown in detail in FIG. 2, which shows a cross-section passing through the light guide 1 similar to FIG. 1. However, in FIG. 2, for the sake of simply deepening the understanding, the output elements 4 and 5 are arranged at equal intervals from each other, but in reality, this is not the case. In relation to FIG. 1, the cross-section is perpendicular to the paper surface and extends from the bottom to the top, corresponding to from left to right in FIG. 2. On the left side of FIG. 2, a light source 6 that emits light along the light beam 7 is arranged, and the light beam enters the light guide 1 through the lateral surface 8. In relation to FIG. 1, this lateral surface 8 is located at the lower edge 3 of the bottom main surface 2. Note that the light source 6 does not emit a single light beam, but the light source emits light along the main part of the lateral surface. This is encoded in FIG. 2 by a plurality of light beams 7 (solid line light beam, dashed line light beam, and dash-dotted line light beam) corresponding to different depths perpendicular to the paper surface. Further, since the angular spectrum is limited to an angle that enables total internal reflection of light on the plane main surface, the light beam 7 is emitted within a small angular range that allows the light to propagate through the light guide 1 without being coupled and output when the output elements 4 and 5 do not exist. A reflection coating for minimizing light loss may usually be provided on the lateral surface facing the light source 6.

[0035] However, due to the presence of the first output element 4 and the second output element 5, light is coupled out from the light guide 1. The solid light beam 7 enters the light guide 1 in the lateral plane 8. This solid light beam is totally reflected by the leftmost output element 4 and is depicted by the solid line. By being reflected at an angle, the light passes through the top main surface of the light guide 1 and leaves the light guide at a predetermined angle. This is similarly applicable to the dashed beam 7 reflected by another first output element 4, which is at a deeper position in the light guide 1 as seen from the plane of the paper. Finally, the beam 7 indicated by the dash-dotted line is reflected by the second output element 5, which is located between the other two light output elements 4 in the light guide 1 with respect to the depth dimension of the light guide 1. However, the second output element 5 is slightly different in shape from the first output element 4. Therefore, compared with the light reflected by the first output element 4, the reflection angle is different, and the dash-dotted light beam 7 leaves the light guide at a different angle. This is advantageous for reducing artifacts such as hot spots and rainbow-like features together with the predetermined distribution of the output elements.

[0036] The light output elements 4 and 5 usually have a maximum dimension of 100 μm in each spatial direction, but preferably, the maximum dimension is 1 μm to 30 μm. In the specific examples shown in FIGS. 1 and 2, since the light output element is formed as a recess, it extends to the bottom main surface 2. However, the light output element may be formed on two main surfaces or may be formed as a cavity inside the light guide. The light output element may be formed as a protrusion and / or may be shaped as a micro prism. If the output element is formed as a cavity, such a cavity may be evacuated or filled with a material having a refractive index and / or haze value different from those of the material of the light guide 1. The light guide 1 may be formed of a thermoplastic material (e.g., PMMA, polycarbonate, PMMI) or may be formed of glass. It is also possible that at least two output element groups include different types of output elements. For example, the first output element group includes output elements formed as protrusions from at least one of the main surfaces, the second group of output elements is formed as cavities inside the light guide 1, and the third group of output elements may be formed as recesses on at least one of the two main surfaces.

[0037] In the specific example shown in FIG. 1, on the bottom main surface 2, the distribution pattern of the output elements 4 and 5 in at least one of the two main surfaces and / or within the volume of the light guide 1 is preferably predetermined such that light is coupled and output with an illuminance uniformity of at least 60% to at least one of the two main surfaces (here, the top main surface) by the output elements 4 and 5.

[0038] Preferably, each of the output elements 4 and 5 contributes to the overall haze of the light guide 1, and the distribution pattern, number, and size of the output elements 4 and 5 on the bottom main surface 2 are predetermined so that an average haze of 30% or less is generated at least 50% of the top main surface (the surface facing the surface where the output elements 4 and 5 are located). In this way, each of the output elements contributes to the overall haze of the light guide 1. For example, the haze can be measured according to ASTM D1003-13.

[0039] Hereinafter, the output elements 4 and 5 will be described in more detail. FIG. 3 shows an output element 4 or 5 having an ideal shape. FIG. 3A) is a perspective view of the output element, FIG. 3B) is a projection view from the top or bottom, and FIG. 3C) is a longitudinal sectional view of the coupling elements 4 and 5 along the dashed-dotted line shown in FIG. 3B).

[0040] The longitudinal section always means a section passing through the output element along a plane as shown in FIG. 3B) (that is, along the direction that coincides with the shortest distance between the entry point and the exit point, along the dashed-dotted line in FIG. 3B)) so that the area of the section is minimized. Since the curve of the output element projected in FIG. 3B) has the shape of an arc having a common center point, the sectional plane cuts two arcs perpendicular to its tangent.

[0041] However, due to the constraints of the manufacturing process (for example, forming an optical tool using photolithography technology and manufacturing a light guide using nanoimprinting and / or injection molding processes), it is very difficult to fabricate an ideal structure as shown in FIGS. 3A) to 3C). Therefore, the actual structure of the output elements 4 and 5 deviates more or less from this ideal shape and tends to look like the shapes shown in FIGS. 4A) to 4C). Specifically, as can be seen in the longitudinal section shown in FIG. 4C), the corners are rounded.

[0042] Generally, each of the output elements 4, 5 has a longitudinal section in a plane perpendicular to at least one of the main surfaces, for example, as shown in FIG. 3C) or FIG. 4C), and the longitudinal section is formed in a substantially polygonal shape having at least three corners and at least three connecting lines connecting the corners, and the connecting lines are curves or straight lines. The longitudinal section of FIG. 3C) has three corners connected by straight lines. On the other hand, the more actual longitudinal section shown in FIG. 4C) has rounded corners. The basic polygon can be defined in two ways equivalent to the optical effect, and this effect does not depend on the actual shape of the corners, as will be further explained below. The first possibility is to further extend the straight lines or straight line segments until they intersect each other to form a shape as shown in FIG. 3C). The second possibility is to approximate the rounded corners by a number of short straight lines. At the limit of infinitely short lines, the rounded corners can be approximated by a function (e.g., by a polynomial function). In the longitudinal section shown in FIG. 4C), the output elements 4, 5 are formed as recesses in the light guide 1, where the plane of the bottom main surface 2 is perpendicular to the paper surface and includes the horizontal baseline 9 (with respect to the paper surface) of the output elements 4, 5. The output elements protruding from the main surface have the same shape. When the output elements are within the volume of the light guide 1, two lower corners having a convex shape when viewed from the inside of the output elements in FIG. 4C) have a concave shape conversely.

[0043] The output elements 4, 5 in FIGS. 3 and 4 have a longitudinal section, and this longitudinal section is merely approximately formed in a polygonal shape having three corners in FIG. 4. The corners are connected by connecting lines. The first connecting line is the baseline 9 located in a plane parallel to one of the main surfaces (here, the bottom main surface 2). When the output element is formed as a recess, the first connecting line is a straight line, and in other specific examples, the first connecting line includes at least a straight line segment.

[0044] The second connection line 12 is arranged at an angle between 75° and 90° with respect to the baseline 9. In the embodiments shown in FIGS. 3 and 4, this angle is 90°. However, in practice, it has been found that it is preferable to select an angle less than 90°, specifically in the range of 85° to 89° (for example, 88°). In any case, the angle may be selected so that the surface defined by the rotation of the second connection line 12 is not irradiated with light. Realistically, the second connection line may have a shape of "S" with a slight curvature and a deviation from a linear shape regarded as surface roughness in the range of 5 nm to 10 nm. Then, as described above, the angle is determined.

[0045] The third connection line 13 connects the distal ends of the baseline 9 and the second connection line 12. The third connection line 13 is a selected line, and together with the baseline 9, it defines characteristic output coupling characteristics by surrounding the blaze angle 11. When the third connection line 13 is curved, the straight segment 10 included in the third connection line preferably has a length of at least 60% of the total length of the third connection line 13. A length less than 60% is also effective, but the efficiency decreases slightly. Output coupling is realized when, as in the case of the output elements 4 and 5 formed as recesses in the light guide 1 as shown in FIGS. 1 and 2, the light is reflected by the straight line 13 or the straight segment 10 respectively and then passes through the main surface on the opposite side and leaves the light guide 1.

[0046] The orientation of the straight segment 10 or at least one main surface of the straight line (here the bottom main surface 2) with respect to the plane defines the blaze angle 11 so that total reflection is interfered by the reflection and / or refraction of the light irradiated on each surface including the straight segment 10, and the first output coupling angle range is defined as characteristic output coupling characteristics, thereby defining characteristic output coupling characteristics. In other words, the output coupling angle range is directly related to and depends on the respective orientations of the straight line or the straight segment 10 with respect to the plane of the main surface.

[0047] In this specific example, the three-dimensional shape of each of the output elements 4 and 5 is defined in a plane perpendicular to the longitudinal section by a partial rotation of the longitudinal section about a central axis parallel to the longitudinal section and outside the longitudinal section. Another possibility is to define the three-dimensional shape by a translation of the longitudinal section. The rotation of the third connection line 13 defines the plane where the light beam 7 in FIG. 2 is reflected here, or the plane refracted in other specific examples. The partial rotation angle is preferably within a range between 5° and 25° including such an angle, different from 0°. As shown in FIGS. 3A) and 4A), perspective views of the output elements 4 and 5 are shown, and FIG. 5 shows two embodiments of output elements having different partial angles. FIG. 5A) is a bottom view of the first output element 4 along the observation direction entering from the bottom main surface 2 into the light guide 1. FIG. 5B) is a bottom view of the second output element 5. The central axis is marked by a cross and is oriented perpendicular to the plane of the paper. The partial rotation angle of the first output element 4 is 25°, and is larger than the partial rotation angle of the second output element 5, and the partial rotation angle of the second output element 5 is 15°. Also, the arc of the reflecting surface of the second output element 5 has a stronger curvature than the arc of the first output element 4 because the radius of the second output element 5 (i.e., the distance from the central axis) is shorter.

[0048] In the embodiments shown in FIGS. 3 and 4, the shape of the longitudinal section is always the same regardless of the position of the section. Therefore, the blaze angle 11 is constant over the entire output element. However, it is also possible to combine a partial rotation with a discrete or continuous change that varies according to the rotation angle of the blaze angle 11, which means that the shape of the longitudinal section depends on the position with respect to the rotation. The blaze angle 11 may vary continuously or discretely between the two end positions of the partial rotation (for example, between 53° and 57°). In one preferred specific example, the blaze angle varies for at least one group of output elements. Thereby, it is possible to further reduce artifacts, and basically, only one group of output elements that are easier to fabricate can be used.

[0049] As described above, the light guide includes a plurality of output elements divided into at least two complementary output element groups. In a specific example related to the drawings, the plurality of output elements are divided into two groups, and the members of each group have a common characteristic blaze angle 11, and thus have a common characteristic output coupling characteristic. The common characteristic blaze angle and the common characteristic output coupling characteristic are different from the characteristic output coupling characteristics and blaze angles of the members of the other group. Thereby, light is output-coupled at different angular distributions for different output element groups. In the above-described specific example, the output coupling angular distribution includes a first angular range and a second angular range. The latter is defined by projection onto the main surface. This is shown for the first output element 4 in FIG. 5A) and for the second output element 5 in FIG. 5B). The second angular range is defined by a partial rotation angle corresponding to the dimensions of each segment for a 360° full rotation that generates a donut shape. The partial rotation angle is directly related to the second angular range and defines a second characteristic output coupling characteristic that is not related to the blaze angle 11. The blaze angle 11 needs to be different for different groups of the output elements 4, 5, but the partial rotation angle, and thus the second characteristic output coupling characteristic, may be the same for all groups.

[0050] The output coupling angular distribution further includes a first angular range defined by the projection onto the plane of the longitudinal section. This is shown for the first output element 4 in FIG. 6A) and for the second output element 5 in FIG. 6B). As explained with respect to FIG. 2, light enters the light guide 1 at different angles within a limited angular spectrum. The light beams within this angular spectrum are finally reflected in the plane defined by the rotation of the third connection line 13, as explained with respect to FIGS. 3 and 4. Each first angular range is shown as a shaded cone and is different when measured with respect to the baseline 9. The light irradiated onto the plane defined by the rotation of the third connection line 13 along the horizontal direction (with respect to the plane of the paper) is reflected in the direction bisecting the shaded cone. As can be seen from FIGS. 6A) and 6B), the first angular range is directly related to the blaze angle 11, which defines the inclination of the third connection line 13 or its straight segment 10, and thus defines the inclination of the plane of the reflected light beam. The first angular range is the same for members of the same output element group, but defines different first characteristic output coupling characteristics for members of different output element groups.

[0051] FIG. 7 shows a display screen including the above-described light guide 1. The display screen further includes one or more light sources 6 that emit light coupled to the light guide 1 at least on one of the lateral surfaces 8 (here, the left lateral surface 8). The transmissive display panel 14 is located in front of the light guide 1 as seen by the observer. In the specific example shown in FIG. 7, the transmissive display panel 14 and the light guide 1 are separated only by the 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 via a highly transparent adhesive having a refractive index suitable for the refractive index of the light guide 1 to minimize reflection. Thus, in order to enable total internal reflection within the light guide 1, the refractive index of the bonding material must be lower than the refractive index of the material constituting the light guide 1. Avoiding the use of additional optical layers is important in bright environments to minimize potential losses in the brightness of the display.

[0052] When the light guide 1 is used together with a transmissive display panel 14 including pixels or pixels each composed of sub-pixels, it is preferable that the spatial extension of the output elements 4 and 5 is smaller than the spatial extension of the pixels or sub-pixels in each dimension (i.e., each of the three spatial directions) in the Cartesian space.

[0053] When the above-described light guide 1 is used together with the transmissive display panel 14, artifacts such as hot spots and rainbow-like features are significantly reduced compared to a transmissive display panel having a conventionally known light guide, thus improving the observer's viewing experience.

Explanation of Reference Numerals

[0054] 1: Light guide 2: Bottom main surface 3: Edge 4: Light output element / Output element / First output element / Coupling element 5: Light output element / Output element / Second output element / Coupling element 6: Light source 7: Light beam 8: Lateral plane 9: Horizontal baseline / Baseline / Connection line 10: Straight line segment 11: Blaze angle / Common characteristic blaze angle / Characteristic blaze angle 12: Second connection line / Connection line 13: Third connection line / Straight line / Connection line 14: Transmissive display panel 15: Air layer

Claims

Claim 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 a lateral surface at the edge (3), the light guide (1) comprising a plurality of three-dimensional light output elements (4, 5) within a volume surrounded by the two main surfaces and the lateral surface (8), the light output elements (4, 5) being distributed according to a predetermined distribution pattern, the light guide (1) having a transparency of at least 70% with respect to light passing through the light guide through the two main surfaces, the distribution pattern being predetermined, and light coupled to the light guide (1) on at least one of the lateral surfaces (8) being designed to propagate within the light guide (1) by total reflection before being incident on the light output elements (4, 5), the distribution pattern preferentially coupling and outputting a higher amount of light from one of the two main surfaces than from the other of the two main surfaces, the light output elements (4, 5) having a longitudinal section in a plane perpendicular to at least one of the main surfaces, the longitudinal section being formed in a substantially polygonal shape having at least three corners and at least three connecting lines (9, 12, 13) connecting the corners, one of the at least three connecting lines (9, 12, 13) including a selected line of at least one straight segment (10), the orientation of the straight segment (10) with respect to the plane of at least one of the main surfaces defining a blaze angle (11) such that total reflection is interfered with by refraction and / or reflection and a first output coupling angle range is defined, thereby defining characteristic output coupling characteristics, wherein for most of the light output elements (4, 5), any light output element is at least 1 μm away from any two arbitrarily close light output elements, The plurality of light output elements (4, 5) are divided into several groups of light output 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 thus having a common characteristic output coupling characteristic, where the common characteristic blaze angle (11) and the common characteristic output coupling characteristic are different from the characteristic blaze angle (11) and output coupling characteristic of the members of the other group, whereby light is output-coupled at different angular distributions for different groups of light output elements (4, 5), a light guide (1).

2. The output coupling angular distribution consists of a first angular range defined by the projection of the longitudinal section onto the plane and a second angular range defined by the projection onto the main plane, the light guide (1) according to claim 1.

3. The longitudinal section 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 a straight segment located in a plane parallel to one of the main planes, the second connecting line (12) being arranged at an angle between 85° and 90° with respect to the first connecting line, the third connecting line (13) connecting the distal ends of the first connecting line and the second connecting line (12), the third connecting line (13) being the selected line and, together with the first connecting line, defining a characteristic output coupling characteristic by surrounding the blaze angle (11), the light guide (1) according to claim 1 or 2.

4. The three-dimensional shape of each of the light output elements (4, 5) is, in a plane perpendicular to the longitudinal section, parallel to the longitudinal section and centered on a central axis outside the longitudinal section, the partial rotation angle being different from 0° and being defined by the partial rotation angle of the longitudinal section, the light guide (1) according to claim 3.

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

6. The light output elements (4, 5) have a maximum dimension of 100 μm in each spatial direction, the light guide (1) according to any one of claims 1 to 5.

7. The distribution pattern of the at least one main surface and / or the light output elements (4, 5) within the volume of the light guide (1) is predetermined such that light is coupled and output with an illuminance uniformity of at least 60% on at least one of the two main surfaces by the light output elements (4, 5), and the illuminance uniformity is measured by a 9-point program. The light guide (1) according to any one of claims 1 to 6.

8. Each of the light output elements (4, 5) contributes to the overall haze of the light guide (1), and (i) the distribution pattern of the light output elements (4, 5) on the at least one main surface and / or within the volume of the light guide (1), (ii) the number of light output elements (4, 5), and (iii) its size are predetermined, whereby an average haze of 30% or less is generated on at least 50% of one of the main surfaces, and the haze is measured according to ASTM D1003-13. The light guide (1) according to any one of claims 1 to 7.

9. The light output elements (4, 5) of at least one group of light output elements (4, 5) protrude from or extend into at least one of the main surfaces, and / or are shaped as microprisms. The light guide (1) according to any one of claims 1 to 8.

10. The light output elements (4, 5) of at least one group of light output elements (4, 5) are formed as cavities inside the light guide, and the cavities are evacuated or filled with a material having a refractive index and / or a haze value different from those of the material of the light guide (1). The light guide (1) according to any one of claims 1 to 9.

11. The light guide (1) according to any one of claims 1 to 10, one or more light sources (6) that emit light coupled to the light guide (1) on at least one of the at least lateral surfaces (8), a transmissive display panel (14) located in front of the light guide (1) as viewed from the observer's viewpoint, comprising a display screen.

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

13. The transmissive display panel (14) includes pixels composed of sub-pixels, and the light guide (1) includes light output elements (4, 5), and a spatial extension of the light output elements (4, 5) is smaller than a spatial extension of the sub-pixels in each dimension in a Cartesian space. The display screen according to claim 12.

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 only by an air layer (15) or optically bonded.

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