Light guide for a backlight, a backlight and a display device

Abstract

The present invention relates to a light guide (3) for a backlighting unit. The invention further relates to a backlighting unit comprising such a light guide (3) and to a display device comprising such a backlighting unit. The light guide (3) has at least one light coupling section (30), wherein the at least one light coupling section (30) comprises an arrangement of total internal reflection collimators (300); and a light guide section (32), wherein the light guide section (32) has a reflective inclined end surface (326), and wherein the light guide section (32) has a top surface (320) and a bottom surface (321), wherein the light guide section (32) is configured to guide the light (L3) coming from the light coupling section (3) within the light guide section (32) to the inclined end surface (326), and the light (L) reflected from the inclined end surface (326)g ) through the top (320).

Description

[0001] The present invention relates to a light guide for a backlighting unit. The invention further relates to a backlighting unit comprising such a light guide and to a display device comprising such a backlighting unit.

[0002] Modern vehicles provide drivers and other occupants with increasingly comprehensive information that goes far beyond simply displaying the vehicle's status. Consequently, conventional instrument clusters are being increasingly replaced by freely programmable digital displays. These displays often utilize a transmissive display panel, such as a liquid crystal display, in combination with a backlight unit.

[0003] Modern backlighting units are mostly based on edge-illuminated optical fibers (EOFs), into which the light from multiple LEDs is coupled via a side surface of the EMF. The light propagates through the EMF by total internal reflection and is coupled out again by special coupling structures on the surface of the EMF or by a specific choice of EMF geometry, such as a conical shape. To modify and improve the efficiency, homogeneity, and angular emission properties of the coupled-out light, additional components such as diffuser films, prism films, polarizing films, or special coatings are often used.

[0004] US 11,048,037 B2 discloses a backlight and a multiview display that use a light guide with an angle-preserving scattering function and a conical collimator. The angle-preserving scattering function is configured to scatter a portion of the guided light as emitted light from the light guide. The conical collimator is configured to collimate the light supplied by a light source and to transmit the collimated light as guided light to the light guide.

[0005] US 2007 / 0081360 A1 discloses a display backlight assembly that provides improved optical coupling between a solid-state light source and an optical display light guide. The assembly includes an optical coupler for coupling the solid-state light source and the optical light guide of the display. Additionally, the optical coupler can include a light mixing element for improved mixing of the multicolored or monochromatic light generated by the solid-state light source.

[0006] US 2017 / 0285242 A1 discloses a liquid crystal display device comprising a light source that emits light of a predetermined color, a lens that focuses the light emitted by the light source and causes the light to exit, a bandpass filter that allows light in a specific wavelength band to pass through the light exiting the lens, and a light guide plate arranged on the back of a display panel. The light transmitted through the bandpass filter is incident on a side surface of the light guide plate.

[0007] US 2017 / 0192239 A1 describes an optical fiber with a fiber optic element that has an incidence section through which image light emitted by an image display element enters the fiber optic element; an exit section through which the image light leaves the fiber optic element and is emitted to the outside; a retroreflection section for reversing the direction of propagation of the image light passed through the fiber optic element; and an extraction section for directing the image light, reversed by the retroreflection section, to the exit section. The retroreflection section has multiple surfaces.

[0008] WO 2020 / 170707 A1 discloses an optical element comprising: a light guide part with a main surface, several side surfaces perpendicular to the main surface and a rear surface facing the main surface; and a diffraction grating part formed on the main surface; wherein the rear surface is inclined at an angle with respect to the main surface.

[0009] DE 102020214082 A1 discloses a lighting device and a display with such a lighting device. The lighting device has at least one light source and a homogenizer for light emitted by the at least one light source. The light emitted by the at least one light source is coupled into the homogenizer by at least one coupling element. The homogenized light is coupled into an optical fiber that has structures for the directed extraction of the light homogenized by the homogenizer.

[0010] The typical beam pattern of an edge-lit backlight system has a wide angular distribution. While this characteristic is advantageous for many applications where the display needs to be readable from a wide angle, in some applications the light emitted by a display should be limited to a narrow angular range. Head-up displays or switchable privacy screens, for example, require a very narrow and well-defined angular beam pattern. This narrow distribution cannot be achieved with current edge-lit light guides, also known as edge-light configurations. Alternatively, direct-illuminated systems can be used, which illuminate the display with a series of light sources and some collimation optics. This configuration makes it possible to achieve narrow light distributions.However, to achieve acceptable homogeneity, the space required for the lighting system is significantly larger compared to edge-lit systems.

[0011] It is an object of the present invention to provide a compact edge-illuminated backlight unit for a display device with a narrow angular light distribution, high efficiency and homogeneous illumination.

[0012] This problem is solved by an optical fiber according to claim 1, by a backlighting unit according to claim 12, and by a display device according to claim 13. The dependent claims include advantageous further developments and improvements of the present principles, as described below.

[0013] From a first perspective, a light guide for a backlighting unit exhibits the following characteristics: - at least one light coupling section, wherein the at least one light coupling section comprises an arrangement of total internal reflection collimators, and - a light guide section, wherein the light guide section has a reflective inclined end surface, and wherein the light guide section has a top and a bottom surface, wherein the light guide section is configured to guide the light coming from the light coupling section within the light guide section to the inclined end surface, and couples out the light reflected from the inclined end surface through the top surface.

[0014] To generate a narrow light distribution with an edge-illuminated optical fiber, it is necessary to precisely control the angular distribution of the light propagating within the fiber. This is achieved by collimating the light during coupling. According to the invention, an array of total internal reflection (TIR) ​​collimators is used. In the simplest case, several TIR collimators are arranged side by side in a line, i.e., in a one-dimensional configuration. However, a two-dimensional, planar arrangement is also within the scope of the invention. Total internal reflection collimators are particularly advantageous because they are able to collect the light emitted by LEDs with high efficiency and restrict the collected light to a small angular range.

[0015] According to the invention, the collimated light first passes completely through the light guide section before being reflected at the inclined end surface. Due to the long light path, sufficient mixing of the light from different light sources occurs. Upon reflection at the inclined end surface, the propagation angle within the light guide section is also changed such that the light, while still undergoing total internal reflection, strikes the top or bottom surface at a significantly steeper angle. According to the invention, the inclined end surface of the light guide section is designed to reflect light that has already passed through the light guide section and reached the end surface. The light reaching the end surface is reflected and travels back through the light guide section in a different direction, i.e., not parallel to the direction of incidence.The end surface is designed such that reflection causes a change in the propagation angle of the reflected light. Advantageously, the end surface is inclined relative to the direction of propagation of the light guided within the light-guiding section. In this way, light is only coupled out during the back-propagation. For this purpose, appropriately designed microstructures are provided, for example.

[0016] The top and bottom surfaces of the light guide section are advantageously parallel to each other. This ensures that the nearly parallel light rays are almost always totally reflected at the top or bottom surface when they first pass through the light guide section.

[0017] It is also advantageous that the top and bottom surfaces have a slight opening towards each other in the direction of the initial light propagation from the light source to the opposite inclined end surface. Total internal reflection at the top and bottom surfaces is also ensured here.

[0018] The array of total internal reflection collimators is connected to a light guide section. For efficient light extraction, the light guide section has a small thickness to enhance the interaction of the light with its surfaces. This aspect of the invention thus enables the achievement of narrow light distributions with very high efficiency and good light mixing. The light guide can be manufactured, for example, by injection molding or by combining a glass light guide section with a light coupling section. The light guide can also be made entirely of glass.

[0019] In an advantageous embodiment, the underside of the light guide section has output structures, wherein the output structures have areas that are inclined relative to the underside of the light guide section and are configured to direct a portion of the light guided within the light guide section to the top side of the light guide section. By appropriately selecting the geometry of the output structures in the light guide section, only a fraction of the broadened angular distribution within the light guide section is output. As a result, the resulting angular distribution of the light on a display panel illuminated by the light guide remains very narrow.

[0020] In an advantageous embodiment, the length and taper of the tapered light mixing section, as well as the inclination of the end surface, are designed such that, in conjunction with the output coupling structures, the light coupled out of the light guide exhibits a narrow angular distribution. By correctly designing the conical light mixing section, the inclination of the end surface, and the output coupling structures, the angular distribution of the light can be very precisely controlled.

[0021] In an advantageous embodiment, the density of the output structures along a propagation direction of the light guided within the optical fiber is configured such that the light coupled out of the optical fiber exhibits a substantially constant brightness distribution over the entire length of the optical fiber. By increasing the density of the output structures along the propagation direction in the optical fiber, a substantially constant brightness distribution can be achieved. The increased density of the output structures compensates for the reduction in the available amount of light along the propagation direction.

[0022] In an advantageous embodiment, the light guide further comprises a diffuser film arranged on or above the top surface of the light guide section. Such a diffuser film can be used, for example, to further improve homogeneity and modify the angular distribution of the light.

[0023] In an advantageous embodiment, the light guide further comprises a reflective coating arranged on the underside of the light guide section. This significantly reduces light loss through the underside, thereby increasing the efficiency of the system.

[0024] In an advantageous embodiment, the light guide further comprises a reflective polarizer arranged on or above the top surface of the light guide section. The embodiment without a conical light guide section, i.e., the embodiment in which the top and bottom surfaces of the light guide section are arranged parallel to each other, enables the implementation of so-called polarization recycling. The reflective polarizer on or above the light guide section reflects light with a polarization state that would otherwise be absorbed by the display panel or another component downstream of the light guide, which is illuminated by the light guide. With the aid of a retardation layer or birefringence, the polarization state of the reflected light can be converted to a usable polarization state via retroreflection on the underside of the light guide section.For this purpose, the optical fiber advantageously includes a delay layer positioned between the top surface of the fiber optic section and the reflecting polarizer. Alternatively, the fiber optic section can be made of a birefringent material. Both approaches increase the efficiency of the system.

[0025] In an advantageous embodiment, the output structures have areas that run parallel to the underside of the light guide section. In this way, the output structures maximize reflection and preserve the direction of the recycled light.

[0026] In an advantageous embodiment, light coupling sections and conical light mixing sections are arranged on two adjacent sides of the light guide section, which are usually arranged at right angles to each other. This solution has the advantage that light can be coupled into the light guide section from two different sides, which further improves the homogeneity of the light coupled out of the light guide section.

[0027] Advantageously, an optical fiber according to the invention is used in a backlighting unit for a display device. The backlighting unit further comprises at least one arrangement of light sources configured to emit light in the direction of the total internal reflection collimators of the optical fiber.

[0028] Advantageously, a backlighting unit according to the invention is used in a display device, e.g., a display device for automotive applications. For example, the display device can be used in a head-up display or configured to provide switchable privacy functionality. Of course, the use of the backlighting unit is not limited to these applications. The described solutions are suitable for all types of applications that require homogeneous planar illumination units with controllable angular beam characteristics.

[0029] In one embodiment, the display device further comprises a prism film configured to change the direction of the illumination light emanating from the backlight unit. This is particularly useful when the viewing direction is not perpendicular to a display panel of the display device, which may be the case if the display panel is tilted to avoid sunlight reflections. The prism film can be part of the backlight unit or a separate component of the display device.

[0030] Further features of the present invention will become apparent from the following description and the attached claims in conjunction with the illustrations. Fig. Figure 1 shows a perspective view of an optical fiber according to the invention; Fig. Figure 2 shows a side view of the light guide of Fig. 1; Fig. Figure 3 shows a front view of a light coupling section from the optical fiber of Fig. 1; Fig. Figure 4 illustrates the light paths and decoupling structures of the optical fibers. Fig. 1; Fig. 5 shows a front view of a backlighting unit according to a first embodiment, which includes a light guide according to the invention; Fig. 6 shows a front view of a backlighting unit according to a second embodiment, which incorporates a light guide according to the invention; Fig. Figure 7 shows a section through a display device including a backlight unit with a light guide according to the invention; Fig. Figure 8 shows a side view of the light guide; Fig. Figure 9 shows a total reflection collimator; and Fig. Figure 10 shows another design of a light guide. Detailed description

[0031] The present description illustrates the principles of this disclosure. A person skilled in the art is able to deduce various arrangements which, although not expressly described or shown here, embody the principles of the disclosure.

[0032] All examples and conditional formulations reproduced herein are intended for clarification, to help the reader understand the principles of revelation and the concepts the inventor contributed to the advancement of technology, and are to be interpreted as not being limited to the specifically cited examples and conditions.

[0033] Furthermore, all statements contained herein that list principles, aspects, and embodiments of the disclosure, as well as specific examples thereof, are intended to include both structural and functional equivalents thereof. Moreover, it is intended that such equivalents include both currently known equivalents and those developed in the future, i.e., all developed elements that perform the same function regardless of their structure.

[0034] For example, experts will understand that the diagrams presented herein represent conceptual views that embody the principles of revelation.

[0035] Fig. Figure 1 shows a perspective view of an optical fiber 3 according to the invention. A side view of the optical fiber 3 is shown in Fig. Figure 2 shows the optical fiber 3 pointing to a light coupling section 30, a conical light mixing section 31, and a light guiding section 32. The light coupling section 30 has a first thickness d lis and comprises an arrangement of total reflection collimators 300. A front view of the light coupling section 30 and the arrangement of the total reflection collimators 300 is shown in Fig. Figure 3. The light guide section 32 has a length l. lgs and a second thickness d lgs , which is smaller than the first thickness d lis The conical light mixing section 31 has a length l lmsand connects the light coupling section 30 and the light guide section 32. The light guide section 32 has an upper surface, the top 320, and a lower surface, the bottom 321, and is configured to couple out light guided within the light guide section 32 through the upper surface 320. The light guide section 32 has a side surface 328. An end surface 326 of the light guide section 32 is advantageously designed to reflect light guided within the light guide section 32 and reaching the end surface 326. The end surface 326 is inclined so that the light is not reflected back onto itself. While in Fig. 1 and Fig. 2 If only one light coupling section 30 and one conical light mixing section 31 are present, light coupling sections 30 and conical light mixing sections 31 can also be arranged on the side surface 328 of the light guide section 32.

[0036] Fig. Figure 4 shows light paths and coupling structures 3210 of the optical fiber 3 of Fig. 1. The light L g , which is guided within the optical fiber section 32 of the optical fiber 3, runs, during its first passage through the optical fiber 3, from left to right in the illustration, essentially parallel along a propagation direction D P The output structures 3210 are arranged in a base surface 321 of the light guide section 32 of the optical fiber 3. During the first passage through the optical fiber 3, the essentially parallel light interacts little or not at all with the output structures 3210. In the exemplary embodiment, a reflective coating 323 is arranged on the underside 321 to reduce light losses through the underside 321. The output structures 3210 have areas 3211 that are inclined relative to the underside 321. The inclined areas 3211 are designed such that they reflect light L from the inclined end surface 326.g , which corresponds to the direction of propagation D p The light is guided at an angle within the light guide section 32, directed to the top 320 of the light guide section 32, where it at least partially leaves the light guide section 32 and thus emits coupled light L out educates.

[0037] The output structures 3210 also have areas 3212 that run parallel to the top surface 320. The light guide 3 is designed to implement so-called polarization recycling. A reflective polarizer 324 above the light guide section 32 reflects light L r with a polarization state that would otherwise be absorbed by a display field illuminated by the light guide 3. A delay layer 325 alters the polarization state of the reflected light L r During retroreflection at the underside 321, it is converted into the usable polarization state. The resulting recycled light Lrec is now able to pass through the reflective polarizer 324. The retardation layer 325 is, for example, designed as a retardation foil, a retardation film, or a retardation coating.

[0038] The length and taper of the conical light mixing section 31 of the optical fiber 3, as well as the inclination angle of the inclined end surface 326, are designed such that, in conjunction with the output coupling structures 3210, the light coupled out of the optical fiber section 32 exhibits a narrow angular distribution. A density of the output coupling structures 3210 along the propagation direction D p is advantageously designed such that the light L coupled out of the light guide section 32 out exhibits an essentially constant brightness distribution over the entire length of the light guide section 32.

[0039] Fig. Figure 5 shows a front view of a backlighting unit 2 according to a first embodiment, which uses a light guide 3 according to the invention. The light coupling section 30 with the arrangement of total internal reflection collimators 300 is shown. The light sources 4, located in front of the total internal reflection collimators 300, are also shown. A retardation film 325 and a reflective polarizer 324 for polarization recycling are arranged on the top surface of the light guide section 3. For better visualization, the retardation film 325 and the reflective polarizer 324 are shown as separate, spaced-apart layers. In practice, they can be stacked on the top surface of the light guide section. Light coupled out of the light guide section and passing through the reflective polarizer 324 serves as illumination light L. iThe illumination light Li passes through a diffuser film 322, which is positioned in front of a display panel 8, to be illuminated. The diffuser film 322 can be used, for example, to ensure the homogeneity of the illumination light L. ito further improve and modify the angular distribution of the light. The diffuser film 322 can additionally form a Fresnel lens. In this embodiment, the display panel 8 and the diffuser film 322 are arranged at an angle relative to the top of the light guide section of the light guide 3. This is particularly useful when the backlight unit 2 is used in a head-up display. To suppress sunlight reflections into the eyebox of a head-up display, the display panel 8 is inclined so that incident light is deflected towards a side wall of the head-up display. However, the light from an image-generating unit of the head-up display must be emitted along the line of sight. Therefore, it does not exit the display panel 8 vertically, but at an angle.

[0040] Fig. Figure 6 shows a front view of a backlighting unit 2 according to a second embodiment, which uses a light guide 3 according to the invention. The embodiment largely corresponds to the embodiment of Fig. 5. In this embodiment, however, the display panel 8 and the diffuser film 322 are arranged parallel to the top of the light guide section of the light guide 3. In this example, an additional prism film 327 is arranged on the reflective polarizer 324 to direct the direction of the illumination light L. i to change. The prism foil 327 is optional and can also be omitted. In this case, the viewing direction is perpendicular to the display panel 8. As before, the various optical layers 322, 324, 325, 327 are shown as separate layers. In practice, they can be stacked on top of the light guide section.

[0041] Fig. Figure 7 shows a section through a display device 1, which has a backlight unit 2 with a light guide 3 according to the invention. The display device 1 comprises a housing 9 with a backplate 10. The housing 9 is sealed by a cover glass 7. In this example, the cover glass 7 is glued to a mounting element 6 of the housing 9. A display panel 8 is glued to the cover glass 7 and illuminated by the backlight unit 2. The backlight unit 2 comprises a light guide 3 according to the invention. An arrangement of light sources 4 is mounted on a side wall of the backplate 10. The light sources 4 are mounted on a circuit board 5 next to the light guide 3 such that they emit light in the direction of the light coupling section 30 of the light guide 3. For example, the light sources 4 can be front-emitting diodes, i.e., light-emitting diodes that emit from their top side.A cushion band 11 is arranged between the mounting element 6 of the housing 9 and the light guide 3 to prevent movement of the light guide 3 in a direction perpendicular to the display panel 8. Movement of the light guide 3 in a direction parallel to the display panel 8 can be prevented by projections of the backplate 10, which are located in . Fig. 7 are not shown.

[0042] Fig. Figure 8 shows a side view of the light guide 3, similar to Figure 8. Fig. 2 described. In contrast, here the top surface 320 and the bottom surface 321 are not aligned parallel to each other. They have a smaller thickness D adjacent to the light mixing section 31. Igsi on as the thickness D Igs in the area of ​​end surface 326.

[0043] Fig. Figure 9 shows a total internal reflection collimator 300, often also referred to as a TIR collimator, in a sectional view. In the following, a collimator is referred to as a total internal reflection collimator if it is based, at least in part, on total internal reflection (total reflection at an internal surface). A hybrid collimator that has both mirror-coated reflective surfaces and uncoated surfaces at which light rays are reflected by means of total internal reflection is thus also referred to here as a total internal reflection collimator. The total internal reflection collimator 300 is made of glass, Plexiglas, or another translucent material. A light source 4 is located on its left side. It is situated near a blind-hole-like recess 932, which is located on the underside of the total internal reflection collimator 300, its light-inlet side.In the illustrated embodiment, it has a rectangular cross-section with a side surface 9321 and a bottom surface 9322. A curved surface 933 adjoins the recess 932 radially outwards. The side of the total internal reflection collimator 300 facing away from the light source 4, where the light exits, has an annular surface 934 in its radially outer region, at the center of which is a convex surface 935.

[0044] Light source 4 produces a wide beam of light LB1. A central beam of light L1 leaves light source 4 in the main direction of propagation D. PIt enters the total reflection collimator 300 unrefracted through the base surface 9322 of the recess 932, passes through it, and exits at the convex surface 935. Since it is located on the central axis of symmetry of the total reflection collimator 300, it is not refracted here either. Another light ray L2 travels at an angle to the central axis of symmetry of the total reflection collimator 300 and enters the total reflection collimator 300 at an edge region of the base surface 9322. It is refracted slightly towards the central axis of symmetry. After passing through the total reflection collimator 300, it strikes the inner surface of the convex surface 935, specifically in its outer region, and is refracted there towards the central axis of symmetry. It exits the total reflection collimator 300 almost parallel to the direction of propagation D. PThe radially inner region of the total internal reflection collimator 300, with its convex surface 935, acts similarly to a converging lens. A light ray L3, which leaves the light source 4 at an angle significantly different from the main beam direction, enters the total internal reflection collimator 300 through the side surface 9321. There, it is refracted and subsequently exhibits an even greater angle to the main beam direction. It then strikes the inner surface of the curved surface 933, where it undergoes total internal reflection. After total internal reflection, it is already parallel to the main beam direction and exits the total internal reflection collimator 300 through the annular surface 934. In the illustration, the surface of the annular surface 934 is flat and perpendicular to the main beam direction; no refraction of the light ray L3 occurs, as it is already aligned parallel to the main beam direction.Total internal reflection at the inner surface of the curved surface 933 is achieved in the exemplary embodiment by ensuring that the corresponding critical angle for total internal reflection is not undershot. According to one variant, the curved surface 933 is mirrored on the inside, so that the total internal reflection is due to the mirroring. In this case, it is not necessary to observe the critical angle. This allows for a more flexible design of the shape of the curved surface 933 and, if applicable, other surfaces of the total internal reflection collimator 300. The figure also shows further rays that either exit the total internal reflection collimator through the convex surface 935, like light rays L1 and L2, or through the annular surface 934, like light ray L3.Surfaces 933, 934, 935, 9321, and 9322 are further selected such that a redistribution of the light rays incident on the total internal reflection collimator 300 leads both to a parallelization with respect to the main beam direction and to the illuminance, i.e., the luminous flux per area, being constant or nearly constant across the surface in the light beam LB2 after the light rays exit the total internal reflection collimator. The light beam LB2 exiting the total internal reflection collimator 300 then enters the light guide section 32, which is not shown here.

[0045] Fig. Figure 10 shows a light guide 3 in which the light coupling section 30 consists mainly of total internal reflection collimators 300 and transitions directly into the light guide section 32. The coupled light thus travels almost parallel to the top surface 320 and the bottom surface 321 of the light guide section 32 according to the propagation direction D. PLight rays that nevertheless strike the upper surface 320 or the lower surface 321 arrive there at an angle whose magnitude is greater than the angle of total internal reflection (also: critical angle, usually defined with respect to the normal to the surface) and are thus guided within the light-guiding section 32 until they are reflected at the inclined end surface 326. Light rays that still strike the upper surface 320 or the lower surface 321 from the inside at an angle greater than the angle of total internal reflection are reflected by these surfaces and are now guided in the light-guiding section 32 in the opposite direction to D. P guided. Guided light hits L g Upon reaching an output structure 3210, it is directed by this structure towards the top side 320 and there is output as light L out coupled out. Since the coupling structures 3210 do not extend over the full width of the light guide section 32 in some cases, a portion of the light L is also shown in the figure. gshown, which does not hit the right-hand output coupling structure 3210 in the figure, but is reflected from the bottom 321, and is only reflected from the left of the two output coupling structures 3210 shown towards the top 320. Reference numbers 1 Display device 2 Backlight unit 3 optical fibers 30 Light coupling section 300 Total Reflection Collimator 31 Light mixing section, conical 32 Light guide section 320 Top side of the light guide section 321 Underside of the light guide section 3210 coupling structure 3211 Slanted area 3212 Parallel Area 322 Diffuser film 323 Reflective coating 324 Reflective polarizer 325 Delay layer 326 End surface, inclined 327 Prism foil 328 side area 4 light sources 5 circuit board 6 Fastening element 7 Cover glass 8 Scoreboard 9 cases 932 Exclusion 9321 side surface 9322 floor area 933 curved surface 934 ring-shaped surface 935 convex surface 10 Backplate 11 Pillow strap d Igs , d Igsi Thickness of the light guide section d lis Thickness of the light coupling section D p Direction of spread LB1,LB2 light beam L1,L2,L3,L4 Light beam L i Lighting light L g Light guidance in light guide section I Igs Length of light guide section l Ims Length of light mixing section L out Light extraction from light guide section L r Reflected light L recRecycled light

Claims

[1] Light guide (3) for a backlighting unit (2), comprising: - at least one light coupling section (30), wherein this section has at least one arrangement of total reflection collimators (300); - a light guide section (32), wherein the light guide section (32) has a reflective inclined end surface (326), and wherein the light guide section (32) has a top surface (320) and a bottom surface (321), wherein the light guide section (32) is configured to guide the light (L3) coming from the light coupling section (30) within the light guide section (32) to the inclined end surface (326), and couples out the light (Lg) reflected from the inclined end surface (326) through the top surface (320). [2] Optical fiber (3) according to claim 1, wherein the light coupling section (30) has a first thickness (d lis ) has a second thickness (d Igs) has, and a conical light mixing section (31) is present, which connects the at least one light coupling section (30) and the light guiding section (32). [3] Optical fiber (3) according to claim 1 or 2, wherein the underside (321) of the optical fiber section (32) has output coupling structures (3210), wherein the output coupling structures (3210) have areas (3211) which are inclined relative to the underside (321) of the optical fiber section (32) and are configured such that they emit a fraction of the light (L) coming from the inclined end surface (326) within the optical fiber section (32). g ) to the top (320) of the light guide section (32). [4] Optical fiber (3) according to claim 3, wherein a length (l lms) and a tapering of the tapered light mixing section (31) and the inclination of the end surface (326) are designed such that, in conjunction with the output coupling structures (3210), the light coupled out of the light guiding section (32) (L out ) exhibits a narrow angular distribution. [5] Optical fiber (3) according to claim 3 or 4, wherein a density of the output coupling structures (3210) along a propagation direction (D p ) of the light (L) guided within the optical fiber section (32) and reflected from the inclined end surface (326) is designed such that the light coupled out of the optical fiber section (32) (L) out ) a substantially constant brightness distribution over the entire length (l lgs ) of the light guide section (32). [6] Light guide (3) according to one of the preceding claims, further comprising a diffuser film (322) arranged on or above the top surface (320) of the light guide section (32). [7] Light guide (3) according to one of the preceding claims, further comprising a reflective coating (323) arranged on the underside (321) of the light guide section (32). [8] Light guide (3) according to one of the preceding claims, further comprising a reflecting polarizer (324) arranged on the top side (320) of the light guide section (32). [9] Light guide (3) according to claim 8, further comprising a delay layer (325) arranged between the top surface (320) of the light guide section (32) and the reflecting polarizer (324). [10] Light guide (3) according to claim 8, wherein the light guide section (32) consists of a birefringent material. [11] Light guide (3) according to one of claims 8 to 10, wherein the output coupling structures (3210) have areas (3212) that run parallel to the underside (321) of the light guide section (32). [12] Backlighting unit (2) with a light guide (3) according to any one of claims 1 to 11, wherein the backlighting unit (2) further comprises at least one arrangement of light sources (4), wherein the light sources (4) are configured to emit light in the direction of the total reflection collimators (300). [13] Display device (1) with the backlight unit (2) according to claim 12, wherein the display device (1) further comprises a display panel (8) configured to be illuminated by light (L out ) is illuminated, which is provided by the backlight unit (2). [14] Display device (1) according to claim 13, wherein the display device (1) is configured to be used in a head-up display or to provide switchable privacy functionality. [15] Display device (1) according to claim 13 or 14, further comprising a prism film (327) configured to direct the illumination light coming from the backlight (2) in one direction (L i ) changes.

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