Light guide for a backlight, backlight, and display device

Abstract

The invention relates to a light guide (3) for a backlight unit (2). The light guide has at least one light-coupling portion (30) with a first thickness (dlis), the light coupling portion having at least one array of total reflection collimators (300). The light guide (3) also has a light-guiding portion (32) with a second thickness (dlgs) which is smaller than the first thickness (dlis), the light-guiding portion (32) having an upper face (320) and a lower face (321) and the light-guiding portion (32) being configured such that it couples out the light (Lg) guided within the light-guiding portion (32) through the upper face (320). The light guide (3) also has a conical light-mixing portion (31) which connects the at least one light-coupling portion (30) and the light-guiding portion (32), the light-mixing portion (31) and the light-guiding portion (32) being inclined with respect to one another by an angle of inclination (α) which is greater than zero degrees.

Description

[0001] Description

[0002] Light guide for a backlight, a backlight and a display device

[0003] 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.

[0004] 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.

[0005] Modern backlight units are mostly based on edge-illuminated light guides, into which the light from multiple light-emitting diodes (LEDs) is coupled via a side surface of the light guide. The light propagates through the light guide by total internal reflection and is coupled out again by special output structures on the surface of the light guide or by a specific choice of light guide geometry, such as a conical light guide. 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. There are also variants that collimate the coupled-in light. 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 such that a portion of the guided light is scattered as emitted light from the optical fiber. The conical collimator is configured to collimate the light supplied by a light source and then transmit this collimated light as guided light to the optical fiber.

[0006] 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.

[0007] 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.

[0008] The typical beam pattern of an edge-lit backlight system exhibits 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 angle and a clearly 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 variety of light sources and some collimation optics. This configuration makes it possible to achieve narrow light distributions.However, in order to achieve acceptable homogeneity, the space requirement for the lighting system is significantly larger compared to edge-lit systems.

[0009] It is an object of the present invention to provide a compact edge-illuminated backlight unit for a display device with light of a narrow angular distribution, high efficiency and homogeneous illumination.

[0010] This problem is solved by a light guide according to claim 1, by a backlighting unit according to claim 10, and by a display device according to claim 11. The dependent claims include advantageous further developments and improvements of the present principles, as described below.

[0011] From a first perspective, a light guide for a backlighting unit exhibits the following characteristics:

[0012] - at least one light coupling section with a first thickness, wherein this section has at least one arrangement of total reflection collimators;

[0013] - a light-guiding section with a second thickness that is smaller than the first thickness, wherein the light-guiding section has a top and a bottom, wherein the light-guiding section is configured to couple out the light guided within the light-guiding section through the top; and

[0014] - a conical light mixing section connecting the at least one light coupling section and the light guiding section, wherein the light mixing section and the light guiding section are arranged inclined to each other by an angle of inclination greater than zero degrees.

[0015] 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 total internal reflection 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.

[0016] Total internal reflection collimators are particularly advantageous because they are able to collect the light emitted by light-emitting diodes with high efficiency and to restrict the collected light to a small angular range.

[0017] According to the invention, the collimated light passes through the light mixing section. Due to the sufficiently long light path, adequate mixing of the light from different light sources takes place. At the transition from the light mixing section to the inclined light guiding section, the propagation angle in the light guiding section is also changed so that the light is still guided by total internal reflection, but simultaneously strikes the top or bottom surface at a significantly steeper angle. For example, suitably designed microstructures are provided on the bottom surface by means of which incident light is reflected to the top surface and thereby coupled out of the light guiding section.

[0018] In an advantageous embodiment, the light mixing section has a first surface and a second surface, one of which is aligned parallel to the top surface of the light guide section. The light mixing section and the top surface thus abut flush, which is advantageous when installation space is limited. In another advantageous embodiment, the light mixing section has a first surface and a second surface, one of which is aligned parallel to the underside of the light guide section. The light mixing section and the underside thus abut flush, while the light mixing section and the light coupling section project beyond the top surface. If a further component, such as a display panel to be backlit, is subsequently arranged on the top surface, a flush arrangement can also be achieved on this side, which is advantageous when installation space is limited.

[0019] In an advantageous embodiment, the length of the light mixing section and the angle of inclination between its first and second surfaces are coordinated such that the collimated light is reflected from these surfaces only as often as necessary to prevent it from falling below the critical angle for total internal reflection. This allows for a long light mixing section, resulting in good light mixing. It also permits a relatively large distance between the light sources and the light guide section without causing scattering losses due to falling below the critical angle for total internal reflection. Such a relatively large distance is often desirable for reasons of space optimization or heat dissipation from the light sources.

[0020] In an advantageous embodiment, each ray of light passing through the light mixing section is reflected at most once within the section. This enables a particularly compact design while simultaneously ensuring the most homogeneous possible distribution of light within the light guide section.

[0021] In an advantageous embodiment, the transition from a surface of the light mixing section to the top or bottom of the light guiding section is a curved surface. Advantageously, the curvature can be designed such that the critical angle for total internal reflection is avoided in this area as well.

[0022] The array of total internal reflection collimators is connected to a light guide section via the light mixing 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 or light mixing section with a light coupling section. The light guide can also be made entirely of glass.

[0023] 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.

[0024] In an advantageous embodiment, the length and taper of the tapered light mixing section, as well as optionally the tilting of the light coupling section and the light mixing section relative to each other, are designed such that, in conjunction with the output coupling structures, the light coupled out of the light guide path exhibits a narrow angular distribution. By correctly designing the conical light mixing section, optionally the aforementioned tilting, and the output coupling structures, the angular distribution of the light can be very precisely controlled.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] In an advantageous embodiment, the light guide further comprises a reflective polarizer arranged on or above the top surface of the light guide section. If the top and bottom surfaces of the light guide section are arranged parallel to each other, this 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.

[0029] 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.

[0030] In an advantageous embodiment, light coupling sections and conical light mixing sections are arranged on two adjacent sides, usually at right angles to each other, or on two opposite sides of the light guide section. 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] Further features of the present invention will become apparent from the following description and the attached claims in conjunction with the illustrations.

[0035] Fig. 1 shows a perspective view of a light guide according to the invention;

[0036] Fig. 2 shows a side view of the light guide of Fig. 1;

[0037] Fig. 3 shows a front view of a light coupling section from the optical fiber of Fig. 1;

[0038] Fig. 4 illustrates light paths and decoupling structures of the optical fibers of Fig. 1; Fig. 5 shows a front view of a backlighting unit according to a first embodiment, which incorporates an optical fiber according to the invention;

[0039] Fig. 6 shows a front view of a backlighting unit according to a second embodiment, which incorporates a light guide according to the invention;

[0040] Fig. 7 shows a section through a display device including a backlight unit with a light guide according to the invention;

[0041] Fig. 8 shows a side view of the light guide;

[0042] Fig. 9 shows a side view of the light guide; and

[0043] Fig. 10 shows a total reflection collimator.

[0044] Detailed description

[0045] 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.

[0046] All examples and conditional formulations reproduced herein are intended for illustrative purposes, to help the reader understand the principles of the disclosure and the concepts that the inventor has contributed to the advancement of the technology, and are to be interpreted as not being limited to the specifically cited examples and conditions. 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, that is, all developed elements that perform the same function regardless of their structure.

[0047] For example, experts will understand that the diagrams presented herein represent conceptual views that embody the principles of revelation.

[0048] Fig. 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. 2. The optical fiber 3 comprises 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 düs and includes an arrangement of total internal reflection collimators 300. A front view of the light coupling section 30 and the arrangement of the total internal reflection collimators 300 is shown in Fig. 3. The light guiding section 32 has a length li gsand a second thickness digs, which is smaller than the first thickness diis. The conical light mixing section 31 has a length hms and connects the light coupling section 30 and the light guiding section 32. The light mixing section 31 has a first surface 311 and a second surface 312, which form a wedge, also referred to here as the conical shape of the light mixing section 31. The two surfaces 311, 312 have a wedge angle β to each other, which preferably has a value in the range 20° < β < 40°. The central plane ZE1 of the light mixing section 31 and the central plane ZE2 of the light guiding section 32 are arranged inclined to each other, i.e., not parallel. The inclination angle α > 0° is shown. 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 that is guided within the light guide section 32 and reaches the end surface 326. While in Fig. 1 and Fig. 2 only a light coupling section 30 and a 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 or on the end surface 326.

[0049] Fig. 4 shows light paths and coupling structures 3210 of the optical fiber 3 from Fig. 1. The light L g , which is guided within the light guide section 32 of the light guide 3, runs inclined to a propagation direction D PThe output structures 3210 are arranged in a base surface 321 of the light guide section 32 of the light guide 3. 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 the light L g , which corresponds to the direction of propagation D P guided at an angle within the light guide section 32, it is directed to the top 320 of the light guide section 32, where it at least partially leaves the light guide section 32 and thus forms coupled-out light Lout.

[0050] The output coupling structures 3210 also have regions 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. With the aid of a retardation layer 325, the polarization state of the reflected light Lr is converted into a usable polarization state upon retroreflection at the underside 321. The resulting recycled light Lrec is now able to pass through the reflecting polarizer 324. The retardation layer 325 can be implemented, for example, as a retardation foil, a retardation film, or a retardation coating.

[0051] The length and taper of the conical mixing section 31 of the optical fiber 3, as well as the angle of inclination α between the mixing section 31 and the optical fiber section 32, 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 Lout coupled out of the light guide section 32 has a substantially constant brightness distribution over the entire length of the light guide section 32.

[0052] Fig. 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 Li.The 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 further improve the homogeneity of the illumination light Li and to modify the angular distribution of the light. The diffuser film 322 can also form a Fresnel lens. In this embodiment, the display panel 8 and the diffuser film 322 are positioned 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 tilted so that incident light is deflected toward 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 viewing direction.Therefore, it does not leave scoreboard 8 vertically, but at an angle.

[0053] Fig. 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. This embodiment largely corresponds to the embodiment of Fig. 5. However, in this embodiment, the display panel 8 and the diffuser film 322 are arranged parallel to the top surface 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 change the direction of the illumination light Li. The prism film 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 the top surface of the light guide section.

[0054] Fig. 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. The circuit board 5 is arranged at an angle corresponding to the inclination of the light mixing section 31 or the light coupling section 30.For example, the light sources 4 can be front-emitting diodes, i.e., LEDs 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 on the backplate 10, which are not shown in Fig. 7.

[0055] Fig. 8 shows a side view of the light guide 3, similar to that described in Fig. 2, in the area of ​​light coupling. One of the light sources 4, the subsequent light coupling section 30, and the subsequent light mixing section 31 are visible. The light mixing section has a first surface 311 and a second surface 312. These surfaces form interfaces at which light traveling in the light guide is totally reflected when it strikes one of these interfaces at an angle exceeding the critical angle for total internal reflection, also called the angle of total internal reflection. In this embodiment, the axes of symmetry SYM0 of all total internal reflection collimators 300 are aligned parallel to each other and form a central plane ZE0 of the light coupling section 30. The central plane ZE0 of the light coupling section 30 is tilted relative to the central plane ZE1 of the light mixing section 31 by a tilt angle y.

[0056] In this embodiment, the tilt angle y is selected such that the collimated light coming from the light coupling section 30 travels essentially parallel to the second surface 312, i.e., is almost not reflected at this surface. In other embodiments, not shown here, different values ​​for the tilt angle y can be selected. It is also within the scope of the invention to select different tilt angles y for different collimators 300. The light mixing section 31 is adjoined by the light guiding section 32 with its upper surface 320 and its lower surface 321. The central axes or central planes of the light mixing section 31 and the light guiding section 32 are arranged at an angle α to each other. The area of ​​the lower surface 321, in which output coupling structures 3210 are located, is also visible. The output coupling structures 3210 are so small that they are barely discernible in this illustration.It can further be seen that the light mixing section 31 and the light guiding section 32 are inclined relative to each other. In the embodiment shown here, the first surface 311 of the light mixing section 31 and the upper surface 320 of the light guiding section 32 are aligned parallel to each other. The second surface 312 and the lower surface 321 thus exhibit twice the value 2*a of the angle of inclination α by which the central planes of the light mixing section 31 and the light guiding section 32 are inclined relative to each other; the axis of symmetry SYM0 of a total internal reflection collimator 300 is therefore tilted by a compound angle α+α relative to the central plane ZE2 of the light guiding section 32.

[0057] Fig. 9 shows a similar side view to Fig. 8, except that here the second surface 312 of the light mixing section 31 and the underside 321 of the light guide section 32 are arranged parallel to each other. A display panel 8 is shown on the upper surface 320 of the light guide section 32. It can be seen that the total thickness of the light guide section 32 and the display panel 8, and any other components located on or between them (not shown individually here), corresponds approximately to the maximum thickness of the light mixing section 31. Due to the angled arrangement of the light mixing section 31 and the light guide section 32 relative to each other, there is no increase in thickness that would require additional installation space. Furthermore, some exemplary light rays are shown in this figure.It can be seen that the collimated light coming from the light coupling section 30 travels essentially parallel to the first surface 311 of the light mixing section 31, and that the opening angles of the first surface 311 and the second surface 312, which form the conical shape of the light mixing section 31, are coordinated such that light rays of the collimated light are reflected at most once at the second surface 312 before entering the light mixing section 32, at whose top 320 and bottom 321 they are reflected and thus guided. An example of a single ray S1 can also be seen, which is reflected at an output coupling structure 3210 (not visible here), then couples out through the surface 320, and passes through the display panel 8. Most of the coupled-out rays, like this ray S1, travel perpendicularly through the display panel 8.However, there is also a negligible number of beams that do not ideally hit an output coupling structure, and then, like the example beam S2 shown, hit the display board 8 at an oblique angle.

[0058] An optical fiber 3 according to the invention with directed emission features input collimation of the light. However, in conventional optical fibers of this type, the thickness of the fiber limits the size of the collimators that can be used and thus the possibility of achieving very good collimation of the light. Furthermore, collimated light coupled into the optical fiber at near 0° cannot be coupled out by a microstructure arranged on a surface after a single passage through the optical fiber, since no interaction with the surface occurs. Therefore, some of the light remains in the optical fiber and exits at the rear. An optical fiber 3 according to the invention enables an extremely compact, edge-illuminated backlight unit for display units with narrow light distribution, high efficiency, and homogeneous illumination.According to the invention, a collimation area is provided as the light coupling section 30, which is thicker than the actual light guide section 32 of the optical fiber 3 and thus enables better collimation. To still guide the light into the light guide section 32, the optical fiber 3 tapers down from the light coupling section 30 towards the light guide section 32. To prevent the problems described in the prior art from occurring to a significant degree, the light is not collimated at 0°, i.e., parallel to the light guide section 32, according to the invention. Instead, the collimators 300 are inclined by a specific angle y, which, depending on the design of the optical fiber 3, is, for example, y = 15°, and the light is coupled into the optical fiber 3 at this angle y.This means that no light is present on the axis of the light guide section 32 (parallel to the main plane of the light guide 3), which would otherwise be impossible to extract and lead to efficiency problems. This results in higher overall efficiency and less light is extracted unused. One solution according to the invention provides for an inclination angle α between the light mixing section 31 and the light guide section 32. A combination of inclination angle α and tilt angle α also represents a useful further development of the invention.

[0059] According to the invention, to prevent certain rays from exhibiting an angle smaller than the critical angle of total internal reflection, for example after passing through the light mixing section 31 when coupled into the light guide section 32, and thus being directly coupled out, the light mixing section is designed accordingly. The connecting piece between the collimators 300 and the light guide section 32, which corresponds to the light mixing section 31, is designed such that the collimated light is only reflected at the outer edges, the surfaces 311, 312, as often as necessary to ensure that it does not fall below the critical angle of total internal reflection.In a simple embodiment, this wedge-shaped connecting piece, the light mixing section 31, exhibits a maximum of only one reflection at the outer wall, the surface 311, 312, per beam. The wedge shape is formed by the angular deflection of the collimators 300 in conjunction with the extension of the light guide section 32 by the light mixing section 31. Thus, the coupled-in light is controlled solely by its impact on the microstructures 3210 and is not coupled out due to falling below the critical angle for total internal reflection, thereby improving homogeneity and efficiency. Other forms of angled coupling are also within the scope of the invention. These coupling forms can also have curved surfaces.

[0060] According to the invention, at least one of the following advantages is achieved: increased homogeneity, increased efficiency, improved thermal behavior, compact installation space, flexible selection of the side for light coupling from the light sources, good light mixing, and minimal interference. The invention is advantageously applicable to all display and head-up display systems that require a narrow light distribution.

[0061] Fig. 10 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.

[0062] The light source 4 produces a wide beam of light LB1. A central light ray L1 leaves the light source 4 in the main direction of propagation Dp. It enters the total internal reflection collimator 300 without refracting 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 internal reflection collimator 300, it is not refracted there either. Another light ray L2 travels at an angle to the central axis of symmetry of the total internal reflection collimator 300 and enters the total internal reflection collimator 300 at an edge region of the base surface 9322. Here, it is refracted slightly towards the central axis of symmetry. After passing through the total internal 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 internal reflection collimator 300 almost parallel to the direction of propagation Dp. The 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. Here, 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 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 undercut. 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.

[0063] Reference numbers

[0064] 1 Display device

[0065] 2 Backlight unit

[0066] 3 fiber optic cables

[0067] 30 Light coupling section

[0068] 300 Total Reflection Collimator

[0069] 31 Light mixing section, conical

[0070] 311 first surface of the light mixing section

[0071] 312 second surface of the light mixing section

[0072] 32 Light guide section

[0073] 320 Top side of the light guide section

[0074] 321 Underside of the light guide section

[0075] 3210 coupling structure

[0076] 3211 Slanted area

[0077] 3212 Parallel Area

[0078] 322 Diffuser film

[0079] 323 Reflective coating

[0080] 324 Reflective polarizer

[0081] 325 Delay layer

[0082] 326 End surface, inclined

[0083] 327 Prism foil

[0084] 328 side area

[0085] 4 light sources

[0086] 5 circuit board

[0087] 6 Fastening element

[0088] 7 Cover glass

[0089] 8 Scoreboard

[0090] 9 cases

[0091] 932 Exclusion

[0092] 9321 Side surface 9322 Floor surface

[0093] 933 curved surface

[0094] 934 ring-shaped surface

[0095] 935 convex surface

[0096] 10 Backplate

[0097] 11 Cushion band digs, dlgsi Thickness of the light guiding section dlis Thickness of the light coupling section

[0098] D P Direction of spread

[0099] LB1.LB2 Light beam

[0100] L1, L2, L3, L4 Light beam

[0101] Li lighting light

[0102] Lg light guidance in light guide section llgs length of light guide section

[0103] Ilm's length light mixing section

[0104] Lout light extraction from light guide section

[0105] Lr Reflected Light

[0106] Lrec Recycled Light

[0107] S1, S2 beam

[0108] SYMO axis of symmetry

[0109] ZE0, ZE1, ZE2 central plane a inclination angle β wedge angle

[0110] Y tilt angle

Claims

Patent claims 1. Light guide (3) for a backlighting unit (2), comprising: - at least one light coupling section (30) with a first thickness (düs), wherein this has at least one arrangement of total reflection collimators (300); - a light-guiding section (32) with a second thickness (digs) that is smaller than the first thickness (düs), wherein the light-guiding section (32) has a top (320) and a bottom (321), wherein the light-guiding section (32) is configured to couple out the light (Lg) guided within the light-guiding section (32) through the top (320); and - a conical light mixing section (31) connecting the at least one light coupling section (30) and the light guiding section (32), wherein the light mixing section (31) and the light guiding section (32) are arranged inclined to each other by an angle of inclination (a) greater than zero degrees.

2. Light guide (3) according to claim 1, wherein the light mixing section (31) has a first surface (311) and a second surface (312), one of which is aligned parallel to the top (320) of the light guide section (32).

3. Light guide (3) according to claim 1, wherein the light mixing section (31) has a first surface (311) and a second surface (312), one of which is aligned parallel to the underside (321) of the light guide section (32).

4. Optical fiber (3) according to one of the preceding claims, wherein the length (Ilms) of the light mixing section (31 ) and the angle of inclination (β) between its first surface (311 ) and its second surface (312) are matched such that the collimated light is only reflected in a controlled manner from these surfaces (311 ,312) until coupling, such that it does not fall below the critical angle of total internal reflection.

5. Light guide (3) according to claim 4, wherein each ray of the light passing through the light mixing section (31) is reflected at most once in the light mixing section (31).

6. Light guide (3) according to one of the preceding claims, wherein the transition from a surface (311 ,312) of the light mixing section (31 ) to the top (320) or the bottom (321 ) of the light guiding section (32) is a curved surface ( ).

7. Optical fiber (3) according to one of the preceding claims, wherein the underside (321) of the optical fiber section (32) has output coupling structures (3210), wherein the output coupling structures (3210) have regions (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) guided within the optical fiber section (32). g ) to the top (320) of the light guide section (32).

8. Light guide (3) according to claim 3, wherein the length (hms) and a tapering of the tapered light mixing section (31) are designed such that, in conjunction with the coupling structures (3210), the light (Lout) coupled out of the light guide section (32) has a narrow angular distribution.

9. Optical fiber (3) according to claim 7 or 8, 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) is designed such that the light (Lout) coupled out of the optical fiber section (32) has a substantially constant brightness distribution over the entire length (h) gs ) of the light guide section (32).

10. Backlighting unit (2) with a light guide (3) according to any one of claims 1 to 9, 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).

11. Display device (1) with the backlight unit (2) according to claim 10, wherein the display device (1) further comprises a display panel (8) configured to be illuminated by light (Lout) provided by the backlight unit (2).

12. Display device (1) according to claim 11, wherein the display device (1) is configured to be used in a head-up display or to provide switchable privacy functionality.

13. Display device (1 ) according to claim 11 or 12, further comprising a prism foil (327) configured to change the direction of the illumination light (Li) coming from the backlight (2).

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