Optical device and display panel

Abstract

The present disclosure relates to an optical device (1) for controlling light, the optical device (1) comprising: a first waveguide (2) for receiving a light beam from an external light source; at least a second waveguide (3); an optical coupler (4) for coupling the light beam from the first waveguide (2) to the second waveguide (3); a beam shaping structure (5) having a light emitting area (6) for emitting the light beam, wherein the second waveguide (3) is configured to guide the light beam coupled from the first waveguide (2) to the beam shaping structure (5), wherein the beam shaping structure (5) is configured to propagate the light beam received from the second waveguide (3) to the light emitting area (6) such that a beam divergence of the light beam emitted from the light emitting area (6) is lower than a beam divergence of the light beam received from the second waveguide (3).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an optical device for controlling light, the optical device comprising:

[0002] a first waveguide for receiving a light beam from an external light source,

[0003] at least one second waveguide,

[0004] a light coupler for coupling the light beam from the first waveguide to the second waveguide,

[0005] a beam shaping structure having a light emitting area for emitting the light beam,

[0006] wherein the second waveguide is configured to guide the light beam coupled from the first waveguide to the beam shaping structure. Furthermore, the present disclosure relates to a backlight unit and a display panel. BACKGROUND

[0007] Some optical devices are known that distribute light over a larger area. This is for example necessary for backlight units of liquid crystal displays (LCD).

[0008] LCDs are by far the most widely used display technology and can be found in everything from smartphones to televisions. In an LCD, a backlight unit, in particular a planar light source, illuminates all the pixels, which then each act as a shutter, letting light through or partially blocking the light through that pixel. The shutter is based on the polarization of the light. The light rays emitted by the backlight first pass through a bottom polarizer and are polarized. The liquid crystal provides a voltage-controlled way to change the polarization of such light rays: the liquid crystal is birefringent and an electric field can be used to adjust the orientation of the liquid crystal. After leaving the liquid crystal, the light rays hit a top polarizer (also called an analyzer), the transmission of which depends on the polarization angle imprinted on the light rays in the liquid crystal.

[0009] Ideally, a display should show the same image independent of the viewing angle. To achieve this, the pixels should radiate uniformly in all directions. While this is standard for emissive display technologies like OLEDs, it is not the case for transmissive technologies like LCDs: the light rays observed from an observer originate from the backlight at the bottom of the LCD display stack. The liquid crystal layer then modulates the intensity of this light to change the brightness of the pixel.

[0010] For light rays that propagate through the display stack at non-normal angles, the path length of the liquid crystal cell and the birefringent axis seen by the light rays change, so the polarization rotation that encodes the brightness is different from the light rays that propagate at normal angles. This results in a change in brightness of the pixel if the display is viewed from different angles.

[0011] A possibility to overcome this problem is to use a backlight that emits light only at the normal angle (collimated backlight) and then use a diffuser on top of the display stack. Nonetheless, this is usually not done because there is no effective collimated backlight in the state of the art.

[0012] For example, US 2018 / 0292713 A1 shows a backlight display with light sources. The display can include a side-lit light guide in which light emitted from the light sources is distributed laterally within the light guide and scattered out of the light guide by out-coupling structures such as gratings, protrusions or grooves. Optionally, the display includes a plurality of adjacent light emitting diodes with curved reflectors for collimating light. To help further collimating the light, the light sources are provided with a light filtering layer having an angle-dependent light transmission characteristic for reflecting off-axis light. However, this leads to high energy losses and does not allow for a low beam divergence, resulting in cross-talk between different sub-pixels.

[0013] Another display is shown in US 2016 / 0300535 A1. An array of laser diodes is provided which directly emit light in the direction of the pixels. The light emitted by the laser diodes is first dispersed by a lens and then collimated by a Fresnel lens. However, this approach requires a large number of laser diodes to illuminate the display area and does not allow for a thin backlight unit.

[0014] Another optical device is shown in EP 3599541 A1. The device includes a substrate and light waveguides extending within the substrate, each of which is bent towards the substrate surface. In another embodiment, the waveguides can direct light to a wedge in the substrate which forms a flat mirror surface to scatter the light out of the substrate. However, in this process the divergence of the emitted light beam increases, resulting in a very large angle of divergence.

[0015] US 7773849 B2 shows an apparatus for optical resizing or backlighting of an LCD. Optical resizing refers to the expansion or contraction of the area occupied by an optical wavefront. Therein, for magnification purposes, an image is directed through a waveguide bundle extending from a small facet to a large facet.

[0016] US 2008 / 144333 A1 shows a light guide apparatus including a substrate having a plurality of light emitting portions and a plurality of light guides printed thereon, the light guides being optically coupled to the light emitting portions.

[0017] WO 2015 / 000965 A1 describes an integrated optical solution for a lighting apparatus having a coupling-out unit coupling laser light from a primary waveguide to a plurality of secondary waveguides.

[0018] EP 3599541 A1 relates to an optical device for controlling light and an optical touch sensing device, both having optical waveguides formed in a transparent substrate by direct laser writing.

[0019] US 2019 / 369213 A1 shows an optical system having a plurality of optical devices carried by an optical body. Optical waveguides extend within the optical body between the respective optical devices and an imaginary curved surface within the optical body. A controller selectively operates the plurality of optical devices to produce at least one light beam. SUMMARY

[0020] It is an object of the present disclosure to solve or alleviate at least some of the problems of the prior art. In particular, the present disclosure shall provide an optical device which can be used for example in a backlight unit and which efficiently provides at least one light beam having a reduced beam divergence. Optionally, the optical device comprises the possibility to provide a further collimated light beam.

[0021] The present disclosure proposes an optical device as initially described, wherein the beam shaping structure is configured to propagate the light beam received from the second waveguide to the light emitting area such that the beam divergence of the light beam emitted from the light emitting area is lower than the beam divergence of the light beam received from the second waveguide.

[0022] By guiding the light beam in different waveguides to the beam shaping structure, the angle of incidence and other properties of this light beam can be precisely adjusted such that the beam divergence is reduced by the beam shaping structure. This is not possible when the light is distributed chaotically in a large plate-like substrate, where the light does not impinge on the optical elements in a well-defined manner. In this way, the proposed optical device can provide a collimated light beam without having to purposefully discard a portion of the light beam, thereby reducing the luminance and wasting energy. Using this light beam, small dots (e.g. individual sub-pixels of a display) can be illuminated. Thus, when used for a display, a 1-to-1 relationship of waveguides and sub-pixels can be provided; i.e. the light beam leaving the waveguide and being guided to the beam shaping structure illuminates only a single sub-pixel and vice versa, each sub-pixel is illuminated by a light beam arriving at the beam shaping structure from a single waveguide. The beam shaping structure can be shared between multiple sub-pixels and their respectively associated waveguides. Furthermore, the optical device provides the possibility to provide a further collimated light beam originating from the same external light source, as a further waveguide can branch off from the first waveguide. Typically, the first waveguide can receive the light beam from the external light source directly or indirectly, e.g. by one or more additional intermediate waveguides and / or one or more additional intermediate light couplers.

[0023] The optical device is characterized in that the beam shaping structure is configured to propagate the light beam received from the second waveguide to the light emitting area such that the light beam emitted from the light emitting area has a lower beam divergence than the light beam received from the second waveguide, which means that the beam divergence along at least one axis of the light beam is reduced. The beam divergence angle is a measure of the increase of the beam width or beam diameter with increasing distance from the beam waist position, which is defined in ISO 11146-1 (first edition, 2005-01-15), in particular in section 3.15 of the above mentioned document for astigmatic and simple astigmatic beams; for general astigmatic beams the corresponding definitions in ISO 11146-2 and ISO 11146-3 apply. Optionally, the beam divergence angle is reduced for both principal axes of the light beam. For at least one axis, optionally for both / all axes, of the light beam the beam divergence angle is reduced optionally by at least 1°, further optionally by at least 10°, further optionally by at least 20°. Optionally, the divergence angle is reduced such that the light beam emitted from the light emitting area has a divergence half angle of less than 10°, further optionally less than 3°, further optionally less than 1°. The divergence angle is reduced such that the diameter of the light beam spot at a distance of 2 cm from the light emitting area (and / or from the optical shaping element mentioned below) is optionally less than 2 mm, further optionally less than 500 pm, further optionally less than 100 pm. In particular, when used in a corresponding backlight unit, the optical device of the present disclosure allows to generate light spots on the surface of the display and / or on the liquid crystal layer of the display with a diameter of less than 20 pm, which is less than the sub-pixel pitch of a TV (typically more than 70 pm), even of a smartphone (about 25 pm).

[0024] Optionally, the beam shaping structure collimates and / or (re)focusses the light beam. When the optical device is used in a backlight of a display, thereby one light beam can be generated for each sub-pixel. Optionally, the first waveguide and / or the second waveguide is a single mode waveguide. Advantageously, if the waveguide core diameter of the first and / or second waveguide is less than 100 pm, optionally between 0.1 pm and 50 pm, further optionally between 1 pm and 5 pm.

[0025] Optionally, the optical arrangement comprises a plurality of further waveguides having a corresponding number of further light couplers for coupling light beams from the first waveguide to respective further waveguides, wherein each of the plurality of further waveguides is configured to direct a light beam coupled from the first waveguide to the light beam shaping structure, wherein the light beam shaping structure is configured to propagate a light beam received from each of the plurality of further waveguides to the light emission area such that the beam divergence of the light beam emitted from the light emission area is lower than the beam divergence of the light beam received from the respective waveguide. The further light couplers can also be used to couple light beams from other waveguides that are directly or indirectly connected to the first waveguide and / or can be connected to an external light source and / or can be connected to other external light sources. The number of further waveguides is optionally at least 1, further optionally at least 10, further optionally at least 100, further optionally at least 10000, further optionally at least 100000. Thus, each sub-pixel can have one waveguide and light from one external light source can be distributed to hundreds or thousands or millions of pixels using directional couplers. It is even more advantageous if the optical arrangement comprises further waveguides of the first waveguide type for receiving light beams from an external light source and / or from further external light sources. For example, each external light source can be coupled to at least 1000 further waveguides (second waveguide type).

[0026] Optionally, the light beam reaching the light beam shaping structure from the second waveguide is propagated such that the light beam only illuminates a part of the light emission area.

[0027] Optionally, the light beams propagated by the light beam shaping structure from different ones of the further waveguides illuminate non-overlapping parts of the light emission area and / or the overlap of each two adjacent parts comprises less than 10% of the light beam energy from the different waveguides. Optionally, the light emission area is substantially planar and / or in a plane.

[0028] It should be noted that the application of collimated backlights extends beyond the scope detailed here. Collimated backlights are also needed in the emerging field of light field displays and holographic displays to improve image quality.

[0029] The present disclosure also provides alternative embodiments generally:

[0030] An optical arrangement for controlling light and for a backlight unit of a display, the optical arrangement comprising:

[0031] at least one waveguide;

[0032] a light beam shaping structure having a light emission area for emitting a light beam;

[0033] The beam shaping structure is adapted to propagate the light beams arriving from one of the waveguides so that the light beams illuminate a single sub-pixel of the display area of the display. More specifically, as explained with respect to the first embodiment, there is a one-to-one relationship between the waveguides and the sub-pixels. Each light beam arriving at the beam shaping structure is propagated to a different sub-pixel, depending on which waveguide it comes from. The optical device of this alternative embodiment can comprise the features of the optical device described above, wherein the waveguide of the alternative embodiment corresponds to the second waveguide, and it can comprise any of the optional features listed below. Thus, the optional embodiments listed below refer both to the optical device mentioned in the previous paragraph and to the optical device mentioned in this paragraph.

[0034] In an exemplary embodiment, the beam shaping structure comprises an optical shaping element, wherein at least the second waveguide directs the light beam coupled from the first waveguide to the optical shaping element. Optionally, the further waveguides direct the light beams coupled from the respective further waveguides to said optical shaping element. Advantageously, the optical device comprises a further optical shaping element, wherein each of the plurality of further waveguides directs a light beam to the optical shaping element or one of the further optical shaping elements. The optical shaping element operates on the light beam when it propagates from the second waveguide to the light emitting area to reduce the light beam divergence.

[0035] In a more specific exemplary embodiment, the optical shaping element is a concave mirror or a diffractive optical element. This allows to particularly easily implement the optical shaping element and the optical shaping structure comprising the optical shaping element. Optionally, the concave mirror is a micromirror. The concave mirror can have a high surface quality, otherwise the light beam quality can be affected and the focal spot can be enlarged. The concave mirror can have an arbitrary shape, wherein there can be sharp bends. Optionally, the concave mirror has a bending radius (or a plurality of bending radii) between 0.1 mm and 1 mm, further optionally between 0.3 mm and 0.7 mm. It can be used to set the light beam diameter at any defined distance as needed, e.g. at any point in the display stack, e.g. in the liquid crystal layer or the light converting (e.g. quantum dots or quantum rods) layer of the display. If the optical shaping element is a concave mirror, further optionally, the further waveguides illuminate the same concave mirror. For example, the maximum number of waveguides illuminating the same mirror can be set to 25. The concave mirror can have a shape of e.g. spherical, parabolic or toroidal. The optical shaping element, in particular the concave mirror, can be produced e.g. by a roll-to-plate process, which makes the manufacturing cost inexpensive. Furthermore, precision glass press molding or dry etching are also possible manufacturing techniques.

[0036] The optical shaping element can have at least a first axis and a second axis, wherein the focal length of the first axis of the optical element is different from the focal length of the second axis. The optical shaping element can receive the light beam from the second waveguide from a direction different from the direction in which the light beam is emitted / reflected from the optical shaping element, e.g. the light is directed towards the optical shaping element at a shallow angle of e.g. 10-20°. Providing different focal lengths for each axis allows to compensate for distortions caused by such angles of incidence, e.g. transforming an elliptical light beam into a circular light beam, and generally transforming the light beam such that the resulting light beam has a more similar beam width for different (principal) axes. The first axis is optionally orthogonal to the second axis. If the optical shaping element is a concave mirror, it can have different radii of curvature on the first and second axis.

[0037] Optionally, the optical shaping element can be provided by a polymer structure. In this way, high beam quality and high reflectivity can be achieved. For example, the polymer structure is a UV nanoimprinted polymer structure. Optionally, the optical shaping element and / or the polymer structure comprises a reflective coating (e.g. silver), respectively. This allows the optical shaping element to be particularly easy to implement and have low losses. The reflective coating can have a thickness of e.g. between 10 pm and 100 pm.

[0038] In an optional embodiment, the optical device comprises a third waveguide and an optical coupler (second optical coupler) for coupling the light beam from the first waveguide to the third waveguide, wherein the third waveguide is configured to guide the light beam coupled from the first waveguide to a light beam shaping structure, wherein the light beam shaping structure is configured to propagate the light beam received from the third waveguide to the light emitting area such that the beam divergence of the light beam emitted from the light emitting area is lower than the beam divergence of the light beam received from the third waveguide, wherein the light beam guided by the second waveguide to the light beam shaping structure and the light beam guided by the third waveguide to the light beam shaping structure are optionally emitted from the light emitting area with substantially parallel central propagation axes (as defined by the beam centroids). Optionally, the central propagation axes can comprise a small angle and be aligned to illuminate a defined (e.g. adjacent) point within a certain distance.

[0039] Optionally, the optical device can comprise a substrate, wherein the first waveguide and the at least second waveguide are formed within the substrate. The substrate is optionally a transparent substrate, in particular a glass substrate. Advantageously, the substrate comprises a borosilicate glass, such as Corning (R) EAGLE XG (R), which is an alkaline earth boro-aluminosilicate glass type. The thickness of the substrate can be larger than 100 pm, optionally larger than 250 pm. The substrate is optionally in the form of a sheet or plate, and the thickness of the substrate (defined as the shortest dimension of the substrate) is lower than the dimensions of the substrate in the two directions perpendicular to the shortest dimension by a factor of optionally at least 10, further optionally at least 100, further optionally at least 1000. The thickness of the substrate is optionally less than 5 cm, further optionally less than 2 mm, further optionally less than 1 mm. Optionally, the first waveguide and the at least second waveguide are formed within the substrate by direct laser writing, in particular femtosecond direct laser writing. In this way, waveguides can be realized with low propagation losses. For example, experiments have shown a propagation loss of less than 0.4 dB / cm for blue light (wavelength of 450 nm). Advantageously, by direct laser writing the waveguides can be formed, a 3D waveguide track can be provided. Thus, the layers of the optical shaping elements, in particular mirrors, can be combined with the layers of the waveguides. Optionally, the first waveguide extends within the substrate substantially perpendicular to the thinnest dimension of the substrate. If the optical shaping structure comprises a polymer, the refractive index of the polymer should be equal to or similar to the refractive index of the substrate, for example a difference of less than 0.1. In this way, total internal reflection can be avoided. The optical shaping elements can be formed by the substrate and / or by external structures adjacent to the substrate, for example. Optionally, the second waveguide and / or the first waveguide emits single mode (Gaussian beam) light, in particular light with a high beam quality, wherein M 2 The metric is optionally less than 3, further optionally less than 2, further optionally less than 1.5. Thus, a small spot size can be achieved. Laboratory results have shown that a coupling between single mode waveguides can be achieved with more than 95%. Optionally, the light emitting area is provided by a surface of the substrate.

[0040] Generally, a method for direct laser writing of a waveguide in a substrate optionally comprises the following steps:

[0041] - using a tightly focused laser beam (with e.g. a width of 1 pm) and moving the substrate to create the structure.

[0042] If the optical device is to be used with a high power external light source of near ultraviolet light (UV), as can be used with the optical devices disclosed herein, femtosecond direct laser writing (also referred to as femtosecond laser direct writing or FDLW) can be employed. The FDLW optionally comprises one or more of the following steps:

[0043] - providing a substrate comprising a transparent dielectric material and / or comprising a glass, a ceramic, a polymer and / or a crystalline material;

[0044] - multiphoton (i.e. more than 2 photons) absorption using photons with energy lower than the bandgap of the substrate material, and / or wherein the pulses are low-to-mid frequency femtosecond pulses, e.g. between 20 kHz and 10 MHz, optionally between 80 kHz and 5 MHz, in particular between 100 kHz and 2 MHz, even more in particular between 500 kHz and 1.5 MHz, and / or wherein the pulses have a medium pulse width, e.g. between 40 fs and 2 ps, optionally between 100 fs and 1 ps, in particular between 200 fs and 400 fs.

[0045] Another laser writing technique is 2PP (2-photon polymerization) laser writing, which can include two-photon lithography or multi-photon lithography. In comparison to femtosecond direct laser writing, it can include one or more of the following steps or characteristics:

[0046] - use of femtosecond pulses with typically high frequency, e.g. 80 MHz, low pulse width < 100 fs;

[0047] - two-photon absorption is a third order process for the third order susceptibility, a second order process for the light intensity;

[0048] - provision of a special resist (photosensitive material) which is highly transparent for photons of wavelength l, but has a high absorption for photons of wavelength l / 2.

[0049] The present disclosure also relates to a backlight unit comprising an optical device as disclosed herein and comprising a light source coupled to the first waveguide. With the present disclosure, light from one light source can be distributed to many pixels (e.g. more than 1000 pixels), in particular while maintaining single mode quality. In particular, it allows to allocate and provide one collimated light beam for each sub-pixel of a display to be illuminated. That is, a 2D grid of light beams perpendicular to the backlight surface can be achieved, with a pitch between adjacent light beams in one direction e.g. between 30 pm and 500 pm. This corresponds to a typical sub-pixel pitch of a display. The light source is optionally a laser, in particular a single mode laser diode. The light source is optionally of low M 2a metric, e.g. less than 3, further optionally less than 2, further optionally less than 1.5. Thus, a moderate to high coupling efficiency to the (in particular single mode) waveguide can be achieved. The laser is optionally an edge emitting and / or vertical cavity emitting laser diode. The coupling of the light beam emitted from the light source to the first waveguide can also be indirect, i.e. through another waveguide or waveguide cascade. The coupling of the light beam emitted from the light source to the waveguide is optionally achieved using a microlens and / or butt coupling. Laboratory results show that the coupling efficiency exceeds 50%. Optionally, the light source is configured to emit light with a center wavelength between 300 nm and 470 nm, e.g. 450 nm or 405 nm. Optionally, the backlight unit comprises more than one light source. If multiple light sources are used, each illuminating a certain portion of the area, local dimming of the area to be illuminated can be achieved to increase the contrast (or equivalently, the contrast ratio). Furthermore, a full color option with center wavelengths of 460 nm, 530 nm and 630 nm for the laser diodes is possible.

[0050] The present disclosure further relates to display panels (or "displays"). Currently available displays have some drawbacks.

[0051] One problem relates to the color gamut of LCDs.

[0052] The human eye has three different types of "pixels" that can sample the spectrum of light that is incident on it. Depending on the spectral composition of the light that is incident on the eye, different "colors" are perceived. This fact is very useful for displays, as they only need to emit three different wavelengths of light to "simulate" all colors. A perfect display would be able to spectrally process each "pixel" of the eye separately. This can be done by using, for example, a blue laser beam of 400 nm, a red laser beam of 700 nm, and a green laser beam of typically 530 nm.

[0053] LCDs used so far do not use laser diodes, but in most cases LEDs with a yellow phosphor on top of them, which results in a continuous spectral emission over the whole visible spectral range. Color filters are then used to "cut out" the blue, green and red parts of that spectrum. This results in a very broad spectrum for each color, which means that, for example, a red sub-pixel also emits a significant amount of "green" light, which is called color cross-talk. Color cross-talk limits the range of colors that can be displayed, e.g. there is no pure red, only a yellowish red.

[0054] Quantum dots solve this problem by doing it better than yellow phosphor: they absorb blue light and emit it at a different peak at the desired wavelength. Still not as sharp as a laser, but with a spectral width of e.g. 30 nm already much better than phosphor. So far, quantum dots are used in backlights of TVs sold under the QLED brand by e.g. Samsung (R). In such a backlight, the blue LEDs emit light which is distributed over the entire display array before it hits a thin film of quantum dots ("quantum dot enhancement film" or QDEF). In the film, red and green quantum dots absorb part of the blue light and convert it to red and green light, - together with the blue LEDs - forming a mix of RGB light throughout the film plate. Then, the color filters only select the light of that filter color for the respective sub-pixel and reflect the rest.

[0055] Another problem is the optical efficiency of LCDs.

[0056] To generate e.g. red light for a red sub-pixel, a color filter must be used to block all non-red light, which means that for a standard white backlight at least 66% of the light is lost. Typically, the loss is much higher because the spectrum of the light does not match the transmission spectrum of the filter very well. Before entering the liquid crystal structure, an additional filter must be used to polarize the light, introducing another loss of about 30%. Finally, the black borders separating the sub-pixels absorb about 33% of the light. Taking all these factors into account, typically more than 90% of the light generated in a backlight is lost and never reaches the viewer, resulting in high power consumption and heat in the display relative to the brightness achieved by the display.

[0057] By using QDEF in an LCD, the efficiency is only slightly improved over a standard LED-based LCD, because the main losses related to 3 separate color filters, polarization and the black borders of the liquid crystal grid are still present. It should be noted that the energy efficiency of OLED displays, the second major technology used today, is roughly comparable to the current LCD technology.

[0058] In recent years, a more efficient way of using quantum dots in an LCD than QDEF has been proposed: positioning the quantum dots behind the "shutter" part of the LCD to act as a replacement for the specific color converters and color filters. This approach is called Quantum Dot Color Filter Replacement (QDCFR). For this, only green quantum dots are positioned at the green sub-pixel locations, and the same for red. This way, a blue backlight emits blue light which passes the "shutter" without the need for color filtering, meaning that the light loss is significantly reduced.

[0059] The advantages of QDCFR over QDEF are:

[0060] - higher energy efficiency because no color filters are used in the LCD;

[0061] - very good viewing angle and identical contrast ratio at all viewing angles due to uniform scattering angle of QDs;

[0062] - only one LCD cell type (blue);

[0063] - lower price and possibly enhanced contrast ratio;

[0064] - blue LC cells usually also have the fastest switching time.

[0065] Nonetheless, QDCFR suffers from at least two conceptual design problems with respect to the backlight unit.

[0066] One problem is sub-pixel cross-talk.

[0067] Light rays for e.g. the green sub-pixel that pass through the "shutter" should only hit the quantum dots of this sub-pixel. This is difficult to achieve if the propagation distance between the shutter and the quantum dots is large and the angle of the light rays is large. In a typical display stack, the distance between the liquid crystal cell and the quantum dots is about 700 pm. Even for a collimated backlight with a cone opening half-angle of only 10° (which is not available on the market and would likely result in a large additional optical loss), sub-pixel cross-talk is usually unavoidable. The only possible solutions are to make very large pixels (which is undesirable), to reduce the aperture size of the liquid crystal (which results in a large drop in energy efficiency), or to use a highly collimated (e.g. beam divergence angle of less than 1°) backlight (such a backlight has not been realized so far).

[0068] Alternatively, the display stack can also be changed by moving the top polarizer inside the liquid crystal cell ("in-cell" polarizer) and the quantum dots can be placed in the position of the color filter in a standard layout, i.e. the position of the liquid crystal. In this layout, sub-pixel cross-talk can be sufficiently suppressed. The problem with this approach is that it is very difficult to manufacture functional in-cell polarizers and mass market producible products with them have not been released yet.

[0069] The other problem of QDCFR is the reduced contrast ratio, which cannot be overcome by using in-cell polarizers either.

[0070] Even if a high contrast ratio in-cell polarizer is available, the contrast ratio of a QDCFR display can be significantly lower than a standard LCD display. The reason for this is that since the quantum dots are uniform scatterers in 360° angular directions, light rays that propagate through the LCD at an oblique angle will be converted to new light rays at random angles, some of which are normal angle. This means that if the display is viewed at normal angle, light rays that were at oblique angles (before hitting the QDCFR) can now also be seen, which show a poor contrast ratio and are typically only seen when the display is viewed at an angle (when using QDEF or standard LED-BLU).

[0071] Thus, while the quantum dots provide the same contrast ratio at all viewing angles, due to the fact that they are uniform scatterers, the contrast ratio of a QDCFR LCD is averaged over all viewing angles. This reduces the contrast ratio when viewed at normal angle from 1 :3000 to 1 :130 (see e.g.: Han, S., Kiselev, F.D., and Mlejnek, M. (2019), 75-2: Quantum Dots on Color Filter LCD Design Study. SID Symposium Digest of Technical Papers, 50: 1067-1070.).

[0072] It is another object of the present disclosure to address or alleviate at least some of the problems of prior art displays. In particular, it is an object of the present invention to provide a display that is more efficient, has a better color gamut and / or a higher contrast ratio and / or a better viewing angle.

[0073] A display panel comprising a backlight unit as described in the present disclosure is proposed. Such a display can enable illumination with collimated light, mitigating one or more of the above-mentioned problems. In particular in a QDCFR, the sub-pixel cross-talk problem can be solved and no intra-cell polarizer is needed to avoid sub-pixel cross-talk (although an intra-cell polarizer can of course still be used, e.g. to make the display stack more compact). Furthermore, in a QDCFR, the problem of reduced contrast ratio is also solved, as only the normally angled light rays pass through the liquid crystal cell and the maximum contrast ratio is achieved. However, the advantages are not limited to QDCFR displays. In general, the efficiency of the backlight display can be improved. The efficiency of a conventional display can be further improved due to the total internal reflection at the cover material of the display panel (e.g. glass), which can be avoided, resulting in a low output extraction efficiency (see e.g.: Han, S., Kiselev, F.D., and Mlejnek, M. (2019), 75-2: Quantum Dots on Color Filter LCD Design Study. SID Symposium Digest of Technical Papers, 50: 1067-1070). With the present disclosure, the cover material can be exchanged with any other polymer.

[0074] Furthermore, the present disclosure allows to achieve a small beam diameter. This ensures that no light is shot into the black borders that usually separate the sub-pixels, which means that a loss of 30-50% can be avoided. This results in a strong increase of the transmission.

[0075] To increase the contrast ratio by local dimming, two LC layers can be stacked together. Also, the transmission can be increased, as no light is shot into the borders. Furthermore, the Moire problem that can occur due to the misalignment of two grids in case the LC grids are stacked together can be solved. As the beam can be made much smaller than the aperture of each individual sub-pixel, there is enough lateral alignment tolerance (e.g. +- 20 pm) between the two LCDs.

[0076] Furthermore, for QD displays, the material usage of quantum dots can be reduced, as a spot size of less than 20 pm by 20 pm can be achieved at the location of the quantum dots. For current TVs, the sub-pixel size can be 300 x 100 pm, which is usually uniformly covered by the quantum dots. Covering only a 20 x 20 pm area instead of a 300 x 100 pm area can save about 98.7% of the quantum dot material. Potentially, this reduction can even allow the use of cadmium (Cd) based quantum dots, despite the strict RoHS requirements. Cd quantum dots have better performance than indium phosphide quantum dots, but the latter are not restricted by RoHS.

[0077] The display panel is optionally a flat panel display. Optionally, the display panel is a liquid crystal display, further optionally a quantum dot display. Optionally, the light beams from the second waveguide that are emitted from the beam shaping structure impinge on one sub-pixel, and / or a liquid crystal (LC) area associated with one sub-pixel, and / or a quantum dot area associated with one sub-pixel. Optionally, further waveguides of the second waveguide type are each associated with one sub-pixel, wherein the associated sub-pixel is different for different waveguides.

[0078] The display panel optionally comprises one or more of:

[0079] - a first polarizer,

[0080] - a TFT (thin film transistor) glass,

[0081] - a cover glass,

[0082] - a second polarizer (often referred to as "analyzer") and / or an intra-cell polarizer,

[0083] - a layer containing light conversion structures (see below),

[0084] - a color filter for blocking pump light and reflecting ambient light, which can cause undesired excitation of the light conversion structures,

[0085] - a glass layer protection.

[0086] In an optional embodiment, the display panel comprises at least a first type of light conversion structure, said first type of light conversion structure optionally comprising a first type of quantum dots or quantum rods for converting light beams emitted by the light source into a first color range, wherein the beam shaping structure is configured such that light beams guided from the second waveguide to the beam shaping structure and emitted from the light emitting area impinge on the first type of light conversion structure, which is associated with a first color sub-pixel of the display panel. Optionally, the first type of light conversion structure comprises a phosphor. In particular, the light source provides pump light beams for this light conversion structure.

[0087] Optionally, the display panel comprises at least a second type of light converting structure, optionally comprising a second type of quantum dots or quantum rods, for converting a light beam emitted from the external light source to a second color range different from the first color range, wherein the light beam shaping structure is configured such that a light beam guided from the third waveguide to the light beam shaping structure and emitted from the light emitting area impinges on the second type of light converting structure, which is associated with a second color sub-pixel of the display panel, wherein the second color sub-pixel is optionally adjacent to the first color sub-pixel. Thus, in practice, the first color sub-pixel and the second color sub-pixel can display different colors. Optionally, two, three, four or more (color) sub-pixels can form one pixel.

[0088] Typically, no blue QDs are used in QDCFRs. Instead, a blue LED, e.g. of 450 nm, is used to pump the red and green QDs and to provide blue light. In this case, typically some transparent scattering structures are used to diffuse the blue light and to ensure that there is no angle-dependent color shift. Such a setup can also be used in the current disclosure. However, due to the coherence of the light beam, this can lead to speckle. Therefore, it is advantageous to use a lens or a diffractive optical element to diffuse the light beam (not impinging on the QDs). Alternatively and optionally, a third type of light converting structure (optionally quantum dots or quantum rods) is also used as a diffuser, and the pump wavelength is set to be sufficiently short (even UV) compared to the emission wavelength of the third type of light converting structure. Optionally, the display panel comprises at least a third type of light converting structure, optionally comprising a third type of quantum dots or quantum rods, for converting a light beam emitted from the external light source to a third color range different from the first color range and the second color range, the external light source being configured to emit a light beam with a center wavelength shorter than the center wavelength of the first color range, the second color range and the third color range. Optionally, the light source emits light in the ultraviolet (UV) spectrum (e.g. 400 nm or less). Since the human eye has 1 / 100 sensitivity at 400 nm compared to 450 nm, the filter blocking the “pump” light can be omitted, thus simplifying the display stack. Moreover, some quantum dots have a significantly higher absorption in the UV than at 450 nm.

[0089] The first and / or second and / or third color range can each be, for example, one of the following ranges:

[0090] - between 380 and 495 nm; or

[0091] - between 495 and 580 nm; or

[0092] - between 580 and 800 nm.

[0093] The first and second and third color ranges are optionally non-overlapping. The first and / or second and / or third color range can each for example have a center wavelength that is one of:

[0094] - 400 nm; or

[0095] - 530 nm; or

[0096] - 700 nm.

[0097] Optionally, the display panel comprises a fourth type of light converting structure, which fourth type of light converting structure optionally comprises a fourth type of quantum dots or quantum rods, for converting a light beam emitted from the external light source to a fourth color range that is different from the first color range, the second color range and the third color range.

[0098] Optionally, the light converting structure associated with the first color sub-pixel and the light converting structure associated with the second color sub-pixel are separated by a boundary comprising a material that is substantially opaque to at least the center wavelength of the first color range and / or the center wavelength of the second color range. Thus, cross-excitation between the light converting structures associated with different sub-pixels can be prevented. Optionally, the boundary blocks at least 90% of the intensity of light having the center wavelength of the first color range and the center wavelength of the second color range.

[0099] Optionally, the optical arrangement comprises at least a further waveguide and a further optical coupler for coupling a light beam from the first waveguide to the further waveguide,

[0100] wherein the further waveguide directs a light beam emitted from the external light source to the light beam shaping structure, and the light beam shaping structure is further configured such that a light beam emitted from the light emitting area has a lower light beam divergence than a light beam directed by the further waveguide to the light beam shaping structure,

[0101] wherein the light beam shaping structure is configured such that a light beam directed from the further waveguide to the light beam shaping structure and emitted from the light emitting area impinges on an optical diffusion element associated with the third color sub-pixel of the display panel. In this embodiment, one of the colors displayed by the display panel can optionally be the color emitted by the light source. Due to the optical diffusion element, the viewing angle can be improved.

[0102] Optionally, the light conversion structure associated with the first color sub-pixel and the light conversion structure associated with the second color sub-pixel are provided in a light conversion layer, wherein a light filter layer, in particular a short pass light filter layer, is provided, wherein a light beam emitted from the light emitting area passes the light filter layer before reaching the light conversion layer, wherein the light filter layer has a higher reflectivity for a central wavelength of a light beam emitted by the external light source than for a central wavelength of the first color range and optionally also of the second color range. Thus, the pump light from the light source can be transmitted to the light conversion structure, but the light emitted from the light conversion structure can be reflected. Thus, the efficiency is improved. BRIEF DESCRIPTION OF DRAWINGS

[0103] For example, the disclosure will be further explained with respect to some selected embodiments shown in the drawings. These embodiments should not be considered as limiting the disclosure, however.

[0104] Figure 1 A cross-sectional view of a prior art QDCFR display is schematically shown.

[0105] Figure 2 A detailed cross-sectional view of a prior art QDCFR display is schematically shown.

[0106] Figure 3 A cross-sectional view of a display panel according to the disclosure is schematically shown.

[0107] Figure 4 A top view of a backlight unit of a display panel of Figure 3 is schematically shown.

[0108] Figure 5 A cross-sectional view of a display panel with in-cell polarizer according to the disclosure is schematically shown.

[0109] Figure 6 A cross-sectional view of a display panel according to the disclosure is schematically shown and advantages over a prior art display according to Figure 1 are explained.

[0110] Figure 7 An X-Z plane of a Zemax(R) simulation is shown, demonstrating a reduction of the divergence angle.

[0111] Figure 8 A Y-Z plane of the same simulation as Figure 7 is shown.

[0112] Figure 9 An X-Z plane of another Zemax(R) simulation is shown, wherein several waveguides of the second waveguide type illuminate the same optical shaping element.

[0113] Figure 10 A Y-Z plane of the same simulation asFigure 9 The same simulated YZ plane.

[0114] Figure 11 It shows the relationship with Figure 9 The same simulated XY plane. Detailed Implementation

[0115] Figure 1 The diagram illustrates layers and a light beam in a prior art display panel 160, which is a QDCFR display with a standard polarizer layer. The display panel 160 includes a backlight unit 130 with a brightness enhancement film 132. The backlight unit 130 emits a light beam with a half-angle of approximately 10°. Subsequently, a first polarizer 161 and a TFT glass 162 with an LC unit layer 163 on top are provided. The light beam passing through a single LC unit is shown on the right side of the LC layer 163. Before illuminating a layer 173 of the display panel 160 having quantum dots for different colors and color sub-pixels, the light beam passes through a cover glass 164, a second polarizer 165, and a low-pass filter 166 (used to reflect QD light but allow pump light to pass through). As can be seen from the light beam exiting the single LC unit, the beam reaches multiple sub-pixels, resulting in sub-pixel crosstalk and reduced contrast ratio.

[0116] Figure 2 The details of a prior art QDCFR display 160 are schematically shown, illustrating a problem that cannot be overcome in prior art displays even when using an intra-cell polarizer. The intra-cell polarizer 165a is in the same layer as the liquid crystal layer 163 (or more precisely, adjacent to the LC cell) and the quantum dot-containing layer 173. They are sandwiched between two glass layers 162 and 164. Light rays from the backlight are shown as arrow 180. If the quantum dots are used to uniformly scatter these rays in all directions (i.e., in the QDCFR case), the light rays come from the backlight at an angle and produce a non-ideal contrast ratio at the display output. This is due to the different path lengths of the light rays passing through the liquid crystal 163 and the birefringence axis of the liquid crystal cell as seen by the light rays at the angle of inclination compared to the light rays at the normal angle. Therefore, the contrast ratio is reduced when viewing the display 160 at the normal angle.

[0117] Figure 3A display panel 60 according to the present disclosure is shown. The display panel 60 comprises a backlight unit 30. The backlight unit 30 comprises an optical device 1 for controlling light. The optical device 1 comprises a first waveguide 2 for receiving a light beam from an external light source. In this case, the external light source is provided by a light source 31 of the backlight unit 30. The light source 31 is for example a laser diode. The first waveguide 2 is connected to a second waveguide 3 by an optical coupler 4 for coupling the light beam from the first waveguide 2 to the second waveguide 3. The optical device 1 comprises a beam shaping structure 5 having a light emitting area 6 for emitting the light beam. The second waveguide 3 is configured to guide the light beam coupled from the first waveguide 2 to the beam shaping structure 5. The beam shaping structure 5 is configured to propagate the light beam received from the second waveguide 3 to the light emitting area 6 such that the beam divergence of the light beam emitted from the light emitting area 6 is lower than the beam divergence of the light beam received from the second waveguide 3. In particular, the beam divergence angle is smaller.

[0118] The beam shaping structure 5 comprises an optical shaping element 7. The second waveguide 3 guides the light beam coupled from the first waveguide 2 to the optical shaping element 7. In this embodiment, the optical shaping element 7 is a concave mirror. The optical shaping element 7 is provided by a polymer structure 8. Optionally, the optical shaping element 7 is created by UV nanoimprinting in the polymer structure 8.

[0119] Furthermore, the optical device 1 comprises a third waveguide 9 and an optical coupler 10 for coupling the light beam from the first waveguide 2 to the third waveguide 9. The third waveguide 9 is configured to guide the light beam coupled from the first waveguide 2 to the beam shaping structure 5, wherein the beam shaping structure 5 is configured to propagate the light beam received from the third waveguide 9 to the light emitting area 6 such that the beam divergence of the light beam emitted from the light emitting area 6 is lower than the beam divergence of the light beam received from the third waveguide 9. The light beam guided by the second waveguide 3 to the beam shaping structure 5 and the light beam guided by the third waveguide 9 to the beam shaping structure 5 are emitted from the light emitting area 6 with substantially parallel central propagation axes. Similar to the second waveguide 3 and the third waveguide 9, the optical device 1 comprises further waveguides.

[0120] The optical device 1 comprises a substrate 11. The first waveguide 2, the second waveguide 3 and the third waveguide 9 are formed within the substrate 11. The substrate 11 can be considered as a backlight glass.

[0121] Figure 4This is a top view of the backlight unit 30. The figure illustrates how fan-out to a 2D grid is achieved. A primary fan-out waveguide 12 is provided. Light is coupled from the primary fan-out waveguide 12 to four secondary fan-out waveguides 13 via optical couplers. Each of the primary fan-out waveguide 12 and the secondary fan-out waveguides 13 can form a first waveguide 2 as understood in this disclosure. From each of the primary and secondary fan-out waveguides 12, 13, an optical coupler can couple the light output to second and third waveguides 3, 9, and other waveguides of their type, which guide the light to the beam shaping structure 5 (see [reference]). Figure 3 Of course, only some of the primary and / or secondary fan-out waveguides 12, 13 can be used as the first waveguide 2. In this way, a 2D grid of collimated beams can be emitted from the front surface of the backlight unit 30. The emitted beams are optionally parallel or nearly parallel to each other. Furthermore, the backlight unit 30 may include additional light sources 31, which provide an additional fan-out layout as described above. Thus, multiple light sources can each provide a 2D sub-grid of collimated beams, together covering a larger area. Therefore, a backlight unit 30 emitting a grid of collimated beams is realized using one or more light sources 31.

[0122] Again from Figure 3 As can be seen, the display panel 60 includes a first polarizer 61 through which the light beam emitted from the backlight unit 30 passes. Subsequently, a TFT glass 62 may be provided. The light beam then passes through a liquid crystal layer 63, followed by a TFT cover glass 64. Typically, any LCD stack, as known in the art, can be provided for the display panel 60. This is followed by a second polarizer 65 and a light filter layer 66, which will be explained in more detail below.

[0123] The display panel 60 includes at least a first type of light conversion structure 67 for converting a light beam emitted from the light source 31 to a first color range, wherein the beam shaping structure 5 is configured such that a light beam guided from the second waveguide 3 to the beam shaping structure 5 and emitted from the light-emitting region 6 illuminates the first type of light conversion structure 67. The light conversion structure 67 is associated with a first color sub-pixel 68 of the display panel 60. The relative positions of the color sub-pixel 68 and other color sub-pixels mentioned below are also... Figure 4 The text is a schematic instruction.

[0124] The display panel 60 also includes a second type of light conversion structure 69 for converting a light beam emitted from the external light source 31 to a second color range different from the first color range. The beam shaping structure 5 is configured such that a light beam guided from the third waveguide 9 to the beam shaping structure 5 and emitted from the light-emitting region 6 illuminates the second type of light conversion structure 69. The light conversion structure 69 is associated with a second color sub-pixel 70 of the display panel 60. Figure 3 and Figure 4It can be seen that the second color sub-pixel 70 is adjacent to the first color sub-pixel 68.

[0125] The display panel 60 comprises a third type of light conversion structure 71 for converting light beams emitted from the external light source 31 to a third color range different from the first color range and the second color range. The light source 31 is configured to emit light beams with a center wavelength shorter than the center wavelengths of the first color range, the second color range and the third color range. For example, the light source 31 can emit UV light. Thus, light that passes through the light conversion structures 67, 69, 71 without conversion does not degrade the quality of the picture displayed by the display panel 60. The pump wavelength of the light conversion structures 67, 69, 71 is suitable for the light emitted by the light source 31.

[0126] In this embodiment, the first type, the second type and the third type of light conversion structure 67, 69, 71 comprise first type, second type or third type of quantum dots, respectively. Of course, other embodiments of the light conversion structures 67, 69, 71 are possible.

[0127] The light conversion structure 67 associated with the first color sub-pixel 68 and the light conversion structure 69 associated with the second color sub-pixel 70 are separated by a border 72 comprising a material substantially opaque to at least the center wavelength of the first color range and the center wavelength of the second color range. Thus, cross-excitation between the light conversion structures 67, 69 associated with the first color sub-pixel 68 and the second color sub-pixel 70 can be prevented.

[0128] The light conversion structure 67 associated with the first color sub-pixel 68 and the light conversion structure 69 associated with the second color sub-pixel 70 are provided in a light conversion layer 73. The light conversion layer 73 is adjacent to the light filter layer 66. Light beams emitted from the light emitting area 6 pass through the light filter layer 66 before reaching the light conversion layer 73. The light filter layer 66 has a lower reflectivity for the center wavelength of the light beams the light source 31 is configured to emit than for the center wavelengths of the first color range and the second color range. Thus, light from the light source 31 can pass through the light filter layer 66 to the light conversion layer 73, while light emitted backwards from the light conversion structures 67, 69 is reflected to the front surface of the display panel 60, i.e. in the direction of the viewer. On top of the light conversion layer 73, the display panel 60 comprises a color filter layer 74. The color filter layer 74 blocks unconverted light from the light source 31 from being emitted from the display panel 60 and reflects ambient light that would otherwise cause unwanted excitation of the light conversion structures 67, 69, 71. A glass layer 75 is provided on top of the color filter layer 74 to protect the underlying structures.

[0129] Figure 5 The illustrated embodiment of the display panel 60 is similar to the one illustrated in Figure 3 with the backlight unit 30 being replaced by the light source 31. Figure 3The same applies to the display unit 60. The display unit 60 includes a first polarizer 61 and a TFT glass 62. However, a second polarizer 65a is provided as an in-unit polarizer, as part of the LC layer 63 (or more precisely: adjacent to the LC unit). Furthermore, light conversion structures 67, 69, and 71 are also disposed within the unit along with the LC layer 63. This has the advantage of enabling a more compact design. A TFT cover glass 64 is disposed on top of the LC layer 63.

[0130] Figure 6 A side view of the display panel 60 according to this disclosure is schematically shown, and an illustration is provided relative to... Figure 1 The advantages of the prior art display 160 shown are illustrated. The display panel 60 includes a backlight unit 30, wherein a light source and a first waveguide are not shown. Subsequently, a first polarizer 61 and a TFT glass 62 are provided, wherein an LC cell layer 63 (which is in Figure 6 (The right-hand side of the TFT glass in the diagram is shown) on top of the TFT glass 62. A light beam emitted from the optical shaping element 7 of the beam shaping structure 5 is shown, passing through a single LC cell of layer 63. Before illuminating layer 73 of the display panel 60, which has quantum dots for different colors and color sub-pixels, the beam passes through cover glass 64, a second polarizer 65, and a low-pass filter 66 (used to reflect QD light but allow pump light to pass through). It can be seen that, due to the reduced divergence angle through the beam shaping structure 5 (only the optical shaping element 7 of the beam shaping structure 5 is shown), the beam passing through one LC cell illuminates only the quantum dot associated with one sub-pixel. Therefore, there is no sub-pixel crosstalk and contrast ratio reduction. At the top, a glass layer 75 is provided.

[0131] Figure 7 and Figure 8 The Zemax(R) simulation is shown, where Figure 7 The XZ plane is shown. Figure 8A Y-Z plane is shown. For this simulation, it is assumed that the second waveguide 3 (not visible) is bent towards the optical shaping element 7 at an angle of 12°. The waveguide is arranged in a substrate 11, with the beam shaping structure 5 of the optical shaping element 7 arranged in contact with the substrate 11. The end of the second waveguide 2 is at 10 pm above the interface of the substrate 11 and the beam shaping structure 5, from which the second waveguide 2 emits a light cone with an opening half-angle of 3.5°. The optical shaping element 7 is arranged as a concave mirror with a bending radius of 0.32 mm and 0.65 mm in different axes orthogonal to each other. The shown light beams pass through the cells of the LC layer 63 and are substantially focused on a first type of light conversion structure 67 associated with a first color sub-pixel 68. The light conversion structure 67 is arranged in a light conversion layer 73. The simulation shows that a spot size of 4 pm by 10 pm of the light beams at the light conversion layer 73 is achievable. The pixel pitch of this simulation is 220 pm, with the LCD sub-pixel aperture arranged as 58 pm by 58 pm and the QD layer pixel aperture arranged as 220 pm by 73 pm.

[0132] Figures 9 to 11 Another Zemax(R) simulation is shown, in which Figure 9 An X-Z plane is shown, Figure 10 A Y-Z plane is shown, Figure 11 An X-Y plane is shown. Here, three waveguides of the second waveguide 3 type (not shown) illuminate the same optical shaping element 7 and the resulting light beams are shown. The parameters are essentially the same as in Figure 7 and Figure 8 the simulations shown. In particular, the end angle of each waveguide is the same as in the waveguides in Figure 7 . That is, the three waveguides have the same angle and lie in the same tilted plane, parallel to each other. However, the spacing of the waveguides from the light shaping element 7 is varied to 14 pm, with the spacing of the middle waveguide from each of the two neighboring waveguides being 14 pm for both cases. This design is adapted for a 75 pm pixel pitch, i.e. a 25 pm sub-pixel pitch. Again, the optical shaping element 7 is provided as a concave mirror, and the bending radii of this mirror are 0.3 mm for the x-direction and 0.48 mm for the y-direction. The mirror has an angle of 37.6° with respect to the extension plane of the liquid crystal (LC) layer 63 and / or the light conversion layer 73, more generally, with respect to the display surface of the display panel 60. As can be seen from this figure, the light beams emitted from each of the three waveguides are guided by the optical shaping element 7 to one of three neighboring cells of the LC layer 63 and one of three neighboring light conversion structures in the light conversion layer 73, each light conversion structure being associated with a different color sub-pixel. Thus, an easier setup can be achieved.

Claims

1. Optical device (1) for controlling light, the optical device (1) comprising: a first waveguide (2) for receiving a light beam from an external light source, at least a second waveguide (3), an optical coupler (4) for coupling a light beam from the first waveguide (2) to the second waveguide (3), a beam shaping structure (5) having a light emitting area (6) for emitting a light beam, wherein the second waveguide (3) is configured to guide a light beam coupled from the first waveguide (2) to the beam shaping structure (5), wherein the optical device (1) comprises a substrate (11), characterized in that the beam shaping structure (5) is configured to propagate a light beam received from the second waveguide (3) to the light emitting area (6) such that a beam divergence of the light beam emitted from the light emitting area (6) is lower than a beam divergence of the light beam received from the second waveguide (3), wherein the first waveguide (2) and at least the second waveguide (3) are formed within the substrate (11) by direct laser writing.

2. The optical device (1) according to claim 1, characterized in that the beam shaping structure (5) comprises an optical shaping element (7), wherein the at least second waveguide (3) guides a light beam coupled from the first waveguide (2) at the optical shaping element (7).

3. The optical device (1) according to claim 2, characterized in that the optical shaping element (7) is a concave mirror or a diffractive optical element.

4. The optical device (1) according to claim 3, characterized in that the optical shaping element (7) has at least a first axis and a second axis, wherein a focal length of the optical shaping element (7) for the first axis is different from a focal length for the second axis.

5. The optical device (1) according to any one of claims 2 to 4, characterized in that the optical shaping element (7) is provided by a polymer structure (8).

6. The optical device (1) according to claim 5, characterized in that the polymer structure (8) is a UV nanoimprinted polymer structure.

7. The optical device (1) according to claim 5, characterized in that the optical shaping element (7) comprises a reflective coating.

8. The optical device (1) according to any one of claims 1 to 4, characterized in that the optical device (1) comprises a third waveguide (9) and an optical coupler (10) for coupling a light beam from the first waveguide (2) to the third waveguide (9), wherein the third waveguide (9) is configured to guide a light beam coupled from the first waveguide (2) to the beam shaping structure (5), wherein the beam shaping structure (5) is configured to propagate a light beam received from the third waveguide (9) to the light emitting area (6) such that a beam divergence of the light beam emitted from the light emitting area (6) is lower than a beam divergence of the light beam received from the third waveguide (9), wherein the light beam guided by the second waveguide (3) to the beam shaping structure (5) and the light beam guided by the third waveguide (9) to the beam shaping structure (5) are emitted from the light emitting area (6) with substantially parallel central propagation axes.

9. The optical device (1) according to any of the preceding claims 1-4, characterized in that the first waveguide (2) and at least the second waveguide (3) are formed by femtosecond direct laser writing.

10. A backlight unit characterized by The optical device (1) according to any one of claims 1 to 7 and 9 and comprising a light source (31) coupled to the first waveguide (2).

11. The backlight unit of claim 10, wherein, the light source (31) is a laser. the light source (31) is a laser.

12. The backlight unit according to claim 10 or 11, characterized in that, The optical arrangement (1) comprises a third waveguide (9) and an optical coupler (10) for coupling a light beam from the first waveguide (2) to the third waveguide (9), wherein the third waveguide (9) is configured to guide a light beam coupled from the first waveguide (2) to the beam shaping structure (5), wherein the beam shaping structure (5) is configured to propagate a light beam received from the third waveguide (9) to the light emitting area (6) such that a beam divergence of a light beam emitted from the light emitting area (6) is lower than a beam divergence of a light beam received from the third waveguide (9), wherein the light beam guided by the second waveguide (3) to the beam shaping structure (5) and the light beam guided by the third waveguide (9) to the beam shaping structure (5) are emitted from the light emitting area (6) with substantially parallel central propagation axes.

13. A display panel (60) characterized by The backlight unit (30) according to claim 10 or 11.

14. The display panel (60) according to claim 13, characterized by The display panel (60) comprises at least a first type of light conversion structure (67) for converting a light beam emitted from the light source (31) to a first color range, wherein the beam shaping structure (5) is configured such that a light beam guided from the second waveguide (3) to the beam shaping structure (5) and emitted from the light emitting area (6) impinges on the first type of light conversion structure (67) associated with a first color sub-pixel (68) of the display panel (60).

15. The display panel (60) according to claim 14, characterized by The first type of light conversion structure (67) comprises a first type of quantum dots or quantum rods.

16. The display panel (60) according to claim 14 or 15, characterized by The optical arrangement (1) comprises a third waveguide (9) and an optical coupler (10) for coupling a light beam from the first waveguide (2) to the third waveguide (9), wherein the third waveguide (9) is configured to guide a light beam coupled from the first waveguide (2) to the beam shaping structure (5), wherein the beam shaping structure (5) is configured to propagate a light beam received from the third waveguide (9) to the light emitting area (6) such that a beam divergence of a light beam emitted from the light emitting area (6) is lower than a beam divergence of a light beam received from the third waveguide (9), wherein the light beam guided by the second waveguide (3) to the beam shaping structure (5) and the light beam guided by the third waveguide (9) to the beam shaping structure (5) are emitted from the light emitting area (6) with substantially parallel central propagation axes.

17. The display panel (60) according to claim 16, characterized by The display panel (60) comprises at least a second type of light conversion structure (69) for converting light beams emitted from the light source (31) to a second color range different from the first color range, wherein the light beam shaping structure (5) is configured such that light beams guided from the third waveguide (9) to the light beam shaping structure (5) and emitted from the light emitting area (6) impinge on the second type of light conversion structure (69) associated with a second color sub-pixel (70) of the display panel (60).

18. The display panel (60) according to claim 17, characterized by The second color sub-pixel (70) is adjacent to the first color sub-pixel (68).

19. The display panel (60) according to claim 17, characterized by The second type of light conversion structure (69) comprises a second type of quantum dots or quantum rods.

20. The display panel (60) according to claim 17, characterized by The display panel (60) comprises at least a third type of light conversion structure (71) for converting light beams emitted from the light source (31) to a third color range different from the first color range and the second color range, characterized in that the light source (31) is configured to emit light beams having a center wavelength shorter than the center wavelengths of the first color range, the second color range and the third color range.

21. The display panel (60) according to claim 20, characterized by The third type of light conversion structure (71) comprises a third type of quantum dots or quantum rods.

22. The display panel (60) according to claim 17, characterized by The light conversion structure (67) associated with the first color sub-pixel (68) and the light conversion structure (69) associated with the second color sub-pixel (70) are separated by a border (72) comprising a material substantially opaque to at least the center wavelength of the first color range and / or the center wavelength of the second color range.

23. The display panel (60) according to claim 17, characterized in that The optical device (1) comprises at least a further waveguide and a further light coupler for coupling light beams from the first waveguide (2) to the further waveguide, wherein the further waveguide guides light beams emitted from the light source (31) to the light beam shaping structure (5) and the light beam shaping structure (5) is further configured such that the beam divergence of light beams emitted from the light emitting area (6) is lower than the beam divergence of light beams guided by the further waveguide to the light beam shaping structure (5), wherein the light beam shaping structure (5) is configured such that light beams guided from the further waveguide to the light beam shaping structure (5) and emitted from the light emitting area (6) impinge on an optical diffusion element associated with a third color sub-pixel of the display panel (60).

24. The display panel (60) according to claim 17, characterized by The light conversion structure (67) associated with the first color sub-pixel (68) and the light conversion structure (69) associated with the second color sub-pixel (70) are arranged in a light conversion layer (73), wherein a light filter layer (66) is arranged, wherein a light beam emitted from the light emitting area (6) passes through the light filter layer (66) before reaching the light conversion layer (73), wherein the light filter layer (66) has a higher reflectivity for a center wavelength of a light beam emitted by the light source (31) than for a center wavelength of the first color range.

25. The display panel (60) according to claim 24, characterized by The light filter layer (66) is a short-pass filter layer.

26. The display panel (60) according to claim 24, characterized by The light filter layer (66) has a higher reflectivity for a center wavelength of a light beam emitted by the light source (31) than for a center wavelength of the second color range.

Images