Backlight device and associated image generation device, head-up display and manufacturing method

Abstract

The invention relates to a backlight device (10) comprising: - a light source (14) configured to emit a source beam; - a reflector (15) configured to reflect at least one portion of the source beam as a reflected beam; - an integrally-formed component (16) comprising, on a first face, a reflective polariser (17) and, on a second face opposite the first face, an optical diffuser (18), the component (16) being configured to receive and transmit at least one portion of the reflected beam, characterised in that the first face of the component (16) is positioned on the side of the light source (14). The invention also relates to an image generation device, a head-up display and a manufacturing method for a component (16) for a backlight device (10). Drawing_references_to_be_translated

Description

Description Title of the invention: Backlighting device, image generation device, head-up display and associated manufacturing method

[0001] The present invention relates generally to the field of displays.

[0002] It relates more specifically to a backlighting device, used for example in a head-up display for a motor vehicle, as well as an image generation device, a head-up display and an associated manufacturing process.

[0003] Typically, a head-up display projects a virtual image into the driver's field of vision. This allows the driver to view information about the vehicle's operation, the lane ahead, or other details without taking their eyes off the road. The virtual image, containing the displayed information, is visually superimposed onto the surrounding environment.

[0004] Generally, a so-called "head-up display" includes, inside a casing, an image generation device from which emerges a source light beam and an optical projection system adapted to project an image generated by the image generation device outwards, via the windshield for example, so as to form the virtual image previously mentioned.

[0005] Head-up displays for motor vehicles using a liquid crystal display (LCD) in their image generation device are often exposed to two types of thermal stresses that cause the screen to heat up: one of these stresses is related to the light source of the head-up display, and the other to the concentration of sunlight on the screen.

[0006] Preserving LCD screens, which are sensitive components, requires an assembly of the head-up display parts adapted to reduce this heating.

[0007] In this context, the present invention proposes a backlighting device comprising: - a light source configured to emit a source beam, - a reflector configured to reflect at least part of the source beam into a reflected beam, - a component formed in one piece comprising, on one face, a polarizer reflective and, on a second face opposite the first face, an optical diffuser, said component being configured to receive and transmit at least part of the reflected beam, characterized in that the first face of the component is placed on the side of the light source.

[0008] Positioning the first face of the component towards the light source improves light recycling within the backlighting device. Specifically, if a portion of the source beam lacks the polarization transmitted by the reflective polarizer, it is reflected back by the polarizer and can be reinterpreted by the reflector and reflected back towards the component. This enhances light transmission through the backlighting device.

[0009] In addition, when external light (e.g., sunlight) enters the head-up display as far as the component, it does not directly reach the reflective polarizer, thus preventing the appearance of stray light in an observer's field of vision.

[0010] In one embodiment, the optical diffuser is etched onto a transparent substrate that carries the reflective polarizer.

[0011] As explained below, the component may include a substrate with a first face bearing the reflective polarizer and a second face opposite the first face and in which the diffuser is formed by etching.

[0012] For example, the engraving is a laser engraving.

[0013] In one embodiment, the reflective polarizer is laminated onto the optical diffuser.

[0014] For example, the optical diffuser produces a Gaussian elliptical type light diffusion.

[0015] One aspect of the invention also relates to an image generation device comprising a backlighting device as described above, further comprising a liquid crystal display placed downstream of the reflector in the path of propagation of the light, the liquid crystal display comprising a liquid crystal matrix interposed between an upstream polarizer and a downstream polarizer, said upstream polarizer being capable of selectively transmitting a component of light having a given upstream polarization.

[0016] In one embodiment, the reflective polarizer is adapted to reflect a light component having a polarization orthogonal to said upstream polarization.

[0017] In one embodiment, the reflector has a principal axis parallel to a principal direction of the source beam and the component is orthogonal to the principal axis of the reflector.

[0018] In one embodiment, the liquid crystal display is inclined with respect to the main direction of the source beam and the component is positioned parallel to the liquid crystal display.

[0019] One aspect of the invention also relates to a head-up display comprising an image generation device as described above and further comprising an optical projection system capable of reflecting a light beam generated by the image generation device towards a partially transparent blade.

[0020] Finally, one aspect of the invention relates to a method for manufacturing a component for a backlighting device from a substrate having a reflective polarizer on a first face and having a second face opposite to the first face, comprising a step of forming an optical diffuser by etching in the second face of the substrate.

[0021] For example, the optical diffuser formation step is a laser engraving step.

[0022] Of course, the different features, variants and embodiments of the invention can be combined with each other in various ways as long as they are not incompatible or mutually exclusive.

[0023] Furthermore, various other features of the invention become apparent from the attached description made with reference to the drawings which illustrate non-limiting embodiments of the invention and where:

[0024] [Fig. 1] is a schematic view showing the integration of a head-up display according to the invention in a motor vehicle.

[0025] [Fig. 2] represents a first embodiment of a backlighting device according to the invention.

[0026] [Fig. 3] represents a substrate equipped with a reflective polarizer prior to a step of forming an optical diffuser by laser etching.

[0027] [Fig. 4] represents the substrate of figure 3 after a step of forming an optical diffuser by laser etching.

[0028] [Fig. 5] schematically represents the arrangement of certain components of an image generation device according to the invention.

[0029] [Fig. 6] represents a second embodiment of a backlighting device according to the invention.

[0030] It should be noted that in these figures the structural and / or functional elements common to the different variants may have the same references.

[0031] Figure 1 schematically represents the main elements of a head-up display 1, intended for example to equip a vehicle 2, in particular a motor vehicle.

[0032] The display 1 of Figure 1 is adapted to project a virtual image 3 into the field of vision of a driver 4 of the vehicle 2, so that the driver 4 can see this virtual image 3 and any information it may contain without having to take his eyes off the road.

[0033] For this purpose, the display 1 includes a partially transparent blade 5 placed in the field of vision of the driver 4, an image generation device 6 adapted to generate an image light beam 7 and an optical projection system 8 adapted to reflect, towards said partially transparent blade 5, the image light beam 7 generated by the image generation device 6 after passing through a transparent window 9. The light beam reflected towards the partially transparent blade 5 is partly reflected by the partially transparent blade 5 towards the driver 4 and thus produces the virtual image 3.

[0034] The partially transparent blade 5 is here confused with the windshield of vehicle 2. In other words, it is the windshield of vehicle 3 which has the function of partially transparent blade 5 for the head up display 1.

[0035] As can be seen in Figure 1, the image generation device 6 and the optical projection system 8 are here placed in a housing 22, one opening of which is closed by the transparent window 9 already mentioned.

[0036] A first embodiment of the image generation device 6 according to the invention is illustrated in Figure 2. The image generation device 6 comprises a backlighting device 10, a liquid crystal display 11 covering the backlighting device 10, a first heat sink 12 and a second heat sink 13.

[0037] The backlighting device 10 comprises a light source 14 of the LED matrix type, a reflector 15, and an optical component 16. The light source 14 is configured to emit a source beam diverging around a principal direction D. The reflector 15 receives at least a portion of the source beam and reflects at least a portion of it back towards the optical component 16. The reflected beam is collimated. The optical component 16 receives at least a portion of the reflected beam and transmits at least a portion of it as a diffused beam towards the liquid crystal display 11. The diffused beam illuminates the liquid crystal display 11 so that the liquid crystal display 11 allows at least a portion of the diffused beam to pass through, forming the image light beam 7.

[0038] The optical component 16 is a dedicated component formed in one piece and comprising, on one face, a reflective polarizer 17 and, on a second face opposite the first, an optical diffuser 18. Formed in one piece, it is understood that the optical component 16 consists of a single unit. A reflective polarizer is understood to be a polarizer operating by reflection, that is, reflecting a specific polarization component Pd and transmitting the orthogonal polarization component. An optical diffuser is understood to be an optical element that achieves angular spreading of incident light.

[0039] The first face is positioned on the side of the reflector 15, which corresponds to the side of the light source 14. This configuration improves the recycling of light within the backlighting device 10. Indeed, if a portion of the source beam does not have the polarization transmitted by the reflective polarizer, it is reflected by the reflective polarizer 17 and can be re-intercepted by the reflector 15, then reflected again towards the optical component 16.

[0040] One of the advantages of forming the optical component 16 in one piece is to limit reflections between the reflective polarizer 17 and the optical diffuser 18. Limiting these reflections improves the contrast perceived directly on the liquid crystal display 11.

[0041] For example, optical component 16 is obtained by the following process: - preparation of an intermediate part comprising a substrate provided with a reflective polarizer on one face; the reflective polarizer can be made of plastic, for example PVA-TAC-acrylic, and allows the light arriving on its surface to be transmitted in a given polarization and the light arriving in a polarization orthogonal to the given polarization. - engraving patterns on the second face of the substrate (opposite to the first face), for example by laser engraving, in order to form the optical diffuser 18 on this face; a diffusing structure can for example be printed on the back face (i.e. the face not directly receiving the incident light) of a reflective plastic polarizer, such as polycarbonate, by means of laser engraving, for example by laser machining (in English "Femtosecond laser patterning"); the diffusing structure corresponds to a graining distributed on the back face so as to diffuse the light according to a given diffusion distribution.

[0042] Figure 3 shows a substrate 25 with a reflective polarizer on one face 23. The substrate 25 has a transparent layer 24, here made of polycarbonate, defining a second face opposite the first face 23. It is proposed here to apply laser engraving to this second face to form an optical diffuser.

[0043] Figure 4 shows the substrate 25 of Figure 3 after laser etching of the second face defined by the transparent layer 24. The structured profile of the second face resulting from the laser etching can be observed. This structured profile provides an additional scattering function to the substrate equipped with the reflective polarizer.

[0044] In one variant, the reflective polarizer 17 is laminated to the optical diffuser 18 using a transparent optical adhesive. In this case, the optical diffuser 18 can be made of injection-molded plastic, such as polycarbonate. The thickness of the optical diffuser 18 in the optical component 16 can be between 0.2 mm and 1 mm, and preferably 0.5 mm. Alternatively, the optical diffuser 18 can be made of a plastic film, for example, polycarbonate. The film thickness can be between 0.1 mm and 0.25 mm, and preferably 0.125 mm. Preferably, the material of the optical diffuser 18 has a detection temperature greater than or equal to 120°C with a load of 1.8 MPa, and greater than or equal to 130°C with a load of 0.45 MPa.

[0045] To ensure the quality of the lamination of the reflective polarizer 17 onto the optical diffuser 18, the latter is preferably made of plastic and is heated to a temperature between 30°C and 60°C. This procedure reduces mechanical stresses inside the optical diffuser 18 and ensures better adhesion to the reflective polarizer.

[0046] For example, the thickness of the reflective polarizer 17 in the optical component 16 is less than or equal to 0.15 mm. Preferably, the thickness of the reflective polarizer 17 in the optical component 16 is equal to 0.075 mm.

[0047] Preferably, the reflective polarizer 17 can operate at temperatures greater than or equal to 105°C.

[0048] The optical diffuser 18 is defined by a diffusion indicator with maximum intensity in a principal direction, and, for example, angular widths in certain directions. For example, the type of diffusion achieved by the optical diffuser 18 is Gaussian elliptical. For example, the full width at half maximum (FWHM) of diffusion in the length direction of the liquid crystal display 11 is 30 degrees and the FWHM of diffusion in the width direction of the liquid crystal display 11 is 20 degrees.

[0049] The liquid crystal display 11 comprises a liquid crystal matrix interposed between an upstream polarizer 19 and a downstream polarizer 20, the upstream polarizer 19 being located on the side of the optical component 16. The upstream polarizer 19 is configured to selectively transmit a light component having upstream polarization Pa into the liquid crystal matrix. Appropriate activation of certain elements of the liquid crystal matrix allows the light received from the upstream polarizer 19 to pass through the liquid crystal matrix elements, or not, through the downstream polarizer 20.

[0050] The polarization determined Pd reflected by the reflective polarizer 17 is set orthogonally to the upstream polarization Pa. In other words, the polarization of the light Pt transmitted by the reflective polarizer 17 is aligned with the polarization direction transmitted by the upstream polarizer 19 of the liquid crystal screen 11. Figure 5 schematically illustrates this setting.

[0051] Thus, by choosing the optical diffuser 18 so that it minimally disturbs the polarization of the light it receives, the diffused beam has a polarization that will be transmitted by the upstream polarizer 19 of the liquid crystal display 11 and pass through it. In this way, the absorption of the diffused beam in the liquid crystal display 11 is reduced while its transmission is improved, which limits the heating of the liquid crystal display 11.

[0052] In this first embodiment, the reflector 15 has a constant height in the direction defined by the principal emission direction of the light source 14, thus that a main axis parallel to the main direction of emission D of the light source 14.

[0053] For example, the reflector 15 is made of plastic with a metallization layer applied to its inner walls. Preferably, the material of the reflector 15 has a detection temperature greater than or equal to 120°C with a load of 1.8 MPa and greater than or equal to 130°C with a load of 0.45 MPa. This preserves the mechanical and thermal properties of the reflector across the entire operating range of the image-generating device 6, for example, between -40°C and 105°C. Aluminum or silver can be used for the metallization.

[0054] For example, the reflectance coefficient of reflector 15 is greater than or equal to 60%, preferably greater than or equal to 80%. This parameter helps to reduce light loss through absorption and improves the uniformity of the virtual image 3.

[0055] The geometry of the reflector 15 can be optimized to improve the recycling efficiency of the reflective polarizer 17. Preferably, the shape of the reflector 15 is tapered, with the narrowest part positioned closer to the light source 14. For example, the reflector 15 may have walls whose inclination maximizes the reflective surface seen from the reflective polarizer 17. Also, the curvature of the walls of the reflector 15 can be optimized to improve the collimation of the source beam.

[0056] In this first embodiment, the optical component 16 is orthogonal to the main axis of the reflector.

[0057] Furthermore, the normal direction of the liquid crystal display 11 is inclined with respect to the direction of the main axis of the reflector 15.

[0058] Figure 6 illustrates a second embodiment of the backlighting device 6 according to the invention.

[0059] As in the first embodiment, the normal direction of the liquid crystal display 11 is inclined with respect to the direction of the main axis of the reflector 15.

[0060] In this second embodiment, the normal direction of the optical component 16 is also inclined with respect to the direction of the main axis of the reflector 15. For example, the inclination is between 12 degrees and 24 degrees. Preferably, the inclination is greater than 13 degrees.

[0061] For example, the optical component 16 is parallel to the liquid crystal display 11.

[0062] The geometry of reflector 15 is then adapted to this configuration so as not to degrade the optical characteristics of the perceived virtual image 3, such as contrast, luminance, and uniformity. As illustrated in Figure 6, the reflector always has a principal axis parallel to the principal direction of emission of the light source but is asymmetrical. For example, the edges of reflector 15 intercept a fictitious surface inclined at an angle of inclination with respect to a plane orthogonal to the principal axis of reflector 15. For example, the fictitious surface is parallel to the liquid crystal display 11.

Claims

Demands

1. Backlighting device (10) comprising: - a light source (14) configured to emit a source beam, - a reflector (15) configured to reflect at least a part of the source beam into a reflected beam, - a component (16) formed in one piece comprising, on a first face, a reflective polarizer (17) and, on a second face opposite to the first face, an optical diffuser (18), said component (16) being configured to receive and transmit at least part of the reflected beam, characterized in that the first face of the component (16) is placed on the side of the light source (14).

2. Backlighting device (10) according to claim 1, characterized in that the component (16) comprises a substrate with a first face carrying the reflective polarizer (17) and a second face opposite to the first face and in which the diffuser (18) is formed by etching.

3. Backlighting device according to claim 2, wherein the engraving is a laser engraving.

4. Backlighting device (10) according to claim 1, characterized in that the reflective polarizer (17) is laminated onto the optical diffuser (18).

5. Backlighting device (10) according to any one of claims 1 to 4, characterized in that the optical diffuser (18) produces a Gaussian elliptical type light diffusion.

6. Image generation device (6) comprising a backlighting device (10) according to any one of claims 1 to 5, characterized in that it further comprises a liquid crystal display (11) placed downstream of the reflector (15) in the path of propagation of the light, the liquid crystal display (11) comprising a liquid crystal matrix interposed between an upstream polarizer (19) and a downstream polarizer (20), said upstream polarizer (19) being capable of selectively transmitting a component of light having a given upstream polarization (Pa).

7. Image generation device (6) according to claim 6, characterized in that the reflective polarizer (17) is adapted to reflect a light component having a polarization orthogonal (Pr) to said upstream polarization (Pa).

8. Image generation device (6) according to claim 6 or 7, characterized in that the reflector (15) has a principal axis parallel to a direction principal (D) of the source beam and in that the component (16) is orthogonal to the principal axis of the reflector.

9. Image generation device (6) according to claim 6 or 7, characterized in that: - the liquid crystal display (11) is inclined with respect to the main direction (D) of the source beam, - the component (16) is positioned parallel to the liquid crystal display (11).

10. Head-up display (1) comprising an image generation device (6) according to any one of claims 6 to 9, further comprising an optical projection system (8) capable of reflecting a light beam generated by the image generation device towards a partially transparent blade (5).

11. Method of manufacturing a component (16) for a backlighting device (10) from a substrate having a reflective polarizer (17) on a first face and having a second face opposite to the first face, comprising a step of forming an optical diffuser (18) by etching in the second face of the substrate.

12. A manufacturing method according to claim 11, characterized in that the optical diffuser formation step is a laser engraving step.

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