Methods and arrangements for reducing external stray light and their use

Abstract

The invention relates to a method for reducing external stray light incident on an optical system (1), comprising the following steps: providing an optical system (1) in which imaging of a light source is ensured; positioning a transparent, plate-shaped light guide (3) in the optical system (1), wherein the light guide (3) has structural elements (6) on at least one of its large surfaces (3a, 3b) and / or within its volume, and each structural element (6) has at least one functional surface for the defined deflection of light, at which stray light is coupled into the light guide (3) and / or deflected from the optical axis, whereby stray light coupled into the light guide (3), if present, is coupled out again and / or absorbed at one or more surfaces of the light guide (3).such that at least 10% of the interfering light incident on the optical system (1) is coupled into the optical fiber (3) and thus removed from the optical path of the optical system (1), and such that the imaging of the light source is disturbed due to the limited scattering of the optical fiber (3) to such an extent that the Michelson contrast of the imaging of the optical system (1) is reduced by no more than a factor of 2. The invention further comprises an arrangement implementing the method and the use of the method or the arrangement in a head-up display.

Description

Technical field of the invention

[0001] The problem is that sunlight enters optical systems such as head-up displays, leading to unacceptable artifacts. Description of the invention

[0002] The object of the invention is therefore to describe a method and arrangement that reduce stray light incident on optical systems, while simultaneously minimizing disturbance to the imaging process taking place by means of the optical system. In other words, it aims to describe a type of light-emitting diode.

[0003] This problem of the invention is solved according to the invention by a method according to the preamble of claim 1. Further embodiments are given in dependent claims 2 to 8.

[0004] The object of the invention is further solved according to the invention by an arrangement according to the preamble of claim 9.

[0005] Furthermore, the preamble of claim 10 describes a possible use of the aforementioned method or arrangement.

[0006] Furthermore, the invention also includes a method for manufacturing an optical fiber for use in a aforementioned method or arrangement, comprising the following steps - In a first alternative: manufacturing a light guide in an injection molding process (e.g. variothermal or isothermal injection molding or injection compression molding) using a mold insert which has the inverse structure of the structural elements present in / on the light guide and molds this structure into the light guide, - in a second alternative: manufacturing an optical fiber using a nano-imprint process (e.g., plate-to-plate, roll-to-plate, or roll-to-roll process; the latter with subsequent application to a substrate) using a structural insert (e.g., a roller or a plate) which has the inverse structure of the structural elements present in / on the optical fiber and imprints this structure onto the optical fiber, as well as - optional: Removal of edge areas, e.g. by cutting, sawing or punching out.

[0007] In general, structural elements of the optical fiber can have a three-dimensional shape with a maximum extent in their largest dimension that is less than 100 micrometers, preferably less than 50 micrometers.

[0008] Furthermore, such structural elements can be designed as depressions or raised areas on one (or both) of the large surfaces of an optical fiber, whereby depressions and raised areas can also be present on one and the same optical fiber or at least one of its large surfaces. Preferably, however, the structural elements are designed as depressions on one of the large surfaces of an optical fiber. It is also possible for structural elements to be located on both large surfaces and / or additionally, optionally, within the volume.

[0009] Furthermore, it is advantageous for the application if an optical fiber exhibits a stronger scattering behavior in a selectable direction than in a direction perpendicular to it.

[0010] A light guide preferably consists of a transparent, thermoplastic or thermoelastic polymer, e.g., plastic, or glass. For example, a light guide or its substrate can comprise at least 40% by weight of polymethyl methacrylate, preferably at least 60% by weight of polymethyl methacrylate. Alternatively, it can be, for example, polycarbonate (PC).

[0011] Furthermore, it is possible to attenuate any optical artifacts that may occur, for example those resulting from the manufacture of the optical fiber or its structural elements, by means of an anisotropic diffuser located in the optical path of the stray light in front of or behind the optical fiber.

[0012] The structural elements can be distributed in or on an optical fiber in various ways, either before or during its manufacture, according to adaptable and predefined conditions for coupling the interfering light into the fiber. These structural elements are locally confined structural modifications within the volume and / or on the surfaces of the optical fiber. Specifically excluded from the term "structural element" are additional optical layers applied to the surfaces of the optical fiber, such as diffusion layers, reflection layers, (dual) brightness-enhancing collimating layers (brightness enhancement film - BEF), or polarization-recycling layers, such as polarization-selective Bragg mirrors (dual brightness enhancement film - (D)BEF) or wire-grid polarizers.These additional layers, which do not fall under the definition of a "structural element," are connected to an optical fiber only at their edges, if at all. In the large areas, they usually just lie loosely on top and do not form a physical unit with the optical fiber. In contrast, coatings applied to the large areas, which bond with the optical fiber through chemical reactions or other forces (e.g., van der Waals forces), form a physical unit and are inseparable; such coatings are therefore not considered additional layers in the sense described above.

[0013] The number and extent of the structural elements are selected such that the light guide exhibits an average haze value of less than 20%, preferably less than 15%, and particularly preferably less than 10%, over at least 50%, preferably 80%, and most preferably over its entire surface, as measured according to ASTM D1003 – where the measurement is based on the more common procedure A using a hazemeter as a reference. This results in only minimal scattering of light passing through the light guide across its large surface areas. "Minimal" scattering means, for example, that (due to the low haze value) within an angular range of, for example, ±40° horizontally from the surface normal, a maximum of 1% to 5% of the luminance is added by scattering of light from the light guide itself, which is incident at a perpendicular angle across a large surface area.

[0014] Alternatively, the number and extent of the structural elements can be such that the optical fiber scatters at most 25 percent, preferably at most ten percent, of the light passing through its large areas by more than ten degrees (preferably only 7°, particularly preferably only 5°) over at least 80% of its area.

[0015] The structural elements themselves can also be designed, for example, as cavities formed within the volume of an optical fiber. These cavities can be evacuated, but are preferably filled with a gaseous, liquid, or solid material. The material has a refractive index that differs from that of the material used for the optical fiber; preferably, it is lower. The filling material and the choice of material allow for influencing the light transmission or coupling. Alternatively or additionally, the haze value of the material also preferably differs from that of the material used for the optical fiber and is preferably higher. Advantages of these configurations include higher efficiency in light coupling.

[0016] Alternatively, and in a technically simpler way, the cavities can also be formed by constructing an optical fiber from two bonded substrate layers, preferably of the same type. The bond can be chemical, physical, or adhesive. The cavities are then formed as material recesses at at least one of the interfaces between the substrate layers.

[0017] If the structural elements are applied to at least one of the large surfaces of an optical fiber, they are advantageously formed from a tool-structured plastic or glass, the structure of which was imprinted by means of a tool. This is possible, for example, in mass production by applying a UV-curing material—e.g., a lacquer, a monomer, etc.—to an optical fiber substrate, which is then structured by means of a tool and cured, e.g., polymerized, by UV radiation. Other radiation-curing materials can also be used. The formation of the recesses for realizing the structural elements can be achieved, for example, mechanically, lithographically, or using printing techniques, or by material deposition, conversion, ablation, or dissolution.In particular, variants of injection molding (variothermal / isothermal, injection compression molding / injection molding) can be used with the aid of appropriate structural inserts (see also DE102020134055 B4 of the applicant).

[0018] This allows for the cost-effective and mass-producible implementation of three-dimensional structural elements – either convex with the plastic component facing outwards on the surface, and / or concave as an indentation or recess within the surface layer of the structured plastic. Both concave and convex structures can be used.

[0019] The structure of the structural elements is specified according to the criteria mentioned above, whereby the effect of each structural element is known at least approximately and the properties of the optical fiber or the light entering the optical fiber can be specifically determined by a predefinable structure and distribution of the structural elements, whereby the ratio of the sum of the areas of the functional surfaces to the area of ​​the total surface of the large area into which light is coupled, as well as the shapes of the functional surfaces, are particularly important.

[0020] The required properties for the structural elements with regard to their number per unit area, their shape including the functional area, their orientation and extent in three dimensions, as well as their distribution on at least one of the large areas and / or within the volume of the light guide, can be determined, for example, with an optical simulation software such as "LightTools" from Synopsis or other providers and then physically implemented accordingly.

[0021] Furthermore, the structural elements can also consist of a different material, e.g., nanoparticles such as titanium dioxide or barium dioxide. In this case, the functional area is a part or the entirety of its surface.

[0022] The method or arrangement according to the invention can, for example, be used in a head-up display in a vehicle to minimize or completely suppress stray light from the sun. Other applications are possible.

[0023] In principle, the performance of the invention is maintained if the parameters described above are varied within certain limits.

[0024] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations given, but also in other combinations or on their own, without leaving the scope of the present invention. Brief description of the drawings

[0025] The invention is explained in more detail below with reference to exemplary embodiments and the accompanying drawings, which also disclose essential features of the invention. These exemplary embodiments serve only for illustration and are not to be interpreted as limiting. For example, a description of an exemplary embodiment with a plurality of elements or components is not to be interpreted as meaning that all of these elements or components are necessary for implementation. Rather, other exemplary embodiments may also contain alternative elements and components, fewer elements or components, or additional elements or components. Elements or components from different exemplary embodiments may be combined with one another unless otherwise specified. Modifications and variations described for one of the exemplary embodiments may also be applicable to other exemplary embodiments.To avoid repetition, identical or corresponding elements in different figures are designated with the same reference symbols and are not explained multiple times. Furthermore, none of the drawings are to scale. They show: Fig. 1. A schematic diagram of a top view of the external structure of exemplary structural elements, Fig. 2. A schematic diagram in sectional view for an exemplary implementation of the method or arrangement, as well as Fig. 3 a qualitative simulation for the penetration of a fiber optic cable with light entering it through one of the two large surfaces. Detailed description of the drawings

[0026] The Fig. Figure 1 shows a schematic diagram of a top view of the external structure of exemplary structural elements 6 of an optical fiber 3. These structural elements can, for example, have the three-dimensional external shape of prisms which, when viewing the optical fiber 3 perpendicular to one of its large surfaces 3a, 3b, form the Fig. The base area shown in section 1 is shown. Other embodiments of the structural elements 6 are also within the scope of the invention.

[0027] An example of a method for reducing external stray light incident on an optical system, where the stray light is incident at an angle to an optical axis of the optical system (within a tolerance of + / -85°), is described below using the following: Fig. 2 explains. This shows a schematic diagram in sectional view for an exemplary implementation of the procedure, which comprises the following steps. - Providing an optical system 1 in which an image of a light source is ensured by means of at least one (not shown in the drawing) lens, a hologram, a diffractive grating, a prism grid, a lens grid and / or a mirror, - Positioning of a transparent, plate-shaped light guide 3 in the optical system 1, - wherein the optical fiber 3 has two large surfaces 3a, 3b and narrow sides connecting the large surfaces 3a, 3b at their edges, wherein - the optical fiber 3 (in this example) has structural elements 6 (e.g. in the form of microprisms) on its large surface 3a, and - each structural element 6 has at least one functional surface for the defined deflection of light, at which stray light is coupled into the light guide 3 and / or deflected from the optical axis, - whereby any interference light coupled into the optical fiber 3, if present, is coupled out again and / or absorbed at one or more surfaces of the optical fiber 3, (In Fig. 2 This is indicated by the narrow horizontal arrow in the optical fiber 3; the corresponding light is guided in the optical fiber 3 by total internal reflection to its (in this case right) narrow side and, in this example, intentionally coupled out there; this dissipated stray light can then usually no longer generate artifacts. It can, for example, be directed onto an absorber. - furthermore, wherein the optical fiber has an average haze value of less than 30% over at least 80% of its surface (preferably less than 20%, particularly preferably less than 10%), as measured according to ASTM D1003, - so that i. at least 10% (preferably 25%, particularly preferably more than 50%) of the stray light incident on the optical system 1 is coupled into the optical fiber 3 and thus removed from the optical path of the optical system 1, (this is in Fig. 2 is marked by the thick arrow labeled "External Stray Light", whereby after passing through the light guide 3 only a narrow arrow is shown, synonymous with significantly reduced stray light in the optical system 1. Only a small reflection component, originating from reflections at the upper large surface 3b, is indicated by a narrow arrow pointing in the opposite direction. ii. the said imaging of the said light source by means of a lens, a hologram, a diffractive grating, a prism grid, a lens grid and / or a mirror is disturbed due to the limited scattering of the optical guide 3 to such an extent that the Michelson contrast of the imaging of the optical system 1 is reduced by no more than a factor of 2. (In Fig. 2. The "light from the light source" is shown with a thick arrow; this light can pass through the optical fiber 3 essentially undisturbed, which is why, viewed from below, a thick arrow is still shown after the optical fiber 3. Only a small reflection component, which originates from reflections at the lower large surface 3a, is indicated with a thin arrow in the opposite direction.

[0028] In special embodiments, it is also possible that at least 10% (preferably 25%, particularly preferably more than 50%) of the interfering light incident on the optical system 1 is not coupled into the light guide 3, but is nevertheless deflected by the structural elements 6 and thus removed from the optical path of the optical system 1.

[0029] Advantageously, the optical fiber 3 has an anti-reflective coating on at least one of its large surfaces 3a and / or 3b.

[0030] The light source could be, for example, an image display device.

[0031] In the Fig. Figure 3 is a qualitative simulation of the penetration of an optical fiber 3 by light entering it through one of the two large surfaces 3a, 3b. The ordinate corresponds to a normalized transmission quantity, where the value at the bottom is zero (no transmission) and the value at the top is 1 (complete transmission). The abscissa shows the angle of the functional surfaces of exemplary structural elements 6, here the prism angle to the base in the case of microprisms as structural elements 6.

[0032] Assuming, for example, that the optical fiber 3 (in this example) has structural elements 6 on its large surface 3a that couple external interference light into it, the solid curve in Fig. The graph qualitatively describes the transmission when light is incident perpendicularly into the optical fiber 3 on the (upper) large surface 3b and partially penetrates it. Furthermore, the dashed curve qualitatively describes the transmission when light (especially from the light source) is incident perpendicularly into the optical fiber 3 on the (lower) large surface 3a and at least partially penetrates it. It can be seen that the transmission behavior of the optical fiber 3 is partially asymmetrical with respect to the incidence via the two large surfaces 3a and 3b: When light is incident perpendicularly into the optical fiber 3 on the (upper) large surface 3b, the transmission is significantly reduced at angles of approximately 45° to the functional surface of exemplary structural elements 6, whereas light incident perpendicularly into the optical fiber 3 on the (lower) large surface 3a is transmitted with a high degree of transmission even at these angles.These relationships reverse at approximately 75° as the angle of the functional surface of exemplary structural elements 6, so that, depending on the application, in particular depending on the angle of incidence of the interfering light, an optical fiber 3 can be placed in the optical system 1. The transmission examples in . Fig. The three examples are purely illustrative; for other types of structural elements, the effects can also be achieved at other angles or angle ranges.

[0033] Furthermore, it is possible to incorporate several optical fibers 3 into the optical system 1 in order to remove even more stray light from the optical system 1 without significantly disturbing the imaging of the optical system 1.

[0034] The drawings Fig. Paragraphs 1-3 can also be used to explain a corresponding arrangement. For reasons of redundancy, the text applicable to the procedure is not repeated here.

[0035] The method and arrangement described above solve the problem: Both are able to reduce stray light entering optical systems, while disturbing the imaging taking place simultaneously by means of the optical system as little as possible.

[0036] The method or arrangement according to the invention can, for example, be used in a head-up display in a vehicle to minimize or completely suppress stray light from the sun. Other applications are possible. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 102020134055 B4

[0017]

Claims

[1] Method for reducing external stray light incident on an optical system (1), wherein the stray light is incident to a tolerance of + / -85° opposite to an optical axis of the optical system (1), comprising the following steps - Providing an optical system (1) in which an image of a light source is ensured by means of at least one lens, a hologram, a diffractive grating, a prism grid, a lens grid and / or a mirror, - Positioning of a transparent, plate-shaped light guide (3) in the optical system (1) or - when viewed from the direction of the interfering light source - in front of the optical system (1), - wherein the optical fiber (3) has two large surfaces (3a, 3b) and narrow sides connecting the large surfaces (3a, 3b) at their edges, wherein - the optical fiber (3) has structural elements (6) on at least one of its large surfaces (3a, 3b) and / or within its volume, and - each structural element (6) has at least one functional surface for the defined deflection of light, at which stray light is coupled into the light guide (3) and / or deflected from the optical axis, - whereby any interference light coupled into the optical fiber (3) is coupled out again and / or absorbed at one or more surfaces of the optical fiber (3), - wherein furthermore the optical fiber (3) has an average haze value of less than 30% over at least 80% of its surface, as measured according to ASTM D1003, - so that i. at least 10% of the interfering light incident on the optical system (1) is coupled into the optical fiber (3) and thus removed from the optical path of the optical system (1), ii. the said imaging of the said light source by means of a lens, a hologram, a diffractive grating, a prism grid, a lens grid and / or a mirror is disturbed due to the limited scattering of the optical guide (3) at most to such an extent that the Michelson contrast of the imaging of the optical system (1) is reduced by no more than a factor of 2. [2] Method according to claim 1, characterized by , that at least one narrow side of the optical fiber (3) is covered with an absorber which at least partially absorbs the interference light coupled into the optical fiber (3) after transmission in the optical fiber (3) due to total reflection and subsequent coupling out at one narrow side. [3] Method according to any of the aforementioned claims, characterized by , that the optical fiber (3) has an anti-reflective coating on at least one of its large surfaces (3a, 3b). [4] Method according to any of the aforementioned claims, characterized by that the light source is an image display device. [5] Method according to any of the aforementioned claims, characterized by , that the optical fiber (3) exhibits a stronger scattering behavior in a selectable direction than in a direction perpendicular to it. [6] Method according to any of the aforementioned claims, characterized by , that the structural elements (6) of the optical fiber (3) have the form of microprisms, preferably deformed microprisms. [7] Method according to any one of claims 1 to 5, characterized by , that the structural elements (6) of the optical fiber (3) are diffraction gratings. [8] Method according to any one of claims 1 to 5, characterized by , that the structural elements (6) of the optical fiber (3) are particles of a different material than the material of the optical fiber (3). [9] arrangement, encompassing - an optical system (1) in which an image of a light source is provided by means of at least one lens, a hologram, a diffractive grating, a prism grid, a lens grid and / or a mirror, wherein external stray light - up to a tolerance of + / -85° opposite to an optical axis of the optical system (1)- is incident into this optical system, - furthermore a transparent, plate-shaped light guide (3) in the optical system (1) or - when viewed from the direction of the interfering light source - in front of the optical system (1), - wherein the optical fiber (3) has two large surfaces (3a, 3b) and narrow sides connecting the large surfaces (3a, 3b) at their edges, wherein - the optical fiber (3) has structural elements (6) on at least one of its large surfaces (3a, 3b) and / or within its volume, and - each structural element (6) has at least one functional surface for the defined deflection of light, at which stray light is coupled into the light guide (3) and / or deflected from the optical axis, - whereby any interference light coupled into the optical fiber (3) is coupled out again and / or absorbed at one or more surfaces of the optical fiber (3), - wherein furthermore the optical fiber (3) has an average haze value of less than 30% over at least 80% of its surface, as measured according to ASTM D1003, - so that i. at least 10% of the interfering light incident on the optical system (1) is coupled into the optical fiber (3) and thus removed from the optical path of the optical system (1), ii. the said imaging of the said light source by means of a lens, a hologram, a diffractive grating, a prism grid, a lens grid and / or a mirror is disturbed due to the limited scattering of the optical fiber to such an extent that the Michelson contrast of the imaging of the optical system (1) is reduced by no more than a factor of 2. [10] Use of the method according to any one of claims 1 to 8 or the arrangement according to claim 9 in a head-up display.

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