Method and apparatus for manufacturing an optical element for generating a light distribution, method for manufacturing a master element and master element

Abstract

A method for producing an optical element is provided, which is configured to generate a light distribution with a predetermined caustic when irradiated with light. The method comprises arranging a photosensitive layer (34) adjacent to a master element (32), and illuminating the photosensitive layer (34) with incoherent light via the master element (32), wherein the optical element comprises the photosensitive layer (34). A corresponding apparatus, a method for producing a corresponding master element, and a corresponding master element are also provided.

Description

Technical field

[0001] The present application relates to methods and devices for manufacturing optical elements which, when irradiated with light, produce a light distribution with a predetermined caustic, i.e., predetermined caustic properties. Furthermore, the present application relates to a method for manufacturing a master element which can be used in the method for manufacturing the optical element, as well as a corresponding master element. background

[0002] In the context of this application, a caustic is understood to be a limitation of a light distribution produced by an optical system. In various applications, it is desirable to shape the light distribution of a light source so that it only covers a specific area, i.e., to exhibit a corresponding caustic.

[0003] An example of this is the automotive sector. Here, for instance, a specific area needs to be illuminated by a headlight. US patent 2023 / 029379 A1 discloses how to manufacture a plastic element by injection molding that has an optically effective surface capable of producing a desired light distribution.

[0004] In other applications, such as motorcycles as described in DE10 2021 132 110 B4 or projection applications as described in US 9 247 222 B2, a desired light distribution is achieved, in the latter case by microlenses. Deformed surfaces are also used to generate a light distribution in the security sector; see, for example, US 8 964 295 B2.

[0005] The production of the refractive surfaces required for the above applications can be comparatively expensive.

[0006] To shape and focus light, a thin, locally deformed surface can also be used. This can be created by appropriately processing a transparent plastic. The principle of such light shaping is described in Fig. 5 shown.

[0007] The Fig. Figure 5 shows a transparent optical element 51, typically made of a transparent plastic, with a flat side 52 and a locally machined side 53, the latter being machined to have a desired surface shape. Light from a light source 50 is refracted through the machined surface 53 to produce a desired light distribution in a projection plane 55, which may consist, for example, of Gaussian caustics, one of which is a Gaussian caustic 54 shown, produced by light refraction at a section 56 of the side 53. Further details of such an approach can be found in US 9,188,783 B2 or US 10,732,405 B2, the latter document specifically addressing the calculation of such surfaces.

[0008] Processing such surfaces to achieve the desired optical effect is comparatively complex and hardly suitable for mass production.

[0009] Therefore, there is a need for improved methods and devices for the manufacture of such optical elements and related techniques.

[0010] A method for manufacturing an optical element according to claim 1, a method for manufacturing a master element for such a method according to claim 6, a master element according to claim 11, and a device according to claim 13 are provided. The dependent claims define further embodiments.

[0011] According to one embodiment, a method for manufacturing an optical element is provided which is configured to generate a light distribution with a predetermined caustic when irradiated with light. The method comprises: Arranging a photosensitive layer adjacent to a master element, and exposing the photosensitive layer with incoherent light via the master element, wherein the optical element to be produced comprises the photosensitive layer.

[0012] In this method, the optical element's property of generating light distribution is not created by a modified surface, but rather by a refractive index profile resulting from a predetermined, uneven exposure of a photosensitive layer. Using a master element enables high-throughput production. This process is similar to the production of holograms by replicating a master hologram, except that, unlike hologram replication, incoherent light is used in this case.

[0013] The use of incoherent light suppresses interference effects, which are essential for hologram replication. In contrast, the method described above generates a desired intensity distribution without interference effects in the photosensitive layer, thus creating the refractive index profile. Incoherent light is specifically defined as light with a coherence length less than or equal to the thickness of the photosensitive layer, in order to suppress interference effects. For example, light-emitting diodes (LEDs) can be used as light sources. LED coherence lengths can range from approximately 4 µm to 8 µm for red LEDs and from approximately 20 µm to 28 µm for green LEDs, and the thickness of the photosensitive layer can be greater than these coherence lengths (e.g., greater than 30 µm, greater than 50 µm, or greater than 100 µm).

[0014] A photosensitive layer is a layer that changes its refractive index when irradiated with light in a specific wavelength range. Such photosensitive layers can comprise one or more photopolymers.

[0015] The photosensitive layer can consist of a photosensitive material, which may have a first component and a second component. The first component may exhibit a higher refractive index change upon exposure and / or a higher rate of refractive index change upon exposure. By composing the photosensitive material from multiple components with different refractive indices, rates of change, and / or other properties, the material's characteristics can be varied. Furthermore, this allows for finer adjustment of the final refractive index in the gradient-index microlenses.

[0016] The first and second components can be monomers. A material system can consist of an acrylate mixture or a hybrid system with epoxy, epoxy hardener, silicon-containing and sulfur-containing monomers (also oligomers, polymers), and ethylene double bonds. The material system can include, for example, the following materials: - UV epoxy - Acrylate - SH-EN (material consisting of thiols and alkenes) - UV epoxy mixtures - Epoxy - Silane - Silicones

[0017] SH-EN materials are light-curing systems consisting of thiols and alkenes. Thiols can be monomers with a suitable refractive index and are therefore suitable for the process.

[0018] After exposure, the photosensitive layer can be fixed. For example, this involves irradiating the photosensitive layer with light in a different wavelength range than that used for exposure, a process known as bleaching. In other embodiments, fixing can be achieved alternatively or additionally through heat treatment. The fixing method used depends on the specific photosensitive material. Fixing prevents the refractive index distribution created by exposure from changing when light falls on the photosensitive layer during subsequent use.

[0019] The exposed and, if necessary, fixed photosensitive layer, for example arranged on a transparent substrate, then serves as the optical element. Exposure thus creates a refractive index distribution in the photosensitive layer, which causes the photosensitive layer to produce the light distribution when irradiated with light.

[0020] "Via the master element" means that the master element shapes the light from a light source for exposure. For example, the light can pass through the master element. However, it is also possible to use a master element that works by reflection.

[0021] A suitable device for manufacturing an optical element is also provided, comprising a light source, a holder for the master element described above, and a holder for the photosensitive layer. A corresponding master element is then provided, and various photosensitive layers can be exposed as described above to carry out serial production of optical elements.

[0022] The master element can be a master element with an additional exposed photosensitive layer, a printed master element with material areas exhibiting different refractive indices, or a master element with a surface shape that generates the required light distribution for exposing the photosensitive layer. Thus, various types of master elements are possible.

[0023] According to a further embodiment, a method for manufacturing a master element is disclosed, which can be used for the manufacturing of the optical element described above. The method for manufacturing the master element comprises: - Calculating a configuration of the master element which, when a photosensitive layer is exposed to incoherent light through the master element, generates a refractive index distribution in the photosensitive layer which, when irradiated with light, produces the light distribution with the specified caustic, and - Creating the master element with the calculated configuration.

[0024] First, a configuration for the master element is determined. The type of configuration depends on the type of master element. In some embodiments, the master element itself can be defined by a specific refractive index distribution. In this case, calculating the configuration is equivalent to calculating a refractive index distribution. For fabrication, the master element can then be printed with the corresponding refractive index distribution, for example, using inkjet technology, where different materials (inks) have different refractive indices. Alternatively, such a refractive index distribution can also be created in the master element by exposing an additional photosensitive layer.In other embodiments, the master element has a surface shape; that is, the light used to expose the photosensitive layer is generated by an interface between the master element and air (which also corresponds to a refractive index change). In such a case, calculating the configuration is equivalent to calculating the surface shape. A master element with a corresponding surface shape can then be produced by machining a transparent material (milling, laser processing, etc.) or, for example, by 3D printing.

[0025] The configuration calculation is generally based on the following considerations: From a light distribution with a desired caustic pattern that the optical element is intended to generate, a corresponding refractive index distribution for the optical element can be calculated. Examples of principles for such calculations are also disclosed in US91887883 and US10732405. Other approaches, such as those known from the calculation of microlenses, can also be used. From the properties of the photosensitive layer—that is, which refractive index change can be induced by which local exposure of the photosensitive layer—a light distribution is then obtained that the master element must generate for exposure. From this light distribution, a refractive index distribution or a surface shape for the master element can then be determined, for example, using similar principles to those described above for the photosensitive layer.The above steps can also be performed in a single calculation; therefore, it is not necessary to explicitly perform multiple calculation steps.

[0026] In addition, a corresponding master element is also provided. Brief description of the drawing figures

[0027] Several exemplary embodiments will now be explained in more detail with reference to the accompanying drawings. These show: Fig. 1 a flowchart of a process according to an exemplary embodiment, Fig. 2 a flowchart of a process according to a further embodiment, Fig. 3 an embodiment of a device for carrying out the method of Fig. 1, Fig. 4 an embodiment of a device for carrying out step 21 of the Fig. 2, and Fig. 5. A diagram to illustrate a machined surface to create a caustic.

[0028] The Fig. Figure 1 shows a method for manufacturing an optical element which, when irradiated with light, produces a light distribution with a predetermined caustic, according to an exemplary embodiment. Fig. Figure 3 shows a corresponding device. Although the method can also be used with devices other than the one shown in Figure 3. Fig. The procedure, as shown in 3, can be carried out; for better understanding, the procedure will be explained together with the Fig. 3 explained.

[0029] In step 10, a photosensitive layer is positioned adjacent to a master element. "Adjacent" in this context does not mean immediately adjacent; in particular, the layer can be positioned at a predetermined distance. In the exemplary embodiment of the Fig. In this process, a photosensitive layer 34, for example made of one or more photopolymers, is used, which is located on a transparent support 35. The transparent support 35 can be made of, for example, a plastic or glass. The combination of photosensitive layer 34 and transparent support 35 is arranged at a predetermined distance 33 from a master element 32.

[0030] In step 11 of the Fig. 1. The photosensitive layer is then illuminated via a master element using incoherent light. In the example of the Fig. In step 3, incoherent light of a corresponding wavelength is generated by a light source 30, for example, a light-emitting diode, and collimated by an optical system 31. This collimated light beam then passes through the master element 32 and onto the photosensitive layer 34. The master element 32 generates a light distribution that modifies the refractive index of the photosensitive layer 34, ultimately creating the desired optical element. After exposure, the photosensitive layer 34 can be fixed so that the generated refractive index profile remains unchanged even after subsequent exposure to light.

[0031] To produce the master element 32, the following can be used: Fig. The two described methods are used. In step 20, a configuration for the master element is calculated, as already explained above in the general section. In step 21, the master element is then manufactured with the configuration calculated in step 20.

[0032] As explained above, one possibility is that the configuration is a refractive index distribution for the master element. In this case, the master element can be created by exposing another photosensitive layer. This is in the Fig. 4 shown. In the Fig. 4 is another photosensitive layer 44, in which the refractive index distribution for the master element is to be generated, arranged on a transparent substrate 45. For exposure, light is generated by a light source 40. The light source 40 has a wavelength matched to the photosensitive layer 44. The light source 40 can, for example, be one or more light-emitting diodes. Light from the light source 40 is collimated by optics 41 and spatially modulated by a spatial light modulator (SLM) 42, according to a refractive index distribution to be generated in the master element. The wavelength of the light source 40 corresponds to the wavelength used for the corresponding exposure calculation.A liquid crystal display, for example, can be used as a transmittive spatial light modulator. In other embodiments, a reflective configuration, such as a micromirror arrangement, can also be used. The modulated light is focused by a focusing optic 43 onto an area 46 to induce a corresponding change in the refractive index there. By moving the elements 40 to 43 relative to the photosensitive layer 44, a larger area can then be described. Here, too, fixation can take place after exposure.

[0033] As already mentioned, a desired refractive index distribution for the master element can alternatively be provided by an inkjet printing process, or instead of a refractive index distribution, a surface shape can be calculated as a configuration, which can then be created by machining a smooth surface or by 3D printing.

[0034] Since the relatively complex production of the master element only needs to be done once, and then the optical elements can be produced by simple replication as described in the Fig. 1 and Fig. As explained in section 3, this makes high-throughput production of optical elements 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] US 2023 / 029379 A1

[0003] DE 10 2021 132 110 B4

[0004] US 9 247 222 B2

[0004] US 8 964 295 B2

[0004] US 9 188 783 B2

[0007] US 10 732 405 B2

[0007] US 10732405

[0025]

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