"sequential exposure of hologram stacks"

Abstract

The invention relates to a method for replicating a polychromatic hologram combination, comprising the following steps: providing a first master hologram which is designed for a first wavelength range, and providing a second master hologram which is designed for a second wavelength range; providing a replication combination comprising a first light-sensitive layer on a replication substrate; exposing the first master hologram to obtain a first replicated hologram in the first light-sensitive layer by means of light of the first wavelength range; fixing the first replicated hologram in the first light-sensitive layer; applying a second light-sensitive layer onto the first light-sensitive layer; exposing the second master hologram to obtain a second replicated hologram in the second light-sensitive layer by means of light of a second wavelength range; fixing the second replicated hologram in the second light-sensitive layer. The invention also relates to a replication combination comprising at least a first and a second replicated hologram, which replication combination can be produced by means of the method according to the invention.

Description

[0001] “SEQUENTIAL EXPOSURE OF HOLOGRAM STACKS”

[0002] DESCRIPTION

[0003] The invention relates to a method for the replication of a polychromatic hologram composite comprising the following steps: providing a first master hologram designed for a first wavelength range and a second master hologram designed for a second wavelength range, providing a replication composite with a first light-sensitive layer on a replication substrate, exposing the first master hologram to obtain a first replicated hologram in the first light-sensitive layer by means of radiation of the first wavelength range, fixing the first replicated hologram in the first light-sensitive layer, applying a second light-sensitive layer to the first light-sensitive layer, exposing the second master hologram to obtain a second replicated hologram in the second light-sensitive layer by means of radiation of the second wavelength range,Fixing the second replicated hologram in the second light-sensitive layer. The invention further relates to a replication composite comprising at least a first and a second replicated hologram, wherein the replication composite can be produced by the method according to the invention.

[0004] Background and state of the art

[0005] The invention relates to the field of hologram replication.

[0006] Holograms are created by the interference of a reference beam with light reflected or diffracted from the surface of an object (object rays). Traditionally, three-dimensional objects have been used to create unique, customized holograms. Commercially available holograms, however, are often mass-produced using duplication processes. Such duplication processes typically use a master hologram, which has a diffraction pattern to be copied. The diffraction pattern can be configured to diffract radiation of a single wavelength or a narrow range of wavelengths (monochromatic) or multiple wavelengths (polychromatic). In the case of a polychromatic diffraction pattern, a master hologram can be created step by step using lasers of different wavelengths.For this purpose, the diffraction pattern can be divided into color channels, which are recorded in a single layer or each represent a separate layer of a multilayer stack. It is also possible for the color channels to form separate master holograms, which are not arranged as a stack, but rather next to each other or in different workstations of a duplication process. The master holograms can be in film form. The master holograms used are often stored in or on a substrate body which bears the master hologram. The substrate body is preferably rigid, transparent and can have various shapes, for example a cuboid, a plate or a cylinder. The combination of the master hologram (or master holograms) with the substrate body forms a master composite.

[0007] The master composite is exposed to a coherent light source to replicate the diffraction pattern from the master hologram in a photosensitive material, wherein the photosensitive material is provided, for example, in layer form, in particular as a composite with one or more carrier films. The photosensitive material can be sensitive to radiation within a specific wavelength range, for example, the wavelength range of a specific color (e.g., red, green, or blue). Photosensitive materials are also known that are sensitive to the entire visible spectrum. For mass production, the photosensitive composite can be provided in the form of a flowing web comprising a photosensitive material and one or more carrier or protective layers.For this purpose, the light-sensitive web is transported through various workstations to produce the HOEs (Holographic Optical Elements).

[0008] During exposure, the composite web is brought into optical contact with a surface of the master composite. "Optical contact" should ideally allow a ray of light to pass between process components without experiencing significant reflections or even total internal reflection. Direct, integral contact between the process components is possible, but not necessary. Preferably, neither reflection (especially total internal reflection) nor scattering occurs at the interface between the surfaces of adjacent process components.

[0009] To create a reflection hologram, the coherent light can traverse the composite path before reaching the master hologram, which reflects it back into the composite path. The object and reference beams interfere with each other in the light-sensitive material, forming the replicated hologram. The replication process is sensitive to changes in exposure angle, intensity, wavelength, etc., which must be adjusted according to the optical function of the master hologram. Typically, the exposure for each master hologram is performed according to a set of preprogrammed parameters.

[0010] HOEs (holographic optical elements) typically refer to optical components in which holographic properties are used to achieve a specific light beam path, such as transmission, reflection, diffraction, scattering, and / or deflection, etc. This allows desired optical functionalities to be implemented compactly in any substrate. The holographic properties preferably exploit the wave nature of light, particularly coherence and interference effects. Both the intensity and phase of the light are taken into account.

[0011] For example, HOEs can be configured to perform the optical function of a classic optical component such as a lens or a mirror. However, due to their thin construction, they can be much more compact than conventional optical components. They can also be designed to avoid the well-known optical errors of conventional optical components, such as spherical aberration and chromatic aberration. For example, HOEs can convert a plane wavefront into a spherical one and vice versa. They require very little space and can be easily integrated into a surface such as a window, eyeglasses, a card, or other product surfaces. To perform the optical function without the optical errors of conventional components, the HOEs must be highly efficient and all channels must be precisely aligned.However, the known techniques for creating HOEs usually lead to quality and / or alignment errors.

[0012] For some applications, it may be desirable for the HOEs to be exposed in multiple layers or with multiple superimposed patterns or wavelengths (e.g., color channels). In some cases, a hologram can contain a polychromatic diffraction pattern in the form of Bragg gratings at different frequencies in a single layer of material. Such a hologram can be recorded simultaneously at multiple wavelengths, for example, as an RGB or CMY hologram. The polychromatic hologram can be copied from a polychromatic RGB or CMY master hologram, which can be a single layer or a stack of holograms with different wavelengths. This would require the use of a light-sensitive material sensitive to all color channels used.However, such materials are often not equally sensitive to all wavelengths and may not offer the highest image resolution across the entire wavelength range. At the same time, the quality of the produced polychromatic hologram is limited by the quality of the master composite from which it was copied. If the various holograms, layers, and / or channels of the master composite are not precisely aligned, the alignment error is copied into the light-sensitive material. Depending on the manufacturing process used, the errors can even be further amplified. This can severely limit the positional accuracy of the replicated polychromatic hologram.

[0013] As explained below, it is known in the art to form the multiple channels of the master composite by separately created master holograms, which are then stacked and laminated on top of each other. The lamination process often deforms the layers and changes their positions relative to each other, so that the channels are no longer perfectly aligned. If the channels are "multiplexed" (or superimposed) within a single light-sensitive layer, the exposure of the different channels must also be perfectly coordinated. This is difficult to achieve in practice. If several master holograms are produced as a multiplexed hologram in a single layer, lamination steps can be eliminated when arranging the master holograms on top of each other.In this way, errors associated with uneven deformation of the layers can be avoided, which in some cases leads to the preference of multiplexed master holograms over stacked master holograms. On the other hand, despite their somewhat better positioning accuracy, multiplexed holograms have a lower efficiency in diffracting radiation compared to stacked holograms.

[0014] A polychromatic holographic element can also comprise multiple holograms arranged one on top of the other in a stack. For example, a holographic element can comprise a plurality of superimposed monochromatic holograms that were recorded separately and combined into a stack. This allows the use of light-sensitive materials specifically designed for a particular wavelength or color channel, improving the quality of the hologram.

[0015] Such holographic elements are used in many areas, such as in transparent displays (e.g. in shop windows, refrigerated cabinets, vehicle windows), for lighting applications such as information or warning signals in glass surfaces, and light-sensitive detection systems, for example for interior surveillance (eye tracking in vehicles or presence status tracking of people indoors).

[0016] For example, DE102021116146A1 discloses a polychromatic hologram comprising six layers in a single stack. The layers are configured for different wavelengths. Three upper layers can form a first holographic element configured to convert an upward spherical wavefront into a downward plane wavefront by reflecting light from the blue, green, and red parts of the electromagnetic spectrum at predetermined angles. Three lower layers can form a second holographic element configured to reflect the downward plane wavefront back up to create a plane wavefront at a predetermined angle. In this way, the layers of the two holographic elements can function like a combination of a convex and a plane mirror.Advantageously, by arranging two holographic elements arranged directly one behind the other and at least partially reflective, a high refractive power can be achieved, while at the same time providing high image quality and a compact structure.

[0017] However, precise positioning of the holographic layers relative to each other is necessary to avoid unwanted filter effects and ensure optical performance. For multilayer holograms, it is crucial for the quality of the produced HOE that the superimposed holograms in a stack are correctly positioned relative to each other. Depending on the complexity of the HOE, the number of layers in such a stack can increase, which poses a significant challenge during the alignment steps of its production.

[0018] In an exemplary manufacturing process, a single, photosensitive composite web passes through various stations of a replication process, with replication occurring at each station for different master composites configured for a specific color channel. The composite web may comprise a photosensitive layer into which a master hologram of a color channel is replicated at each station. To achieve perfect positioning of the holograms replicated in the composite web, the flowing composite web must be braked at a precise position at each work station. Due to the deformable nature of the composite webs, it is extremely difficult to do this with a high degree of repeatability. This introduces alignment errors into the polychromatic hologram that exceed any alignment errors of the master composites used for replication.

[0019] Alternatively, a composite web can be exposed at a single workstation where a master composite is provided. Exposure can occur simultaneously or sequentially for each required wavelength. The flowing composite web only needs to be slowed down once during exposure, which reduces the risk of errors due to inaccurate positioning and / or deformation. However, errors in the relative positioning of the master hologram layers are reproduced in the composite web. For example, the layers for a particular color channel in a master composite may be twisted or offset during the exposure or integration process, which has a detrimental effect on the optical function, particularly of complex HOEs. The current state of the art does not currently offer any solutions for correcting positioning errors in the master composite once it has been created.Instead, these errors are reproduced in the copied holograms.

[0020] Another alternative is to produce each layer of a HOE master composite in a respective composite web with a single layer of photosensitive material and then combine the individual layers of the respective composite web into a stack. This avoids reproducing the positioning errors of the master composite. However, it also introduces new errors. Due to technical limitations, the placement, lamination, and bonding of the layers are carried out within tolerances, which also accumulate when the steps are repeated to create a stack with two, three, four, or more layers. In addition, adhesive layers may be required between the individual holograms to create the layer stack. This can increase the overall thickness of the layer stack, making it more difficult to embed the HOE in a component.JPH11272153A discloses the use of positioning marks to align different layers of a hologram stack. According to this document, a multilayer hologram is produced from a plurality of layers of light-sensitive material. Holograms with different properties are recorded in each layer of light-sensitive material, and positioning marks are holographically recorded in each of the multiple hologram layers. The positioning marks are then used to align the layers on a substrate and laminate them together.

[0021] On the one hand, this is complex. Furthermore, the process of laminating the layers itself can lead to alignment errors, e.g., due to varying degrees of deformation of the layers. Furthermore, the number of layers required to form the polychromatic hologram is high, and a method for changing the layer structure of the product compared to the master composite(s) used is unknown.

[0022] Depending on the intended use of the polychromatic hologram, it may be desirable to vary not only its positioning tolerances but also its thickness relative to the master composite. For example, in applications with a high risk of wear, it may be desirable to reduce the number of layers of the polychromatic hologram that could detach from each other. Reducing the overall thickness of the polychromatic hologram compared to the master composite may also be desirable, e.g., when embedding the polychromatic hologram in very thin products such as a holographic contact lens. It may therefore be advantageous to produce a polychromatic hologram with a different layer structure or overall thickness and improved positioning accuracy compared to the master composite.

[0023] Another approach to improving the positioning tolerances of a replicated polychromatic hologram could be to choose a master composite with a lower risk of positioning errors, e.g., by multiplexing all master holograms into a single layer. This also advantageously allows for lower overall thicknesses for a replication composite by replicating the master holograms as a multiplex in a single layer of the replication composite. However, such a multiplexed hologram may suffer from lower efficiency compared to a multilayer hologram. Therefore, it would be desirable to provide a technical solution that, depending on the desired application, ensures the required efficiency of the replicated polychromatic hologram as well as its overall thickness while simultaneously minimizing positioning tolerances.

[0024] Master composites are also susceptible to other defects and quality issues that arise during their manufacturing or service life. For example, a multiplexed hologram or various monochromatic master holograms within the master composite may swell or shrink due to their manufacturing method. This can shift the actual wavelength or angle at which the master hologram is most efficiently exposed. The shift is often wavelength-dependent. For example, a red channel in a multiplexed hologram or a red master hologram layer may experience a greater shift in optimal exposure parameters than a green channel or a green master hologram layer. If all channels of the master composite are replicated simultaneously, the replication parameters (e.g., the exposure angle of an RGB laser) can be shifted equally for all channels.However, this is not ideal, as the different channels can exhibit varying deviations from their target parameters. Copying such a master hologram often leads to inefficiencies and lower quality of the replicated hologram. Therefore, there is a need for a technique that can improve the efficiency and quality of a reproduced hologram compared to the master hologram.

[0025] There is therefore a need for alternative methods that can produce polychromatic holograms with a high degree of positional accuracy.

[0026] DE 10 2010 014 305 A1 discloses a method for producing copies of a volume reflection hologram. For this purpose, a holographic film is laminated over a drum with at least two (polygon) master surfaces, onto which it is brought into contact with at least one master hologram and exposed. One or more master surfaces can be laser-exposed simultaneously. The drum is rotated evenly or stepwise during exposure. This is intended to increase productivity even in the production of large-area reflection holograms. A use of the method for producing polychromatic holograms is not disclosed.

[0027] Object of the invention

[0028] The object of the invention is to provide a method that enables the replication of a polychromatic hologram without the disadvantages of the prior art. In particular, it was an object of the invention to provide a method for replicating a polychromatic hologram in which multiple color channels or patterns with different wavelengths can be positioned relative to one another in a holographic element using simple means, repeatably, and with high precision. Furthermore, it was an object of the invention to vary, and in particular to improve, the properties of a replicated polychromatic hologram compared to the properties of one or more master composites.

[0029] Summary of the invention

[0030] The object is achieved by the features of the independent claims. Advantageous embodiments of the invention are described in the dependent claims. In a first aspect, the invention relates to a method for replicating a polychromatic hologram composite, comprising the following steps: a. providing a first master hologram designed for a first wavelength range and a second master hologram designed for a second wavelength range, b. providing a replication composite with a first light-sensitive layer in / on a replication substrate c. exposing the first master hologram to obtain a first replicated hologram in the first light-sensitive layer by means of radiation of the first wavelength range, d. fixing the first replicated hologram in the first light-sensitive layer, e.Applying a second light-sensitive layer to the first light-sensitive layer, f. Exposing the second master hologram to obtain a second replicated hologram in the second light-sensitive layer using radiation of the second wavelength range, g. Fixing the second replicated hologram in the second light-sensitive layer.

[0031] The application of a second light-sensitive layer to the first light-sensitive layer after the first light-sensitive layer has been exposed and fixed enables a step-by-step buildup of a polychromatic hologram during the replication process. This step-by-step buildup allows the properties of the replicated polychromatic hologram to be varied, in particular improved, compared to the properties of the master holograms. Each layer of the replication composite can, in particular, advantageously be exposed separately with different parameters without affecting a previously exposed layer. Exposure parameters can therefore vary between the layers. A varying parameter can, for example, be a wavelength of the exposure radiation. Each light-sensitive layer of the replication composite can thus comprise a diffraction structure that deflects radiation of a different wavelength range.In this way, different diffraction structures with different wavelength characteristics can be stacked on top of one another under optimal exposure conditions. This enables the creation of multicolor holographic images, especially high-quality full-color images. Furthermore, light-redirecting functions can be ensured for large ranges of the electromagnetic spectrum, for example, for the redirection of light across the entire visible spectrum.

[0032] Varying the exposure parameters between the light-sensitive layers can also serve to compensate for errors or inefficiencies in different master holograms or color channels of a master composite. For example, a positioning error in one channel or a master hologram of a master composite, as described below, can be compensated for in one light-sensitive layer during exposure without affecting the other layers of the replication composite. Thus, the replication composite can be essentially free of the known positioning error of the master composite. In particular, the stepwise construction of the replication composite allows the master composite to be moved slightly and precisely between exposure steps so that the second and subsequent holograms are positioned exactly over the first exposed hologram.

[0033] The process according to the invention is an advantageous alternative to known processes in which the individual holograms are exposed separately and later combined. In particular, the process according to the invention eliminates the need for subsequent stacking and lamination of the various layers after they have been individually exposed. Alignment errors that typically arise from subsequent stacking and lamination are avoided.

[0034] The invention also takes advantage of the fact that new layers of photosensitive material can be applied to one another with a larger positional tolerance than separately manufactured hologram layers. This is because these layers have not yet been exposed to holograms and are largely uniform in their optical properties. The positioning of new photosensitive layers (such as the second and any subsequent photosensitive layers) relative to an already exposed and fixed layer is not critical. It can be subject to much larger tolerances than the application of one exposed hologram layer to another exposed hologram layer. The invention thus enables the use of rapid, cost-effective means to apply the second photosensitive layer to the first photosensitive layer.

[0035] By sequentially applying and exposing the second (and optionally further) light-sensitive layers, each new layer of the polychromatic hologram can be exposed with extremely precise alignment relative to a previously exposed layer. For example, the first and second master holograms are located in different workstations, i.e., spatially separated from each other. The first and second master holograms can be placed and fixed in position in the replication system in such a way that an ideal alignment of the first and second holograms is achieved in the replication composite when it is placed under the respective master hologram. Unpredictable deformation or displacement of the light-sensitive material, which often occurs during lamination, can be avoided.

[0036] Alternatively or additionally, the position of a second master hologram can be adjusted during exposure step (f) such that it corresponds to the position of an already exposed first master hologram. The second master hologram can be slightly rotated and / or translated to align it precisely with the actual position of the first hologram. The adjustment of the position of the second master hologram can preferably be carried out when the second master hologram is present in a stacked structure with the first master hologram in a composite by rotating and / or translating the entire master composite. The adjustment can also be carried out when the second master hologram is present in a separate master composite and / or a separate exposure station.This adjustment of the position of the second master hologram can improve the alignment of the holograms in the replica composite without causing the material to deform or shift, as often occurs during lamination. In all cases, the first and second holograms can be aligned and exposed with very tight tolerances. This avoids the introduction of alignment errors when stacking the holograms. Furthermore, the polychromatic hologram can be manufactured with tighter positional tolerances than a master composite.

[0037] Using the method according to the invention, an alignment error of the master composite can be easily corrected during replication into the replication composite. Since the master composite is generally robust, it can be rotated or translated as desired with high precision. Thus, the master composite can be moved between steps c and e to compensate for an alignment error between the first and second master holograms. The replication composite can thus advantageously have a tighter tolerance than the master composite.

[0038] To replicate the two master holograms in the replication composite, the first and second master holograms are preferably present in a single master composite. In this variant, the exposure of the first and second master holograms preferably takes place in the same workstation, so that movement of the replication composite between exposure steps can be avoided. The first and second master holograms are preferably stacked on top of one another. Likewise, the first and second master holograms can be present in a single layer as a multiplex. By constructing the replication composite step by step in this arrangement, each light-sensitive layer can advantageously be exposed with different exposure parameters. This means that the first light-sensitive layer can be exposed with first exposure parameters such as wavelength, exposure angle, and / or exposure intensity.After a first hologram has been fixed in the first photosensitive layer, the second photosensitive layer can be applied and exposed using different exposure parameters. For example, the second photosensitive layer comprises a different photosensitive material and / or a different thickness than the first photosensitive layer. The second photosensitive layer can be exposed using a different wavelength, exposure intensity, and / or a different exposure angle. The selection of a different exposure parameter can depend on the type of master hologram (transmission hologram or reflection hologram), its design for a specific wavelength range, its efficiency, its alignment, its degradation, and / or the wavelength-dependent radiation sensitivity of the photosensitive material.

[0039] Changing an exposure parameter is particularly useful if the master composite has experienced wavelength-dependent shrinkage / swelling. The wavelength-dependent shrinkage in one channel of the master composite can advantageously be compensated for independently of the other channels in a photosensitive layer. The wavelength range and / or the irradiation angle at which each photosensitive layer of the replication composite is exposed can therefore be adjusted according to the relevant degree of shrinkage. This allows exposure to occur with high efficiency despite a loss of quality in the master composite.

[0040] This can be achieved by exposing the light-sensitive layer to a slightly different exposure wavelength—preferably up to 50 nm, in particular up to 25 nm. The exposure wavelength can deviate from a theoretical target exposure wavelength of the currently exposed (second) master hologram or from the target exposure wavelength of the already exposed first (or further) master hologram. A deviation of the exposure wavelength of the second master hologram from the exposure wavelength of the first master hologram can also occur and is preferably greater than the deviation required to compensate for shrinkage / swelling.

[0041] Shrinkage (or swelling) can also change the optimal exposure angle of a master hologram depending on the wavelength. The exposure angle can therefore also deviate from a target exposure angle of the respective master hologram in order to increase the exposure efficiency for a specific light-sensitive layer. This can compensate for the efficiency loss that occurs due to degradation of the master hologram. This deviation in the exposure angle is preferably up to 3°, in particular up to 1°. Furthermore, the exposure angle of the second master hologram can deviate from the exposure angle of an already exposed master hologram. In such a case, the deviation can be greater and enable the visibility of different holographic patterns from different viewing angles. Other layers of the replication composite do not have to be affected.Alternatively or additionally, the exposure intensity can be adjusted between exposure steps, in particular to maintain an optical balance between the different channels.

[0042] By exposing the replication composite with a master composite comprising more than one master hologram (in a multiplex or in multiple layers), the replication composite does not need to be moved between exposure steps. This allows the second photosensitive layer to be applied to the first photosensitive layer without separating or moving the replication composite from the master composite. Instead, the second photosensitive layer can be applied in situ at the exposure station. Since there is no need to move the replication composite from one exposure station to a coating or further exposure station, the replication composite does not need to be precisely braked to determine its longitudinal position. The risk of a longitudinal positioning error of the replication composite is eliminated. Positioning reliability is further increased.

[0043] In order to replicate the two master holograms in the replication assembly according to a further preferred variant of the method, the replication assembly with the first replicated hologram can be moved from a workstation comprising the first master hologram to a further workstation comprising the second master hologram. The movement of the replication assembly can occur with very tight tolerances in a longitudinal direction and with essentially no rotation or displacement in the transverse direction. The former can be achieved by a precise braking mechanism, the latter by the mechanical design of a transport unit itself, such as transport rollers or a conveyor belt with a precisely adjusted width. Precise adaptation of the width of the transport rollers to the width of the replication assembly can preferably mechanically prevent rotation or displacement of the replication assembly in the transverse direction.Subsequently, steps e to g preferably follow. The second master hologram can preferably remain fixed in its position during this process. The position of the second replicated hologram in the second light-sensitive layer is preferably free from rotation or translation in a transverse direction, particularly with respect to the first replicated hologram.

[0044] The polychromatic hologram can therefore have tighter tolerances than a polychromatic master composite comprising a stack of master holograms. The alignment properties of the replica composite, particularly the rotational alignment and transverse position, can instead be improved compared to the master holograms. Further exposure parameters can also be changed between exposure steps for the first, second, and subsequent light-sensitive layers, particularly to increase the quality of the polychromatic hologram.

[0045] The invention also benefits from the adhesive properties of photopolymer layers on carrier layers. This can lead to particularly thin, multilayer polychromatic holograms. With respect to a prior art multilayer polychromatic hologram in which three separately exposed holograms are stacked together, each hologram of the stack typically comprises a photosensitive material enclosed between two carrier layers. A further adhesive layer is added between the carrier layers of the first and second hologram and between the carrier layers of the second and third hologram to form the stack. A prior art layered structure may, for example, comprise: polycarbonate - photopolymer 1 with 1° hologram - polycarbonate - adhesive - polycarbonate - photopolymer 2 with 2° hologram - polycarbonate - adhesive - polycarbonate - photopolymer 3 with 3° hologram - polycarbonate.A total of 11 layers are required to form the stack. This results in a greater thickness, which can complicate discrete embedding in a product. On the other hand, it has been discovered that various light-sensitive materials can be applied to a transparent carrier film in such a way that they remain stable throughout their entire lifetime. Additional carrier layers and adhesive layers between the holograms can be omitted. In this way, a simplified, thinner layer structure can be created. A polychromatic hologram with three channels according to the present invention can, for example, be constructed as follows: polycarbonate - photopolymer 1 - polycarbonate - photopolymer 2 - polycarbonate - photopolymer 3 - polycarbonate. The 11-layer structure can be reduced to a 7-layer structure.

[0046] For the purposes of the invention, a "method for replicating a hologram" or a "replication method" is preferably a method in which the diffraction pattern of an object, in particular a master hologram, is recorded in a light-sensitive material. This comprises at least one exposure of the respective master hologram, but may also include further preferred steps such as fixing or cutting.

[0047] A "master hologram" within the meaning of the invention is preferably a holographic-optical element comprising at least one hologram to be replicated. The master hologram is designed for an optical function (e.g., diffraction, reflection, transmission, and / or refraction) for one or a plurality of wavelengths within a wavelength range. The master hologram can, for example, be a diffractive optical element (DOE). Diffractive optical elements (DOEs) utilize a surface relief profile with a microstructure for their optical function. Alternatively, the microstructure can also be present in the volume of the element in the form of a local difference in the refractive index. Such a master hologram is considered a so-called "volume hologram." The light transmitted by a DOE can be converted into almost any desired distribution through diffraction and subsequent propagation.This can be an image, a logo, text, a light refraction pattern, or something similar. The master hologram can also be a technical hologram, such as a Bragg mirror, a diffuser, or a hologram acting as a lens.

[0048] A "design of a master hologram for a wavelength range" preferably means that the diffraction structure of the master hologram is configured for the diffraction of electromagnetic radiation having a wavelength in the wavelength range. In other words, the first master hologram is preferably wavelength-selective for a first wavelength range, while the second master hologram is wavelength-selective for a second wavelength range. Wavelength selectivity means, in particular, that the diffraction conditions provided by the first master hologram are preferably only for light of a first wavelength range. Radiation of other wavelengths is preferably not diffracted. The same applies to a wavelength selectivity of the second master hologram, according to which diffraction should occur selectively for radiation of a wavelength in the second wavelength range.

[0049] According to the invention, the first and second wavelength ranges are not identical. In preferred embodiments, the first and second wavelength ranges may represent disjoint ranges and have essentially no intersections. This may be the case, for example, if the first and second wavelength ranges correspond to different colors. For example, a first wavelength range may correspond to one color (e.g., blue, red, or green), while the second wavelength range corresponds to a different color.

[0050] For the purposes of the invention, a “wavelength range” may essentially comprise light or radiation of one wavelength, for example the wavelength emitted by a monochromatic laser.

[0051] In the case of a reflection hologram, the hologram can be configured such that electromagnetic rays in the wavelength range are diffracted, so that a first-order diffracted beam travels back into a replication compound. The first-order diffracted beam can interfere with the reference beam in the replication compound. Radiation with wavelengths outside the wavelength range can preferably be transmitted without diffraction. In the case of a transmission hologram, the hologram can be configured such that electromagnetic rays in the wavelength range are diffracted, so that a diffracted beam interferes with a reference beam in the replication compound. Electromagnetic rays with wavelengths outside the wavelength range can preferably be transmitted undiffracted. The master hologram thus preferably diffractes the radiation of the wavelength for which it is designed.

[0052] A "master composite" within the meaning of the invention is preferably a multilayer composite comprising at least one master hologram. The master composite preferably comprises at least a first master hologram and a second master hologram in a layered structure. The master composite can preferably comprise further layers, such as one or more covers and / or a master substrate, so that the master hologram (or master holograms) are preferably present between the master substrate and the cover. The master holograms are preferably laminated to a surface of the master substrate. The master composite is preferably rigid. The rigidity of the master composite can be ensured by a master substrate. Preferably, all layers of the master composite are firmly connected to one another. The "master composite" can be arranged in a master element, wherein in preferred forms the master element comprises the master composite and a base substrate.Preferably, the master composite can move with respect to the base substrate.

[0053] A "master element" preferably comprises at least one master hologram and supports the creation of a mechanical and / or optical contact between the respective master hologram and a light-sensitive layer or a replication composite without damaging the master hologram. The master element preferably comprises a master substrate on or in which at least one master hologram is present. The master element preferably further comprises a base substrate, wherein the master substrate is movably mounted with respect to the base substrate. The base substrate is preferably aligned for contact with the replication composite. The master element preferably further comprises an alignment module for moving the master substrate (and thus also the master hologram) with respect to the base substrate.

[0054] The "master substrate" is preferably a three-dimensional unit comprising a master hologram in a shape that facilitates its handling and mobility. The shape of the master substrate is fundamentally unlimited. In particular, the master hologram is enclosed by the master substrate in such a fixed position that a movement of the master substrate directly leads to a corresponding movement of the master hologram. The master substrate can have a prismatic, in particular a cylindrical, shape. This can be particularly advantageous if the master substrate carries only one master hologram, wherein the exposure steps of the method are carried out with different master composites. It can also be preferred for the master substrate to have the shape of a cuboid or a plate, in particular if the master substrate carries multiple master holograms, wherein multiple exposure steps of the method are carried out with the same master composite.Preferably, the master substrate has a length and width approximately equal to that of the master hologram. The master substrate is preferably at least twice, preferably five times, and particularly preferably at least twenty times the height of the master hologram. The master substrate preferably has a regular shape that allows for a mosaic-like or linear arrangement.

[0055] The master substrate is preferably a transparent plate, preferably made of optical glass or plastic. The master holograms can be laminated to a surface of the master substrate to form a master composite. In some preferred embodiments, the master composite can further comprise a transparent top cover for protecting one or both master holograms, which is / are present between the cover and the master substrate. Preferably, the top cover is also transparent. The top cover can be, for example, a transparent film or a glass layer.

[0056] For the purposes of the invention, the term "transparent" or "transparency" preferably refers to a property of a material whereby it is substantially permeable to light. A transparent material within the meaning of the invention is preferably transmissive for at least part of the electromagnetic spectrum, preferably with a wavelength between 200 nm and 25 pm, particularly preferably between 400 nm and 780 nm. A transparent material, for example a transparent master substrate or a transparent cover, is particularly preferably permeable to radiation within a wavelength range with which the master hologram is exposed. A transparent material can also be colored to select radiation of one or more specific wavelengths.

[0057] It is preferred that the surface or cover of the master composite comprises glass, PC, TAC, or PMMA. The surface material can be in the form of a film or plate to protect the master hologram. However, the surface or cover material can also be the material of the master substrate itself and, for example, have a cuboid or cylindrical shape.

[0058] In preferred embodiments, the master element comprises a master composite and a base substrate, wherein the master composite and the base substrate are mounted so as to be movable relative to one another. This solution allows one substrate of the master element to be held stationary while another substrate is rotated or translated. Preferably, the base substrate is held stationary while the master substrate (and thus the master holograms) is moved. In this way, the replication composite can be brought into constant contact with a surface of the master element without frictional forces or deformations occurring between exposure steps due to relative movement at an interface. Direct contact of the replication composite with a movable mechanical part of the master element (the master composite) is avoided, thus also eliminating the risk of mechanical deformation of the replication composite.At the same time, the master assembly can be moved freely relative to the base substrate (and thus also the replication assembly) to compensate for any positioning error in the master assembly. Furthermore, the replication assembly does not need to be kept at a distance from the master element that could lead to a loss of efficiency in the exposure process. Instead, the mechanical contact between the replication assembly and the base substrate can ensure optimal optical contact, thus minimizing optical losses at the interface between the replication assembly and the master element.

[0059] A "base substrate" within the meaning of the invention is preferably a three-dimensional unit designed for mechanical contact with a replication composite. The base substrate is preferably rigid so that one or more layers can be laminated onto it. The base substrate is preferably mounted stationary, with a master composite preferably being mounted movably with respect to the base substrate. The base substrate preferably has analogous optical and mechanical properties to those of the master substrate. The base substrate is in particular transparent, preferably made of optical glass or plastic. The shape and dimensions of the base substrate can be analogous to those of the master composite and preferably exceed them, so that the master composite is still completely covered by the base substrate in all rotational and translational positions.For example, the length and / or width of the base substrate can be at least 110%, preferably at least 120%, even better at least 130% of the length and / or width of the master composite. A "replication composite" within the meaning of the invention is preferably a multilayer material comprising at least one photosensitive layer. The photosensitive layer preferably comprises a photosensitive material, such as a silver halide, a dichroic gelatin, a photoresist, a photopolymer, a photochromic material, a photothermoplastic, LiNbCh, Bii2SiO2O, CCD, or combinations thereof. The photosensitive layer can be sensitive to electromagnetic radiation in a broad wavelength range. For example, the photosensitive layer can be sensitive to electromagnetic radiation of both the first wavelength range and the second wavelength range.Alternatively, a first photosensitive layer can be sensitive exclusively to electromagnetic radiation in the first wavelength range, and a second photosensitive layer can be sensitive exclusively to electromagnetic radiation in the second wavelength range. Any number of photosensitive layers can be provided, for example two, three, or more, with the sensitivities of the layers overlapping or not overlapping in the wavelength ranges as required. The replication composite preferably comprises at least one, preferably two outer carrier films, the carrier films preferably being transparent to electromagnetic radiation of all wavelengths with which the replication composite is to be irradiated. The photosensitive layers can be in the form of a composite web. In preferred forms, the replication composite can also be in the form of a composite web.The replication composite may comprise a replication substrate which is preferably in contact with the light-sensitive layers directly or with further intermediate layers.

[0060] The application of a second light-sensitive layer to the first light-sensitive layer of the replication composite preferably results in a layered structure of the light-sensitive layers on top of or above one another in the replication composite. After exposure and fixation, the replicated first hologram and the replicated second hologram are preferably also arranged one above the other in a layered structure. In preferred embodiments, further light-sensitive layers can be applied to the first two light-sensitive layers or hologram layers.

[0061] The light-sensitive layer may lose its light-sensitive properties during the process according to the invention, e.g., due to fixation. For the sake of simplicity, the layer in question in the replication composite is still referred to as a light-sensitive layer even if it no longer reacts to incident light rays. Those skilled in the art will know which layers are meant by this, especially since they continue to be based on the same light-sensitive material. In some passages, the light-sensitive layer is referred to as a holographic layer or hologram layer after it has been exposed.

[0062] In preferred embodiments of the invention, the exposed replication composite is pre-fixed after exposure before the exposed replication composite is moved. The pre-fixing can stabilize the exposed photosensitive layers sufficiently to bring them to a further treatment station, in particular a fixing station, without affecting the already replicated hologram. This is particularly advantageous for replication composites comprising liquid or soft photosensitive layers. It can also be preferred that the replicated polychromatic hologram comprising any number of layers is completely fixed after all exposure steps. The complete fixing can take place in situ, in particular in an exposure station, without moving the replicated polychromatic hologram. Alternatively or additionally, the complete fixing can take place in a downstream fixing station.Such fixation can be performed on a stationary, replicated polychromatic hologram or while the replicated polychromatic hologram is transported through the fixation station. The latter can allow for uniform dosing of UV irradiation and / or heat across the replicated polychromatic hologram while using lower-power devices.

[0063] In the following preferred embodiments, "fixing" preferably refers to a complete fixation, a pre-fixation, or a final step of fixing a photosensitive material that has already been pre-fixed.

[0064] For the purposes of the invention, "fixing" is preferably a treatment of a light-sensitive material to reduce its sensitivity to further exposure by further electromagnetic irradiation and / or mechanical influences. Fixing can further be configured to adapt the material properties of the light-sensitive material, in particular by reducing its viscosity and / or by converting the material into a semi-solid or solid form. It may be preferred that fixing is applied to an already exposed light-sensitive layer of a replication composite in order to stabilize the light-sensitive material and prevent further exposure of grids. The same means as for full fixing can be used for pre-fixing, in particular UV irradiation and heat treatment.It may be preferable that the process parameters used for fixation, such as the intensity of UV radiation or the temperature of a heater, are adjusted to achieve the desired mechanical properties and / or the desired lower light sensitivity.

[0065] For the purposes of the invention, the replication composite preferably becomes a polychromatic hologram if the replication composite comprises two or more holograms designed for different wavelength ranges. The presence of a replication substrate in the polychromatic hologram is optional.

[0066] For the purposes of the invention, a "replication substrate" is preferably a component which, during exposure, is preferably located between the one or more photosensitive layers and the master composite. The replication substrate preferably provides optical contact between the master composite and the photosensitive layers, wherein the replication substrate preferably also protects the photosensitive layers from mechanical damage. In a preferred embodiment of the invention, the replication substrate is a further film-like layer, such as a protective layer, flexible base, or carrier layer. It can be used in the handling of the replication composite, e.g., to bring it to a master element and integrate it into a final product, wherein the replication substrate can be removed during the integration process.In a further preferred embodiment of the invention, the replication substrate is rigid, wherein a section of a composite web comprising one or more photosensitive layers is laminated to the replication substrate to create a stable replication composite. Such a replication substrate can have similar properties to the master substrate and / or the base substrate and can serve as an alternative to the base substrate. Preferably, the rigid replication substrate is in the form of a plate. An advantage of this embodiment is that a rigid replication substrate can be transported with the remaining parts of the replication composite to further processing stations of a manufacturing process. This may be preferred in cases where the production of a series of polychromatic holograms, each constructed on a rigid replication substrate, is desirable for the subsequent processing of the polychromatic hologram.For example, a rigid replication substrate can be used to precisely position multiple polychromatic holograms on top of each other and encapsulate them between the substrates. The flexural strength of the replication substrate reduces the risk of unwanted deformation or shifting when stacking multiple polychromatic holograms on top of each other. The positioning errors typically caused by foil lamination can be avoided.

[0067] A “composite web” within the meaning of the invention is preferably a composite material with a length that is at least twice, preferably at least five times, and even more preferably at least twenty times its width. The thickness of the composite web is preferably adjusted to have a certain flexibility so that it can be provided, for example, as a roll. Preferably, the composite web has a thickness of up to 300 μm. The composite web comprises a photosensitive material. Preferably, the composite web encloses the photosensitive material between two transparent carrier films that have a similar refractive index to the photosensitive material. Preferably, the refractive index of the carrier films and the photosensitive material is between 1.4 and 1.6. The photosensitive material can be, for example, a photosensitive photopolymer or a dichroic gelatin.The light-sensitive material can be light-sensitive to the entire visible spectrum or wavelength-selective.

[0068] In the context of the invention, "exposure" is preferably understood to mean the targeted directing of electromagnetic radiation onto a correspondingly sensitive surface, preferably to form a hologram. Various methods for exposing a hologram are known, including transmissive or reflective techniques for producing volume holograms.

[0069] A volume hologram is preferably written into a sensitive layer by the interference of two light beams (a so-called reference beam and an object beam). Preferably, a volume hologram is written into the replication composite. This can preferably be done using a transmission or reflection technique. Interference of object and reference beams within the hologram volume preferably creates a sequence of Bragg planes. A volume hologram therefore preferably has a non-negligible extension in the propagation direction of the light beams, whereby the Bragg condition applies during reconstruction on a volume hologram. For this reason, volume holograms exhibit wavelength and / or angular selectivity. The ability of volume holograms to store multiple images simultaneously enables, among other things, the production of colored holograms.Light sources that emit the three primary colors blue, green, and red can be used to record holograms. These three beams preferably simultaneously illuminate a portion of the replicated image at equal angles. After exposure, three holograms are stored simultaneously in the volume hologram. To reproduce the polychromatic hologram, it can be exploited that each partial hologram can be reconstructed using only the color with which it was recorded. Thus, the three reconstructed color separations overlap to form a true-to-original color image, provided the color components are correctly weighted.

[0070] Exposure can preferably be carried out by an exposure module which has one or more light sources provided for this purpose. The light source is also referred to as a "radiation source" since non-visible regions of the electromagnetic spectrum can also be used to produce the holograms. For this purpose, the light source(s) or radiation source(s) preferably emit electromagnetic radiation in a first and / or second wavelength range. A coherent light beam is preferably emitted from the light source. Coherence preferably refers to the property of optical waves according to which there is a fixed phase relationship between two wave trains. As a result of the fixed phase relationship between the two wave trains, spatially stable interference patterns can arise. With regard to coherence, a distinction can be made between temporal and spatial coherence.Spatial coherence preferably represents a measure of a fixed phase relationship between wave trains perpendicular to the propagation direction and is present, for example, for parallel light beams. Temporal coherence preferably represents a fixed phase relationship between wave trains along the propagation direction and is present in particular for narrowband, preferably monochromatic light beams.

[0071] The coherence length preferably refers to the maximum path length or travel time difference between two light beams from a starting point, so that a (spatially and temporally) stable interference pattern is still created when they superpose. The coherence time preferably refers to the time it takes for the light to travel a coherence length.

[0072] In preferred embodiments, the light source comprises a laser. Particularly preferably, it is a narrowband, preferably monochromatic laser with a preferred wavelength in the visible range (preferably 400 nm to 780 nm). Non-exhaustive examples include solid-state lasers, preferably semiconductor lasers or laser diodes, gas lasers, or dye lasers. Lasers can be selected to emit light of a specific wavelength or wavelength range. This can be achieved by selecting a laser made of a suitable material. Examples include ruby ​​lasers, He-Ne lasers, Ar + -Laser, Kr + -Laser, He-Cd laser and / or Nd 3+YAG lasers can be used. These or other laser types can be combined with an optical parametric oscillator to generate coherent beams of different wavelengths. Lasers with different wavelengths can also be combined, for example, to create an RGB laser.

[0073] Various laser types, particularly solid-state lasers, can be combined with an optical parametric oscillator to generate coherent beams of different wavelengths as a tunable system. The optical parametric oscillator preferably comprises an optical resonator and at least one nonlinear optical crystal. Systems with a plurality of converter crystals can be used, in particular, using three-wave mixing (f_pumpe = f_signal + f_dler). By varying the frequency of f_signal and / or f_dler, laser wavelengths can be generated in a very broad wavelength range. This includes, in particular, the entire visible and infrared ranges of the electromagnetic spectrum.

[0074] Other light sources, preferably coherent light sources, can also be used. Narrowband light sources, preferably monochromatic light sources, such as light-emitting diodes (LEDs), optionally in combination with monochromators, are preferred.

[0075] For replication with different wavelengths, in particular a first and second wavelength range, it is preferred to provide illumination radiation in the respective different wavelength ranges, e.g. in a red wavelength range (preferably 620 nm - 700 nm), a green wavelength range (preferably 500 nm - 560 nm) and / or a blue wavelength range (preferably 420 nm - 475 nm).

[0076] For example, a laser system with three monochromatic lasers or one polychromatic laser with a laser emission in the red, green or blue (RGB) range can be provided for this purpose.

[0077] In the context of the invention, "alignment of a master hologram" preferably means that the master hologram is moved from an actual position to a desired position. Preferably, the movement from the actual position to a desired position comprises a slight correction, in particular to compensate for a positioning error, and is therefore different from a step in which a master composite or master hologram is brought to a workstation. The alignment preferably comprises a translation in a transverse direction, a translation in a longitudinal direction, and / or a rotation in a plane comprising the transverse and longitudinal directions. The transverse and longitudinal directions are preferably orthogonal to one another in a plane comprising the master hologram and / or parallel to the replication composite. Preferably, the alignment movement is large enough to compensate for any errors in the positioning of the master hologram.For example, the translation in the longitudinal and / or transverse directions can be up to 1000 micrometers, preferably up to 100 micrometers, more preferably up to 20 micrometers, even more preferably up to 10 micrometers. The rotation is preferably up to 2°, preferably up to 1°, more preferably up to 0.5°.

[0078] A "longitudinal direction" within the meaning of the invention is preferably any direction in the plane formed by a surface of the master hologram in question. This is preferably a substantially horizontal plane. The longitudinal direction particularly preferably coincides with a direction in which a replication assembly moves to move into or out of an exposure station where exposure takes place.

[0079] A "transverse direction" within the meaning of the invention preferably runs orthogonally to the longitudinal direction in a plane formed by the surface of the master hologram in question. A "rotation" of the master hologram preferably also occurs in this plane.

[0080] For the purposes of the invention, a "polychromatic hologram" is preferably a hologram configured to diffract electromagnetic radiation of different wavelengths, wherein the different wavelengths preferably differ by at least 50 nm, more preferably by at least 100 nm, and even more preferably by at least 200 nm. Preferably, the polychromatic hologram may comprise a plurality of channels, each channel corresponding to a different wavelength and / or wavelength range. Each channel may be the result of replicating a master hologram configured for the respective wavelength or wavelength range. For example, the channels may correspond to different colors, such as red, green, and blue light.A color, in the sense of the invention, preferably means light of a specific wavelength range from the visible spectrum (380 nm to 780 nm) with a bandwidth of less than 50 nm, preferably less than 40 nm, less than 30 nm or less, with a maximum or peak at a central wavelength characteristic of the color. For blue light, for example, the central wavelength can be approximately 460 nm, while green light can have a central wavelength of approximately 530 nm or red light a central wavelength of approximately 630 nm. It can also be preferred that one or more of the channels correspond to electromagnetic radiation outside the visible spectrum, such as UV radiation or IR radiation. The various channels can be present in a polychromatic hologram in the form of a diffraction structure that is configured to emit electromagnetic radiation of the respective wavelength or wavelengths.of a particular wavelength range. The diffraction structures can be present in a single layer of the light-sensitive material or in different layers.

[0081] The presence of multiple diffraction structures designed for different wavelength ranges in the same layer is referred to as a "multiplex" within the meaning of the invention. In a "multiplex" hologram, different diffraction structures are preferably superimposed in one material, whereby the different diffraction structures are assigned to different (color) channels or are designed for different wavelength ranges. This means that in some embodiments, although the master composite comprises multiple master holograms in different layers, all or some of these can be replicated in the same light-sensitive layer of the replication composite. A second light-sensitive layer of the replication composite can be exposed with another master composite. However, the layer structure of the replication composite can alternatively reflect the layer structure of the master composite.

[0082] A “light-sensitive material” within the meaning of the invention is a material that reacts to radiation from a region of the electromagnetic spectrum with which the master hologram is exposed. The light-sensitive material preferably reacts to light from the visible region of the electromagnetic spectrum. The light-sensitive material particularly preferably reacts to the radiation by producing a local change in its refractive index. This can occur, for example, through local polymerization of monomers or shorter polymer chains, as in the case of a photopolymer. The light-sensitive material can lose its light-sensitive properties during the process according to the invention, e.g. through fixation. For the sake of simplicity, the material in question in the replication composite is still referred to as light-sensitive material even if it no longer reacts to incident light rays.

[0083] In a preferred embodiment of the invention, the method comprises the following further steps: a. applying a third light-sensitive layer to the second light-sensitive layer, b. providing a third master hologram designed for a third wavelength range, c. exposing the third master hologram to obtain a third replicated hologram in the third light-sensitive layer using light of the third wavelength range, d. fixing the third replicated hologram in the third light-sensitive layer.

[0084] In this case, a polychromatic hologram can be advantageously produced with a third replicated hologram or a third (color) channel in the replication composite, without the need to subsequently position three exposed holograms on top of each other. The resulting polychromatic hologram can display a sharp full-color image or another pattern from different regions of the electromagnetic spectrum.

[0085] The well-known alternative of producing the holograms separately and later stacking them on top of each other can result not only in a positioning error between the first and second holograms, but also in a further positioning error between the third hologram and the stack of the first and second holograms. These combined errors can significantly impair the quality of a generated full-color image and even render a functional hologram unusable for its intended purpose. For example, for a polychromatic hologram acting as a light-gathering lens or mirror, it is difficult to ensure that the convergence point is the same for all three wavelength ranges if there is a separate hologram for each wavelength range. By applying the third light-sensitive layer to the second hologram before its exposure, such sources of error can be avoided and the quality of the polychromatic hologram can be increased.As explained above, the positioning of another unexposed light-sensitive layer is much less critical than the positioning of an exposed hologram.

[0086] The use of a newly applied light-sensitive layer for the exposure of the third master hologram also makes it possible to expose the third master hologram with different parameters than the first and second master holograms and / or in a different material. For example, the third master hologram is exposed with a different wavelength range and / or different exposure angle. This enables the creation of a polychromatic hologram with a complex function.

[0087] Changing the exposure parameters can allow the exposure of different patterns and / or optical functions in a polychromatic hologram. For example, the different light-sensitive layers of the replication composite can be exposed from different angles, with the angles differing by at least 5°, preferably at least 10°. Thus, a reflection hologram can display different contents depending on the viewing angle. For example, it may be preferable for a first content to be visible from a left viewing angle and a second content to be visible from a right viewing angle. Changing the exposure angle between exposure steps can also be useful for polychromatic holograms in which all channels are intended to be visible from a single viewing angle. The third master hologram may have experienced shrinkage or swelling due to its manufacturing process.This can change the wavelength characteristics of the master hologram. The angle at which the third master hologram is most efficiently exposed may deviate from a target angle. By slightly adjusting the exposure angle from the target angle to an optimized angle, the third master hologram can be exposed with increased efficiency. A slight adjustment of the exposure angle is preferably less than 3°, in particular less than 2°. The other holograms can continue to be exposed at the target angle or at a separately optimized angle.

[0088] By exposing each of the first, second, and third master holograms in a separate layer in the replication composite, each of the produced holograms can have different properties that differ from those of the respective master holograms. For example, the different master holograms can be exposed at different intensities. The relative position of the third hologram with respect to the first and / or second hologram can differ from the relative position of the third master hologram with respect to the first and / or second master hologram. As explained in more detail below, errors in the position of the second, third, or further master holograms in the replication composite can also be corrected.

[0089] In a further preferred embodiment of the invention, a number of light-sensitive layers or holographic layers in the polychromatic hologram differs from a number of master hologram layers in a master composite or from a number of master holograms used in different master composites. In particular, a master composite can comprise two or more master holograms, which are replicated in one, two, or more layers of the replication composite. At the same time, preferably, all master holograms of the master composite are replicated in the replication composite. A deviation in the number of light-sensitive layers can be provided for the exposure of two or more master hologram layers into the same light-sensitive layer. This reduces the number of layers of the replication composite compared to the master composite.Alternatively or additionally, the number of light-sensitive layers can be varied by exposing diffraction structures of a single-layer multiplex hologram, which are designed for different wavelength ranges, to two or more light-sensitive layers. This increases the number of layers of the replication composite compared to the master composite. Using one or a combination of these techniques, the material structure and the total thickness of the polychromatic hologram can differ from the material structure or total thickness of the master composite. Depending on the application, this can advantageously ensure, for example, the required total thickness and / or efficiency of the replicated polychromatic hologram while simultaneously minimizing positioning tolerances.

[0090] In a preferred embodiment of the invention, the master composite comprises multiple layers of wavelength-selective photosensitive material. The structure of the polychromatic hologram, however, can be optimized for its intended use. In applications (or further processing steps) where wear may lead to delamination of layers or melting of an adhesive layer, it may be desirable, for example, to replicate the multiple master holograms of the master composite in a single photosensitive layer. This reduces the risk of the layers detaching from one another. Furthermore, the overall thickness of the product can be reduced, as the intermediate carrier layers or adhesive layers can be omitted. The resulting polychromatic hologram is particularly thin and robust, which facilitates its integration into a product.

[0091] In a further preferred embodiment of the invention, two or more master holograms are present as a multiplex hologram. The multiplex hologram preferably comprises a first and a second master hologram in the same layer. The first and second master holograms are designed in particular for different wavelength ranges, which preferably do not overlap with one another. The master holograms preferably comprise diffraction patterns that are present in the same material layer and diffract radiation of different wavelength ranges. Such a multiplex hologram can be particularly compact and advantageously dispenses with lamination steps for arranging the master holograms one above the other. However, compared to polychromatic stacks, multiplex holograms often have limited efficiency with regard to the desired diffraction of the exposure radiation.However, the multiplex hologram can advantageously be converted into a multilayer polychromatic hologram using the method according to the invention to increase efficiency. Thus, in step c—due to the design of the first master hologram for the first wavelength range—only the first master hologram of the multiplex hologram can be replicated in the first light-sensitive layer. The first master hologram can thus be replicated independently of the other master holograms of the multiplex hologram under appropriate, preferably monochromatic, exposure.

[0092] In step f, the second master hologram can be replicated into the second light-sensitive layer. Thus, the first hologram can be replicated separately from the second hologram. Furthermore, the first and second holograms can be replicated in different ways. For example, each of the first and second holograms can be replicated in a different light-sensitive material. The light-sensitive material can be specifically suited to capturing the features of the respective hologram, in particular for exposure to the respective wavelength range. This can improve the quality of each hologram of the polychromatic hologram compared to the multiplexed hologram.

[0093] The individual replication of the master holograms enables the achievement of higher efficiencies in each replicated hologram. This can be achieved, among other things, by a specific selection of the light-sensitive materials used, e.g., by choosing suitable photosensitizers for response to a specific wavelength range. This can advantageously result in an increase in the efficiency of the holograms in the individual light-sensitive layers compared to the corresponding diffraction structure of a multiplex hologram. The increase in efficiency can be an increase of 50%, 100%, 200%, or more (relative to the efficiency of the corresponding diffraction structure of a multiplex hologram).For example, a multiplexed master composite with 30% diffraction efficiency for each of the RGB color channels can be advantageously used to obtain a replication composite with a layer structure in which the respective replicated holograms in the various layers have an efficiency of 70% or more.

[0094] In a further preferred embodiment of the invention, the positions of the individual master holograms (or channels) within the multiplex master hologram are adjusted before an exposure step. Thus, smaller positional tolerances can be achieved in the multilayer polychromatic hologram than in the multiplex master hologram.

[0095] In a preferred embodiment of the invention, a subset of the master holograms in a multiplex hologram is replicated separately in individual layers. It may be advantageous for another subset of master holograms present in the same multiplex hologram not to be replicated or to be replicated within a single light-sensitive layer to form another multiplex hologram in the replication composite.

[0096] In further preferred embodiments of the invention, the master hologram stack comprises multiple master holograms. A subset of these master holograms can be replicated in a single light-sensitive layer of the replication stack to form a multiplex hologram, while another subset of the master holograms can be replicated in individual light-sensitive layers of the replication stack. The techniques of combining master holograms into a multiplex or dividing multiplex master holograms into individual layers can thus be combined as needed.

[0097] For example, it may be desirable to increase the efficiency of a polychromatic hologram produced from a master composite while ensuring a sufficiently low overall thickness for the application. In this example, the master composite comprises three or more master holograms. The multiplex hologram may, in particular, comprise a first master hologram designed for red light, a second master hologram designed for green light, and a third master hologram designed for blue light. For example, the application may require a particularly high efficiency of the third (blue) hologram to be replicated, while this is not the case for the other color channels (red and green).

[0098] The first (red) and second (green) master holograms can be replicated as multiplex holograms in a single light-sensitive layer of the replication composite to maintain a low overall thickness. However, to increase efficiency, the third (blue) master hologram can advantageously be replicated separately in another specialized light-sensitive layer of the replication composite.

[0099] The resulting polychromatic hologram can thus exhibit the required high efficiency for application in the respective color channels, while simultaneously ensuring the required low overall thickness. The method according to the invention thus allows for particularly flexible adaptation of the replication process depending on the desired application-side properties of the replicated holograms.

[0100] In a further preferred embodiment of the invention, the method comprises providing a third master hologram designed for a third wavelength range. The third master hologram can be copied into the second photosensitive layer to form a multiplex hologram therein, preferably consisting of the second hologram and a third hologram. Preferably, the second photosensitive layer is sensitive to light waves in both the second wavelength range and the third wavelength range. Step g of fixing the second photosensitive layer can then be carried out to fix both the second and the third hologram therein. In this way, a master composite comprising three master holograms in three separate layers can be converted into a two-layer polychromatic hologram.Alternatively, the third master hologram can also be replicated into the first light-sensitive layer, for example, so that the first light-sensitive layer comprises both a first and a third hologram. The second light-sensitive layer comprises a second hologram. With the two-layer polychromatic hologram, a particularly low thickness can be achieved in the product. This can be particularly useful if the polychromatic hologram is to be embedded inconspicuously, e.g., between the glass layers of a windshield.

[0101] In a further preferred embodiment of the invention, the first and / or second master hologram is / are provided in a master composite, wherein the same master composite or a master composite with an identical configuration is used to expose the first and second light-sensitive layers. Optionally, the exposure of the first and second light-sensitive layers can each be carried out with a master composite, wherein one master composite comprises the first master hologram and a different master composite comprises the second master hologram. By providing the first and second master hologram in the same master composite, the first and second holograms can advantageously be exposed in a single workstation. Movement of the replication composite between different exposure stations can be avoided, and the risk of a positioning error of the replication composite in the longitudinal direction can be eliminated.This allows both the first and second holograms to be exposed and fixed in one location to form a stable layer structure before it is moved. The risk of quality defects due to stray light or mechanical deformation of one of the layers is further reduced.

[0102] By providing the first and second master holograms in the same master composite, the master holograms remain in the same relative positions to each other. Positioning errors between the two master holograms may occur. However, since these errors are constant, they can advantageously always be compensated for in the same way. This simplifies the implementation and control of the process to create a polychromatic hologram with improved positional tolerances. Furthermore, by exposing the first and second photosensitive layers to the same master composite, the positional tolerances of the two holograms relative to each other can be kept small.Given a master composite with sufficiently small positional tolerances between the first and second master holograms, exposing the same master composite without moving the master composite and / or the replication composite can result in equally small positional tolerances of the two holograms in the replication composite. New positional errors, particularly in the longitudinal direction, are not introduced by omitting movement of the replication composite. To not only keep the positional tolerances small but even improve them, the master composite can be moved between exposure steps to compensate for any positional errors of the second master hologram. This allows the second master hologram to be positioned over the first hologram with particularly high precision before the second exposure takes place.

[0103] This advantageously results in a replication composite that not only has no additional tolerances due to the replication process, but even has tighter positional tolerances than the master composite. Since the compensation of positional errors typically only involves a slight translation or rotation of the master composite (within a fraction of a millimeter or up to 2°), it is particularly advantageous if the alignment step follows directly after exposure and fixation of the first hologram and takes place before moving the replication composite from the master composite. In particular, it is preferred that the replication composite remains in contact with a stationary surface of a master element, in particular with a base substrate, while the position adjustment takes place.This is because the adjustment can be performed with greater precision, eliminating the risk of errors caused by the flow of a composite track or inaccurate braking of the composite track. This adjustment process is explained below.

[0104] For exposing the first and second light-sensitive layers, it may also be preferable in some embodiments to use a master composite each, wherein the master composites have the same or different configurations. By exposing the first and second light-sensitive layers with two master composites, the exposure of the first hologram can take place in a first exposure station, while the exposure of the second hologram takes place in a second exposure station. For this purpose, the replication composite can advantageously be designed as a web that passes through the various stations. Thus, the fixation of the first hologram in the first exposure station can take place, for example, by activating a UV lamp or heat radiation unit.However, fixation can also be performed using a fixation module in a downstream workstation, which may include larger equipment to fix the first hologram more quickly. The space in the first exposure station does not need to be occupied by the fixation module, and the cycle time of a continuous replication process can be reduced.

[0105] Furthermore, this arrangement of master holograms at different workstations can increase the speed and throughput of the replication process. In particular, in series production, various process steps, such as exposure and fixation, can advantageously be performed simultaneously or in parallel with respect to the different color channels to increase the throughput of replicated polychromatic holograms.

[0106] The application of the second photosensitive layer to the fixed first hologram can take place in a separate workstation. This can enable the use of larger, dedicated equipment for applying the second photosensitive layer. The second photosensitive layer can, for example, comprise a liquid photopolymer that can be sprayed onto the fixed first hologram and preferably dried. In this way, other components can be safely shielded from the spraying process. Alternatively, the liquid photopolymer can also be applied using rollers or a chambered doctor blade. The second photosensitive layer can alternatively comprise a solid layer that is laminated to the first fixed hologram using one or more hot or cold laminating rollers. The second photosensitive layer can be self-supporting or comprise a carrier layer.Alternatively, a carrier layer can be laminated onto the already applied photosensitive layer. This may require space that is not available in the first exposure station and, in some embodiments, is best accomplished by moving the replication assembly through the workstation for applying the second photosensitive layer and / or additional intermediate layers. Furthermore, the replication assembly can be passed through additional intermediate processing stations between exposures.

[0107] In a further preferred embodiment of the invention, the first hologram is exposed using a first master composite or a master element. The second hologram is preferably exposed using a second master composite or a second master element. The first master composite or master element and the second master composite or master element are preferably constructed differently. For example, a first master hologram can only be present in the first master composite and a second master hologram can only be present in the second master composite. The layer structure of the master composites or master elements can thus be reduced. The risk of additional master holograms interfering with the exposure can be eliminated. This is particularly useful for transmission holograms when exposed with an RGB laser. The same applies to embodiments in which three master holograms are used.The three master holograms can each be provided in separate clusters or master elements.

[0108] Particularly when only a single master hologram is present in each master composite, alignment errors can be avoided by laminating multiple master holograms onto a single substrate. The master composite itself can thus be free of positioning errors. The master composite can be designed as a cylindrical substrate with a master hologram on its surface, so that exposure and fixation can take place continuously, especially when a replication composite is supplied in roll form. However, the exact positioning of the already exposed first hologram in the replication composite relative to the second master hologram in its own master composite can be challenging, particularly in the longitudinal direction. This embodiment can therefore be used for holograms that are generally homogeneous in the longitudinal direction.The master composite with a single master hologram can be configured as a plate and adjusted in position when a replica composite comes into contact with it. The positioning of the master composite can be adjusted to ensure that the polychromatic hologram has very tight positioning tolerances. Using only a single master hologram per master composite can also improve exposure quality by reducing unwanted reflections at the interfaces. This is because such a master composite comprises fewer material layers, which may have slightly different refractive indices. Optical losses at the interfaces between the layers can thus be eliminated or reduced.

[0109] The master substrate or a cover of the master substrate can provide a rigid surface to which an optical fluid can be applied to improve optical contact with the replication composite without the risk of leaving residue on the master holograms. This ensures a smooth optical transition of light rays between the master composite and the replication composite with minimal reflections and / or aberrations at interfaces. Such unwanted reflections cause optical losses, which reduce the efficiency of the replication process.

[0110] In a further preferred embodiment of the invention, exposure with the first and / or second master hologram takes place at a first and / or second exposure station. Preferably, the position of the respective master hologram relative to the replication composite is adjusted in the longitudinal and / or transverse direction at each exposure station. Preferably, the adjustment comprises a translation and / or rotation of the master hologram relative to the replication composite. This can be achieved by moving an entire master composite or a master element comprising the master hologram or a movable part thereof. Thus, the advantages of separate exposure stations can be combined with the advantages of improved tolerances in the replication composite.

[0111] In a further preferred embodiment of the invention, the replication composite comprising the first and / or second light-sensitive layer is brought into optical contact with the second master hologram. For this purpose, the replication composite is preferably laminated to a substrate, wherein the second master hologram is mounted so as to be movable with respect to the substrate. An optical fluid is preferably present between the master hologram and the substrate. This enables a preferably frictionless movement of the master hologram (or in particular of a master composite comprising the master hologram) with respect to the substrate. The optical fluid preferably has an identical or similar refractive index to that of the substrate and / or a surface of the master composite. A "similar refractive index" within the meaning of the invention is preferably a refractive index that deviates from the refractive index of an adjacent component by no more than 0.05, in particular no more than 0.03.This prevents unwanted reflections and losses at the interface between the substrate and the master composite. Preferably, the replication composite is laminated to the base substrate of a master element comprising the second master hologram.

[0112] In a further preferred embodiment of the invention, the second master hologram is provided in a master element. Optionally, the same master element also comprises the first master hologram. Preferably, the second master hologram is present in or on a master substrate, wherein the master substrate is movably mounted with respect to a base substrate of the master element. The replication composite is preferably temporarily laminated to the base substrate such that a carrier or protective layer of the replication composite is in contact with the base substrate. The base substrate preferably comprises a rigid transparent plate. For example, a section of a continuous composite web can be temporarily laminated to a surface of a base substrate by rolling. The lamination can be achieved using an optical adhesive film applied between the replication composite and the base substrate.This can stabilize the composite web for the duration of an exposure and / or fixation step.

[0113] In a further preferred embodiment of the invention, a translation and / or rotation of the master substrate is performed in order to position the second master hologram on the replication composite such that the second master hologram is precisely aligned with the already exposed first hologram. This translation and / or rotation can be performed according to pre-stored instructions. This is particularly efficient when the exposure steps are performed in the same workstation and the first and second master holograms are fixed to one another in a master composite. In this case, the alignment can be performed in the same way for each polychromatic hologram produced, so that by pre-storing the movement steps of the master composite, regular measurements of the alignment errors no longer need to be performed.

[0114] Preferably, the translation and / or rotation can be performed according to a detected position of the first hologram in the replication network. Detection of the position of the first hologram can be achieved, for example, using a sensor and / or an alignment mark. This allows the second master hologram to be precisely aligned with the first hologram.

[0115] The use of a base substrate enables the separation of functions between the master composite and the base substrate. The base substrate preferably has a flat surface. The base substrate can be configured, in particular, for optical contact with the replication composite. This advantageously allows the base substrate to be held stationary during the various phases of exposure, while the master composite can be aligned for optimal replication, as described. Advantageously, this way, no stresses or deformations are introduced into the replication composite by translation and / or rotation. Friction between the master composite and the replication composite, which could occur during alignment, is avoided. Such friction can impair alignment, preventing it from being performed to the required extent.Instead, there is a stable mechanical contact between the base substrate and the replication composite, while a relative movement for the alignment of the master holograms occurs within a two-part master element, in particular between a base substrate and a master composite.

[0116] The base substrate can preferably be mounted on a device that holds it securely. This serves to further improve the stability of the mechanical contact between the replication composite and the master element. By bringing the replication composite into contact with the base substrate and not with the master composite, the latter can be protected from friction, adhesive residue, and the like. The base substrate can thus be cleaned more easily, particularly by separating it from the master element and / or the holding device on which it is installed. The base substrate is also easier and more cost-effective to replace.

[0117] Furthermore, the base substrate allows for excellent optical contact between the replication composite and the master composite, while the master composite is spaced apart from the replication composite and remains freely movable. For this purpose, it may be preferred for the base substrate to comprise the same materials as the master composite, in particular the master substrate. The base substrate may additionally or alternatively comprise the same materials as an adjacent layer of the replication composite.

[0118] The base substrate is preferably configured such that the electromagnetic rays flow from the replication composite into the corresponding master hologram and back into the replication composite. The base substrate is preferably transparent to the wavelengths of the electromagnetic radiation with which the replication composite is to be irradiated at a corresponding workstation. The refractive index of the base substrate is preferably approximately equal to that of an adjacent layer of the replication composite, which can be a carrier layer or a replication substrate. The refractive index of the base substrate can preferably be between 1.4 and 1.6. This allows for very good optical contact between the replication composite and the base substrate, eliminating light loss due to total internal reflection at the interface between the replication composite and the base substrate.Such unwanted reflections can represent stray light that could impair the quality of the reproduced polychromatic hologram. This is advantageously prevented here.

[0119] In preferred embodiments of the invention, the optical contact between the replication composite and the base substrate is mediated by an intervening material. The material between the replication composite and the base substrate can be a solid, such as a film, in particular an adhesive film, or a deformable transparent element, e.g. made of silicone. The material can also be a semi-solid substance such as a gel. Alternatively, the material can comprise a fluid, such as an optical liquid. In preferred embodiments of the invention, the optical contact between the base substrate and the master composite is mediated by an intervening material. The material is preferably liquid so that it does not hinder the movement of the master composite relative to the base substrate.

[0120] During exposure, an optical fluid is preferably present between the master composite and the base substrate. Such an optical fluid preferably has a refractive index that corresponds to or is close to that of the base substrate, a master substrate, a master hologram, and / or the master holograms and improves the optical contact between them. An optical fluid advantageously achieves friction-free mobility of both components, while also enabling interference-free optical contact. The optical fluid can also absorb any vibrations that arise during exposure, particularly due to the movement of the master composite. The replication composite can thus be kept particularly stable during exposure.

[0121] To facilitate optical contact between the base substrate and the replication composite (in particular a replication substrate), some embodiments provide an optical adhesive film. Direct mechanical contact is preferably established between the optical adhesive film and the two adjacent substrates or between the base substrate and the replication composite. Should a gap be present between the surfaces of the optical adhesive film and adjacent substrates, it is preferably smaller than half a wavelength of the radiation used for exposure, so that no interference fields form at the interface between the surfaces. The optical adhesive film can thus improve the optical contact between the replication composite and the master element. It is particularly advantageous that the optical adhesive film need not be removed between exposure of the first and second master holograms into the replication composite.The optical adhesive film can also help stabilize the position of the replication composite relative to the master element, making the replication process particularly efficient.

[0122] In a further preferred embodiment of the invention, an optical fluid is introduced between the base substrate and the replication composite to establish optical contact. The optical fluid can advantageously be applied continuously, without a lamination step. On the one hand, this can be faster and more efficient than applying an optical adhesive film. At the same time, the risk of leaving adhesive residue on the base substrate can be avoided. Furthermore, the optical fluid can serve as a lubricant to protect the base substrate from surface damage.

[0123] The provision of a base substrate between the replication composite and the master composite, particularly by applying optical fluids and / or adhesive films at the interfaces, can also ensure particularly stable, vibration-free mechanical contact between the replication composite and the master composite. This significantly reduces the risk of unwanted displacement during the exposure process. Furthermore, the arrangement provides highly efficient optical contact, whereby the light rays used for exposure remain essentially unbroken on their path between a master hologram and a light-sensitive layer. The exposure process is thus highly efficient and produces sharp holographic images.

[0124] For the purposes of the invention, an "optical adhesive film" is preferably a transparent film with a refractive index close to the refractive index of the master substrate, the replication substrate, and / or the light-sensitive material. The optical adhesive film is preferably designed to improve optical contact between the base substrate and the replication composite, so that reflections at the interface between the base substrate and the replication substrate are reduced or eliminated.

[0125] Preferably, the materials used for the optical adhesive film have identical or similar optical properties to those used for the base substrate or the adjacent layer of the replication composite. These similar or identical properties preferably include transparency, haze, stress birefringence properties, and / or the refractive index. The use of identical or similar materials enables a very close adaptation of the refractive index of the optical adhesive film to the refractive indices of the adjacent base substrate and / or replication substrate, ensuring a transition between the adjacent refractive indices without refractive index jumps. Reflections at the interface between the master element, the optical adhesive film, and / or the replication composite are thereby largely eliminated or significantly minimized.

[0126] An "optical fluid" within the meaning of the invention is preferably a transparent fluid with similar or identical optical properties to the base substrate, master substrate, master composite, replication substrate, and / or replication composite. The similar or identical properties preferably include transparency, haze, stress birefringence properties, and / or the refractive index. The use of an optical fluid can prevent unwanted reflections at the interfaces between components.

[0127] In a further preferred embodiment of the invention, the base substrate comprises an optical glass and / or an optical plastic. The optical glass or optical plastic is preferably selected from the following group: polymethyl methacrylate (PMMA), polycarbonate (PC), cycloolefin polymers (COP), and cycloolefin copolymers (COC), and / or an optical glass is preferably selected from the group: borosilicate glass, quartz glass, B270, N-BK7, N-SF2, P-SF68, P-SK57Q1, P-SK58A, and P-BK7. The base substrate preferably has a refractive index between 1.4 and 1.6.

[0128] In a further preferred embodiment of the invention, the master composite can be used without a base substrate. In this case, it is preferred that the replication composite be placed at a predetermined distance from the master composite during exposure. The predetermined distance is preferably large enough to prevent unwanted mechanical contact between the master composite and the replication composite. However, the predetermined distance is preferably also small enough to be bridged by an optical fluid that is held stable by intermolecular forces. Preferably, an optical fluid is introduced between the master composite and the replication composite.

[0129] In a further preferred embodiment of the invention, the first and / or second master hologram are provided in a master assembly comprising a master substrate. The master substrate is preferably positioned on the replication substrate of the replication assembly. An optical fluid is preferably applied between the master substrate and the replication substrate. In such an embodiment, the replication substrate can be rigid and assume the function of the base substrate. The replication substrate can support the optical contact with the master hologram and simultaneously provide a support surface for the lamination of further layers. With a rigid replication substrate, an optical adhesive film is preferably used only to bring the replication substrate into contact with another stationary part, in particular with the base substrate of a master element.Alternatively, the replication substrate can be in the form of a film. If a film-like replication substrate is brought into contact with a movable master element, optical contact between the movable master element and the replication substrate is preferably determined using an optical fluid.

[0130] In preferred embodiments, the base substrate, the master composite, in particular the master substrate, and / or a replication substrate can be provided with an anti-reflection coating. Such a coating can contribute to further reducing efficiency losses due to reflections.

[0131] In some embodiments, a rigid replication substrate can be used instead of the base substrate. In this way, the rigid replication substrate can be bonded to the remaining layers of the replication composite and further processed with them. In embodiments where the replication substrate is used instead of the base substrate, an optical fluid can be disposed between the replication substrate and the master composite. This would offer analogous advantages to the application of an optical fluid between the base substrate and the master composite. In such embodiments, the substrate is preferably individual for each polychromatic hologram. In-situ lamination of an optical adhesive film to the base substrate can be omitted, allowing for faster exposure. The optical adhesive film also does not need to be removed after exposure.The need to clean the base substrate can also be eliminated; instead, a polychromatic hologram can be built directly on the replication substrate and exhibit very good quality.

[0132] In some applications, the rigid replication substrate can form part of the final product, e.g., as a carrier layer to incorporate the polychromatic hologram into a final product. This is particularly advantageous when multiple polychromatic holograms are to be stacked on top of each other in a precise relative position. Using rigid replication substrates for the different polychromatic holograms offers an alternative to roll-based stacking or lamination processes, which can result in deformation of the replication composites. The replication substrates can include positioning marks. These can, for example, be used to precisely position two polychromatic holograms on top of each other, so that the two polychromatic holograms are encapsulated between the two replication substrates, with the respective positioning marks aligned.In embodiments of the invention, the exposed and preferably fixed polychromatic hologram can be delaminated from the rigid replication substrate to obtain a flexible polychromatic hologram. The rigid replication substrate can then be reused.

[0133] The replication substrate can provide the replication composite with sufficient rigidity to ensure its stability during multi-step exposure. Furthermore, the strength and rigidity of the replication substrate can enable the lamination of additional layers and / or the removal of layers from the replication composite between exposure steps without undesirable deformation of the replication composite. This allows the application of additional light-sensitive layers at separate workstations without the replication composite being in contact with the master element.

[0134] In a further preferred embodiment of the invention, the replication substrate is in film form. Such a replication substrate can also carry the polychromatic hologram. Furthermore, the replication substrate can comprise positioning marks that serve to stack multiple polychromatic holograms on top of one another, so that the positioning marks can later be cut away or the replication substrate can be removed from the final product. In such embodiments, the replication substrate can preferably be supplied in roll form so that it can be laminated to the rigid surface of a base substrate and easily transported to further workstations in a continuous process. In such an embodiment, the produced polychromatic hologram can advantageously be flexible, which facilitates its integration into a three-dimensional component such as a windshield.

[0135] In preferred embodiments of the invention, a translation and / or rotation of the master hologram is controlled by a control unit. Thus, the translation and / or rotation can be performed particularly precisely and repeatably.

[0136] The term "control unit" preferably refers to any computer unit comprising a processor, a processor chip, a microprocessor, or a microcontroller that enables automatic control of one or more actuators, e.g., a carriage, a motor, a brake, an electromagnet, etc. The components of the control unit can be conventional or individually configured for the respective implementation. Preferably, the control unit comprises a processor, a memory, and computer code (software / firmware) for controlling the components of the device.

[0137] The control unit may also comprise a programmable circuit board, a microcontroller, or other device for receiving and processing data signals from the components of the device, for example, from sensors relating to the speed of a composite web and / or the position of a master hologram, in particular the position of an alignment mark of the master hologram, as well as other relevant sensory information. The control unit preferably further comprises a computer-usable or computer-readable medium, such as a hard disk, random access memory (RAM), read-only memory (ROM), flash memory, etc., on which computer software or code is installed. The computer code or software for controlling the components of the device may be written in any programming language or model-based development environment, e.g.in C / C++, C#, Objective-C, Java, Basic / VisualBasic, MATLAB, Python, Simulink, StateFlow, Lab View or Assembler, but not only.

[0138] The term "control unit is configured to" perform a specific operation, such as translating and / or rotating the master assembly, may include custom or standard software installed on the control unit that initiates and controls these operational steps.

[0139] In a further preferred embodiment of the invention, reference values ​​for a degree and / or a direction of a required translation and / or rotation of the first and second master holograms are stored in a memory. Preferably, the control unit is configured to control a translation and / or rotation of the master array (comprising the first and second master holograms) according to the reference values. In preferred embodiments, the reference values ​​are automatically provided to the control unit repeatedly for a series of replication arrays (or a series of sections of a continuously supplied replication array). By preloading reference values ​​into a memory, the alignment of the master holograms can be performed for repetitions of the same sequence of exposure steps without recalculating the required alignment.Time-consuming steps for converging to an alignment position of the master holograms can be skipped. This allows for very fast and automated processing of unexposed replication arrays or unexposed light-sensitive layers.

[0140] In some preferred embodiments of the invention, instructions for the alignment of the first and second master holograms are determined experimentally. For this purpose, the first and second holograms can be provided with alignment marks during their manufacture. The alignment marks of the holograms can be compared with an external alignment mark outside the master composite, which represents the target position of the holograms. For example, the external alignment mark can be present on the replication composite or on a base substrate. Alternatively, the external alignment mark can be present only in software, for example, as a predetermined image coordinate.

[0141] It may be preferred that the required alignment of a hologram is determined by translating and / or rotating the master composite until an alignment mark of each of the first and second holograms spatially coincides with the external alignment mark representing the desired position of the respective hologram. This can be performed by incremental translation and / or rotation of the respective hologram and an assessment of the correspondence of the respective alignment mark with the desired alignment mark. The evaluation can be performed using software, in particular using image analysis software. It may also be preferred that a degree and / or direction of a translation and / or rotation direction of the hologram, at which the best alignment or the best image quality was assessed, is stored in the memory.The selection of the translation and / or rotation positions to be tested can be performed repeatedly to converge on a position with the best alignment. Preferably, a converging function can be used to select the translation and / or rotation positions, i.e., preferably a mathematical or algorithmic process based on refining an estimated value until it is sufficiently accurate within defined limits or converges to an optimum. The converging function for selecting optimal translation and / or rotation positions can be based, for example, on an iterative or recursive algorithm.

[0142] As an alternative to using alignment marks, the holographic image or the optical function of each master hologram can be compared with a correctly aligned target function. This can be done by reconstructing the hologram, particularly the relevant wavelength channel, and evaluating the correspondence of all or part of the reconstructed hologram with the target function. This can also be done using software, particularly image analysis software.

[0143] In a further preferred embodiment of the invention, to determine the degree and direction of a required translation and / or rotation of the first and / or second master hologram, the master composite is irradiated with collimated reconstruction light to generate a convergent point (e.g., a focus). This is particularly suitable for master holograms that have the optical function of a concave mirror or a light-focusing lens.

[0144] Preferably, a degree and / or direction of a required translation and / or rotation of the first and / or second master hologram is selected such that a convergent point for reconstruction light of the first wavelength range coincides with a convergent point for reconstruction light of the second wavelength range. An external target point can be used as a reference for the position of the convergent point. Alternatively, the point at which either the first or the second master hologram actually converges the light can also be used.

[0145] In this way, the different wavelength channels can be exposed in such a way that all channels of the polychromatic hologram also focus a planar wavefront to a single point. This allows the polychromatic hologram to fulfill the optical function of a conventional optical element in a much more compact form without chromatic aberration.

[0146] In further preferred embodiments of the invention, additional or alternative alignment methods can be used to determine the required alignment of the individual master holograms in the master assembly. For example, each master hologram can be provided with a positioning mark. The master assembly can thus be gradually shifted until the position of the positioning mark coincides with a desired position. The positioning mark can take any form, such as an imprint, a notch, or a holographic element.

[0147] Preferably, a required translation and / or rotation to achieve the best alignment for a master hologram is captured as an instruction in memory. Preferably, the control unit is configured to signal an actuator to translate and / or rotate the master hologram according to the pre-captured instructions.

[0148] To perform the translation or rotation, it may be advantageous to provide an alignment module. This may comprise a gantry structure in which the master assembly is positioned. It may also be preferred for the master assembly to be positioned in or on a carriage that can be translated about two orthogonal axes, e.g., by means of pins, rails, or the like. It may be preferred for the carriage to be located on a rotatable support connected to a motor, e.g., a piezoelectric motor. Of course, further pins, gears, or the like may be provided to finely adjust and / or limit the movement.

[0149] In a further preferred embodiment of the invention, the first and second master holograms are arranged in or on a master substrate to form the first master composite, wherein the master substrate is preferably translated and / or rotated by an alignment module to perform an alignment.

[0150] The master substrate is preferably configured to support the layer structure of the first and second master holograms, and optionally third or further master holograms. The first and second master holograms are preferably laminated to a surface of the master substrate to create the layer structure. The master substrate is preferably rigid and transparent to the first and second wavelength ranges. The dimensions of the master substrate are preferably larger than those of the master hologram in all directions. The master substrate preferably has a thickness that is at least 5 times, preferably at least 10 times, and even more preferably at least 10 times the thickness of the first or second master hologram. The master substrate can preferably have the shape of a cuboid block, a plate, a cylinder, or a prism.At least one surface of the master substrate is preferably parallel to the master holograms and traverses the longitudinal and transverse directions.

[0151] Preferably, the master substrate can be formed from a material that is an optical plastic, preferably selected from the group: polymethyl methacrylate (PMMA), polycarbonate (PC), cycloolefin polymers (COP), and cycloolefin copolymers (COC), and / or an optical glass, preferably selected from the group: borosilicate glass, quartz glass, B270, N-BK7, N-SF2, P-SF68, P-SK57Q1, P-SK58A, and P-BK7. The master substrate preferably has a refractive index between 1.4 and 1.6.

[0152] By attaching the first and second master holograms to or integrating them into the master substrate, the master composite can be made extremely robust and protected against damage. Due to its larger dimensions and higher rigidity, it can also be translated and rotated more reproducibly without the risk of stretching, shrinking, or otherwise deforming. Furthermore, precise translation and / or rotation is facilitated.

[0153] It may also be preferred that the light-sensitive layers of the first replication composite be applied, exposed, and fixed in a mirror-symmetrical sequence with respect to the layer structure of the master hologram. The mirror symmetry here particularly applies to the light-sensitive layers of the replication composite. In this way, the optical function of the generated polychromatic hologram can correspond exactly to the optical function of the multilayer master hologram. When reversed, such a polychromatic hologram has the same layer structure as the master hologram. The arrangement of the layers can be configured, in particular, to minimize filter effects between the layers and to improve the efficiency of the optical function of the polychromatic hologram.

[0154] In a further preferred embodiment of the invention, one of the first, second, or third wavelength ranges corresponds to red light, another wavelength range of the first, second, or third wavelength ranges corresponds to green light, and yet another wavelength range of the first, second, or third wavelength ranges corresponds to blue light. For example, the first wavelength range corresponds to red light, the second wavelength range to green light, and the third wavelength range to blue light.

[0155] In a further preferred embodiment of the invention, one of the first, second, or third wavelength ranges corresponds to red light, wherein the wavelength range is preferably between 590-750 nm, particularly preferably between 620-700 nm. Preferably, one of the first, second, or third wavelength ranges corresponds to green light, wherein the wavelength range is preferably between 490-590 nm, particularly preferably between 500-560 nm. Preferably, one of the first, second, or third wavelength ranges corresponds to blue light, wherein the wavelength range is preferably between 380-490 nm, particularly preferably between 420-475 nm.

[0156] In this way, a polychromatic RGB (red-green-blue) hologram can be created. Such a hologram can create the illusion of redirecting light from essentially the entire visible spectrum, thus producing full-color holographic images with a high degree of sharpness. Such images can achieve very high visual quality due to the precise alignment of the channels. The polychromatic RGB hologram can also redirect white light in a compact manner, which is particularly useful for HOEs integrated into car, aircraft, or other vehicle windows.

[0157] In a further preferred embodiment of the invention, the first, second, and third master holograms are reflection holograms. Reflection holograms can be replicated particularly efficiently using the method according to the invention to produce sharp images. A particularly preferred embodiment of a reflective polychromatic hologram is a so-called "Z-hologram," which can convert a spherical wavefront into a planar wavefront with a predetermined radiation angle. This is explained further below with reference to Fig. 8.

[0158] In a further preferred embodiment of the invention, the photosensitive layers comprise a photopolymer. The photopolymer is preferably sensitive to light of at least the first and second wavelength ranges. The use of photopolymers in the photosensitive layers can be advantageous because they are available in a variety of formulations and can be combined with various additives and pretreatments to adjust their viscosity, refractive index, and / or wavelength selectivity. For example, photopolymers can be provided in liquid form and applied to a replication composite to form a photosensitive layer. The thickness of each photopolymer layer can be adjusted by adjusting the application mechanism.Such a light-sensitive layer does not require adhesives for stable adhesion to the replication composite and can then be fixed directly after exposure. This is particularly advantageous for forming a thin multilayer structure in the replication composite without the use of adhesive or carrier layers between the light-sensitive layers. Optionally, however, photopolymers can be provided in liquid form between two transparent carrier films, which can be bonded to an existing replication composite, for example, using a suitable transparent adhesive.

[0159] Photopolymers can also be provided as resins or solids, for example, through a pretreatment that partially fixes the photopolymer, preferably prior to exposure. The resin or solid photopolymer can be applied to a single support layer, with the uncovered surface adhering to the replication composite without the use of an adhesive. Optionally, the support layer can be removed after application of the resin or solid photopolymer to the replication composite, particularly after exposure and fixation of the photopolymer. The solid photopolymer layer can also be self-supporting. Photopolymers thus offer great flexibility in designing the structure of the replication composite.In particular, they can allow the replication composite to expose holograms in different layers while maintaining a low overall thickness, since adhesive layers and carrier layers can be omitted in some cases.

[0160] In a further preferred embodiment of the invention, the application of a light-sensitive layer takes place by gluing. The application of a light-sensitive layer by gluing can be particularly preferred when the light-sensitive layer is present between carrier layers. In a preferred embodiment, the gluing takes place by applying an optical adhesive film to the replication composite and / or to a carrier layer of the light-sensitive layer. The optical adhesive film can in particular be configured for permanent adhesion and have an identical or similar refractive index to an adjacent carrier layer or a light-sensitive material. The optical adhesive film can be applied to the replication composite by removing a protective layer and by laminating. In a further preferred embodiment, an adhesive is applied to the replication composite by spraying, painting or printing.

[0161] In a further preferred embodiment of the invention, a light-sensitive layer is applied by lamination. The lamination is preferably carried out using at least one lamination roller at 20–300°C, preferably 40–200°C, in particular 60–80°C. The lamination can be designed to at least partially bond a carrier film on the replication composite to a carrier film of the light-sensitive layer. The lamination temperature is preferably selected depending on the materials of the two carrier films so that one or both are brought to their melting point for a short period of time. The preferred temperature preferably also depends on the photopolymer formulation and should not impair the light sensitivity of the photopolymer.

[0162] Lamination is preferably performed at a compressive force between 10–20,000 N. The required compressive force preferably depends on the width of the photosensitive layer, the target layer thickness, and / or the lamination speed. Applying a preferred compressive force can, in particular, increase the adhesion of a photosensitive layer, especially a solid photosensitive layer, to the replication composite. Any air gaps between the photosensitive layer and the replication composite can be eliminated, so that no unwanted reflections occur at the interface. This allows excellent optical contact between the replication composite and the newly added photosensitive layer to be achieved. In some embodiments, lamination is combined with the application of an adhesive layer to achieve a seamless bond between the layers of the replication composite.Preferably, the lamination of a photosensitive layer onto a replication composite takes place directly onto a substrate in an exposure station. The substrate is preferably fixed in position during exposure and lamination. Preferably, the substrate is a replication substrate or base substrate. This means that lamination can take place in place where exposure also takes place, without having to move the replication composite to a separate lamination station. Since movement of the replication composite can lead to positioning errors, particularly in the longitudinal direction, this can be avoided by performing the lamination step in situ. The use of a solid substrate, particularly with a flat surface, enables the application of high pressure when applying the new photosensitive layer.This allows the new light-sensitive layer to have a predetermined thickness and adhere well to the underlying layers.

[0163] In a further preferred embodiment of the invention, the application of the light-sensitive layers comprises a coating of a photopolymer in liquid form and optionally drying. The coating of a photopolymer can be applied directly to the replication composite or to a carrier layer, which is subsequently applied to the replication composite. Coating a liquid photopolymer to form the light-sensitive layer can reduce the thickness of the multilayer polychromatic hologram, since liquid photopolymers can adhere particularly well to a replication composite without the use of intermediate layers. This allows additional carrier or adhesive layers to be omitted, simplifying the process.

[0164] Preferably, the coating of a photopolymer is carried out using a coating module. In a further preferred embodiment of the invention, the coating module is configured to coat the liquid photopolymer onto a first carrier film using a roll-to-roll process. The coating module can comprise one or more coating elements, whereby the suitable coating element can be selected depending on the layer thickness and rheological properties of the photopolymer. The following can be preferred as coating elements, for example: an anilox roller, a wire doctor blade, a profile doctor blade, a slot die, a doctor blade, a chamber doctor blade, a comma doctor blade, and / or means for a doctor blade process.

[0165] In a further preferred embodiment of the invention, the coating module is configured to coat the liquid photopolymer onto a surface of the replication composite. The liquid photopolymer is preferably applied by printing, rolling, brushing, or spraying. Such processes make it possible to apply the liquid photopolymer to only part of the surface of the replication composite. This allows further patterns to be formed in the polychromatic hologram. The thickness of a photopolymer layer is preferably 1–200 μm. For photopolymer layers with thicknesses between 1–15 μm, it is preferable to use an anilox roller in a gravure printing process. For photopolymer layers with thicknesses between 7–40 μm, wire or profile doctor blades are preferred. If the layer thickness is between 40 and 100 μm, a slot die, a doctor blade, or a comma doctor is preferably used.

[0166] In a further preferred embodiment of the invention, the method comprises the use of two coating modules, wherein a first coating module is configured to coat a first carrier film with a liquid photopolymer and a second coating module is configured to coat a second carrier film with a liquid photopolymer. The method preferably comprises corresponding coating steps. By separately coating two films and joining them together, thinner coating layers can be combined to form a thicker photopolymer layer. Preferably, a combining step is carried out by laminating the two coated carrier films in order to enclose the photopolymer layer between them. It is advantageous that thinner layers are degassed more quickly. The solvents in the coatings can evaporate more quickly before the lamination process.

[0167] Furthermore, the coating of additional carrier films can enable the production of photopolymer stacks. For example, a stack of two or more liquid photopolymer layers, each separated by a carrier film, can in particular comprise two different photopolymer compositions, where, for example, each composition is sensitive to light of a specific wavelength range. For example, a second, third, or further hologram can be exposed in different photopolymer layers without applying a new light-sensitive layer to the replication composite between these exposure steps. This can be particularly efficient if the second, third, or further holograms can be exposed at the same workstation and do not need to be combined with each other, e.g., as a multiplex hologram in a single layer.This can also be efficient in cases where the photopolymer layers of the photopolymer stack are wavelength-selective and / or the corresponding master holograms do not require alignment. These photopolymer layers can be exposed in one workstation. Fixation can then be performed for all photopolymer layers of the photopolymer stack.

[0168] In a further preferred embodiment of the invention, the replication substrate, the photosensitive layers, and / or the replication composite are present in the form of a web of any desired length. The replication substrate can take the form of a transparent film, wherein the film can preferably be supplied in roll form. The photosensitive layers can each be supplied with at least one carrier film, wherein the carrier film is optionally removed after application of the photosensitive layer to the replication composite. In this way, the photosensitive layer is transferred to the replication composite without excessively increasing the thickness of the replication composite by means of intermediate layers. Preferably, the photosensitive layer is also supplied in roll form. The replication composite can also be supplied in roll form and further built up during the process.Preferably, the replication cluster can be rolled back after the replication cluster.

[0169] Providing the replication substrate, the photosensitive layers, and / or the replication composite as a single web of any length allows the use of rollers to transport the respective web through various workstations. This arrangement is particularly suitable for a continuous process, allowing short cycle times and high throughputs to be achieved. Furthermore, web movement can be limited so that rotational and / or lateral offset is preferably impossible or severely limited. For example, the dimensions of the transport rollers can be adapted so closely to the width of the web that unwanted movement of the web in a transverse direction is prevented.

[0170] In a further preferred embodiment of the invention, the replication substrate, the light-sensitive layers, and / or the replication composite are transported on a flow path by means of transport rollers. The replication process preferably takes place continuously. The use of a flow path can be particularly advantageous when the replication substrate is configured as a solid three-dimensional body. Since such a replication substrate cannot be rolled up, it is advantageous to process the replication substrate in a continuous process using transport rollers. The transport rollers can also prevent unwanted movement of the replication substrate, the light-sensitive layers, or the replication composite in a transverse direction, in particular by adapting the width of the transport rollers to the width of the replication substrate.This can also limit unwanted rotational movement.

[0171] In a further preferred embodiment of the invention, steps a. to k. are repeated analogously to replicate a polychromatic hologram into a second replication composite using a fourth, fifth, and sixth master hologram. The first and second replication composites can be combined to fulfill a more complex optical function.

[0172] For example, the two replication arrays may comprise reflection holograms, wherein an incident beam is reflected by a first replication array, such that the beam impinges on and is deflected by the second replication array. Preferably, one of the first and second replication arrays is exposed using a planar wavefront. Preferably, the other of the first and second replication arrays is exposed using a spherical wavefront. In this way, one of the two polychromatic holograms can be configured to convert a spherical wavefront into a planar wavefront, and the other of the two polychromatic holograms can be configured to reflect a planar waveform at a predetermined angle.

[0173] The polychromatic holograms can perform the function of a convex mirror or a planar mirror (together, the function of a convex lens) in a very compact manner without unwanted chromatic aberration. Since the polychromatic holograms can be manufactured from light-sensitive materials with thicknesses in the micrometer range, they can perform their respective optical functions with high efficiency across multiple wavelength ranges while requiring very little space. They can therefore be discreetly integrated into AR glasses, car windshields, aircraft windows, pilot training devices, and the like.

[0174] In a further preferred embodiment of the invention, the first and second replication composites or the first and second polychromatic holograms are connected to one another, wherein the first and second polychromatic holograms are preferably arranged at a distance of less than 1 mm, preferably less than 0.5 mm, particularly preferably less than 0.1 mm. The first and second polychromatic holograms preferably have a layered structure, wherein a first layer corresponds to a first wavelength range and a second layer corresponds to a second wavelength range. The polychromatic holograms are preferably arranged such that their layers are mirror-symmetrical to one another - that is, the order of the layers corresponding to each wavelength range is preferably the same from the center line outwards.

[0175] In this way, a light-redirecting HOE can be manufactured with very tight tolerances, resulting in a very high efficiency. Since only the two polychromatic holograms could be applied and bonded together in a conventional manner, e.g., by lamination, only one alignment of the two generated polychromatic holograms is required. This represents a significant improvement over the state of the art, in which six layers must be aligned and laminated to create such a multilayer RGB hologram. The precision of the HOE can be drastically improved. The resulting polychromatic HOE can combine the functions of the convex mirror and the planar mirror to perform complex redirection of electromagnetic beams in a very compact manner.

[0176] In a further aspect, the invention relates to a replication composite comprising at least a first and a second replicated hologram, wherein the replication composite can be produced by the method according to the invention or preferred embodiments thereof.

[0177] The first and second replicated holograms can preferably be present in one or more layers of fixed photosensitive material to provide a polychromatic hologram. The first hologram is preferably exposed to a wavelength from a first wavelength range, while the second hologram is preferably exposed to a different wavelength from a second wavelength range, so that the resulting replication composite can diffract radiation of both wavelengths. Furthermore, the replication composite can comprise further layers such as carrier films, protective layers, and / or the replication substrate.

[0178] Such a replication array advantageously comprises diffraction structures configured to diffract radiation at two or more different wavelengths. The diffraction structures corresponding to the different wavelengths are advantageously precisely aligned with each other, ensuring the replication array is of high quality and fulfills its optical function very efficiently. Unwanted filtering of light due to incorrect alignment of the different wavelength channels relative to each other is avoided.

[0179] The average person skilled in the art recognizes that technical features, definitions and advantages of preferred embodiments of the method according to the invention also apply to the replication network according to the invention, and vice versa.

[0180] Detailed description

[0181] In the following, the invention will be explained in more detail using examples and illustrations, without being limited to these.

[0182] Short description of the figures

[0183] Fig. 1 is a schematic representation of the structure of a master composite comprising three master holograms in different layers.

[0184] Fig. 2 is a schematic representation of the step-by-step construction of a polychromatic hologram in a workstation using a master array.

[0185] Fig. 3A is a schematic representation of the alignment of the first master hologram so that its focus point coincides with a reference point.

[0186] Fig. 3B is a schematic representation of the exposure of a first master hologram into a first photosensitive layer of a replication composite.

[0187] Fig. 4A is a schematic representation of the alignment of the second master hologram to match the focal point of the first master hologram and / or the first replicated hologram.

[0188] Fig. 4B is a schematic representation of the exposure of a second master hologram into a second photosensitive layer of the replication composite. Fig. 5A is a schematic representation of the alignment of the third master hologram to match the focal point of the first and second master holograms and / or the first or second replicated hologram.

[0189] Fig. 5B is a schematic representation of the exposure of a third master hologram into a third photosensitive layer of the replication composite.

[0190] Fig. 6 is a schematic representation of the step-by-step construction of a polychromatic hologram using a single master composite.

[0191] Fig. 7 is a schematic representation of a polychromatic holographic-optical element (in particular a “z-hologram”) comprising six holograms in a layer structure, which can be produced by the method according to the invention.

[0192] Fig. 8 shows the holographic optical element of Fig. 7 and its light-deflecting function.

[0193] Detailed description of the illustrations

[0194] Fig. 1 schematically shows the structure of a master composite 2 with three master holograms, which correspond to the three wavelength channels, in particular RGB channels. The figure shows the master composite 2 in plan view at various stages of its production. The master composite 2 comprises a master substrate 10, which can be a glass plate, for example. A first master hologram 4 is laminated to a surface of the master substrate 10. The first hologram 4 is designed for a first wavelength range Ai, for example, a blue region of the visible spectrum. The master substrate 10 has a length and width that are greater than the length and width of the first master hologram 4. This can be seen in the first image of Figure 1.

[0195] A second master hologram 6 is laminated onto the composite comprising the master substrate 10 and the first master hologram 4. The second master hologram 6 is designed for a second wavelength range, in particular a green range of the visible spectrum. As illustrated in the second image of Fig. 1, a position shift between the second master hologram 6 and the first master hologram 4 can occur during lamination. This means that a longitudinal, transverse and / or rotational position of the second master hologram 6 may not exactly match the longitudinal, transverse and / or rotational position of the first master hologram 4. Furthermore, the positions of the first and second master holograms 4, 6 may not exactly match their target positions on the master substrate 10.

[0196] A third master hologram 8 is subsequently laminated onto the second master hologram 6 and forms part of the layer structure of the resulting master composite 2. The third master hologram 8 corresponds to a third wavelength range As, for example, a red region of the visible spectrum. Here, too, an offset occurs during lamination, so that the position of the third master hologram 8 does not exactly coincide with the position of the first master hologram 4 or the second master hologram 6. Optionally, the master composite 2 can be provided with a transparent cover (not shown) to protect the master holograms. In the exemplary embodiment, the three master holograms 4, 6, and 8 are reflection holograms and have an optical function for concentrating incident radiation.

[0197] Due to the offset between the channels of the master composite 2, the quality of a holographic image generated by its reconstruction or its optical function may be limited. Color channels of the master composite 2 do not exactly match each other, so that areas of the master composite 2 may appear in the wrong color tone. Using the method according to the invention, a master composite 2 with high tolerances can nevertheless be used to produce a polychromatic hologram 20 with extremely tight tolerances.

[0198] The master assembly 2 is preferably arranged on a base substrate 42 and provided with an alignment module to form a master element 12. The alignment module can change the translational or rotational position of the master assembly 2 with respect to the base substrate 42. The base substrate 42 preferably comprises a transparent, rigid plate.

[0199] Fig. 2 shows a method for producing a polychromatic hologram according to a further embodiment. The step-by-step construction preferably takes place in a single workstation using the same master composite. A replication substrate 43 is provided (top left in Fig. 2). A first light-sensitive layer 14 is applied to the replication substrate 43 by lamination to form a replication composite 44. The replication composite 44 is guided to an exposure station. A light source 48 generates coherent beams of a first wavelength range. The beams are reflected by a first master hologram 4 in the master composite 2. The coherent beams of the first wavelength range are used to expose the first master hologram 4 to generate a first hologram in the first light-sensitive layer 14.After exposure of the first light-sensitive layer 14, the replication composite 44 is cured (top right in Fig. 2). A UV lamp 50 as well as heat and / or white light can be used to fix the first hologram. The UV lamp 50 and other fixation devices can only be activated and / or scanned over the replication composite during this step.

[0200] Without moving the replication composite, a second light-sensitive layer 16 is applied to the replication composite 44. The second light-sensitive layer 16 can be applied directly to the first light-sensitive layer 14 or to an intermediate layer. The second light-sensitive layer 16 is sensitive to a second wavelength range. The second master hologram 6 is exposed to radiation of the second wavelength range from a radiation source 48 in the same exposure station with the same master composite 2. The master composite 2 comprises the second master hologram 6. Before exposure, the second master hologram 6 is preferably aligned in order to adjust its positioning over the first exposed hologram. For this purpose, the master composite 2 is preferably translated and / or rotated. The magnitude and direction of the translation and / or rotation are preferably determined by detecting the actual position of the first hologram.For example, this is achieved by reconstructing the first hologram and / or detecting a position marker. The second master hologram 6 can thus be precisely positioned relative to the first hologram to produce a polychromatic hologram with very tight tolerances. The light-redirecting function of the second master hologram 6 is replicated in the second light-sensitive layer 16. The exposed second light-sensitive layer 16 is then fixed in the same workstation.

[0201] A third light-sensitive layer 18 is then applied to the replication composite 44 in the same workstation without moving the replication composite 44. The third light-sensitive layer 18 is designed for a third wavelength range. Radiation of the third wavelength range is used to replicate the third master hologram 8 into the third light-sensitive layer 18. Before exposing the third master hologram 8, it is preferably aligned to adjust its position relative to the exposed first hologram and / or the exposed second hologram. The light-redirecting function of the third master hologram 8 is then replicated in precise alignment in the third light-sensitive layer 18. The third hologram is then fixed.The result is a polychromatic hologram 20 with three holograms in different layers, whereby the holograms have an improved positional accuracy compared to a laminated hologram structure and also compared to the master composite 2.

[0202] In alternative embodiments of the invention, the above-mentioned steps can be performed at different workstations. For example, a replication substrate can be fed to three different exposure stations to replicate the first, second, and third master holograms. Each exposure station is preferably equipped with a different master composite 2. A first master composite 2 preferably carries the first master hologram 4, a second master composite preferably carries the second master hologram 6, and a third master composite preferably carries the third master hologram 8. Between successive exposure stations, a station for applying a new light-sensitive layer (for example, by lamination or coating) and a fixing station are preferably interposed.

[0203] Figures 3A and 3B schematically show a replication of the first master hologram 4 of the master composite 2 from Fig. 1 into a light-sensitive layer 14 of a replication composite 44. The master composite 2 is part of a master element 12, which further comprises a base substrate 42, which is designed to be movable relative to the master composite 2. In a first exposure step, the replication composite 44 comprises a first light-sensitive layer 14 and protective layers located underneath and above it. The layer structure of the replication composite 44 is built up step by step by applying further light-sensitive layers. The advantage here is that the light-sensitive layers do not have to be wavelength-selective. The master holograms 4, 6, and 8 are preferably exposed in a mirrored order into the replication composite 44.Since in this case the first master hologram 4, which corresponds to blue light, is closest to the first light-sensitive layer 14 of the replication composite 44, the first exposure step is carried out with blue light, in particular with a blue laser.

[0204] A top side of the base substrate 42 and a bottom side of the master substrate 10 are arranged at a predetermined distance from each other and each provided with an anti-reflection layer so that no unwanted reflections occur on these sides. An optical fluid 30 is introduced between the top side of the base substrate 42 and the bottom side of the master substrate 10 so that a light beam can cross the distance between the base substrate 42 and the master substrate 10 essentially without diffraction. To further prevent unwanted reflections at the interface between the replication composite 44 and the base substrate 42, an optical adhesive film is inserted between these components for the duration of the steps shown in Figs. 3A-5B. This optical adhesive film is not shown in the figures.

[0205] Before exposure, the first master hologram 4 is first arranged such that it is in a desired position with respect to the replication composite 44. This is done by translating and / or rotating the master composite 2 comprising the first master hologram 4, as schematically shown in Fig. 3A. The base substrate 42 remains stationary. The position of the base substrate 42 is shown in dashed lines. As explained further below for Fig. 4A and Fig. 5A, this position remains unchanged during the three exposure steps. The translation and rotation of the master composite 2 are preferably carried out by an alignment module according to previously stored instructions. The desired position can be a position at which the blue light used to reconstruct the first master hologram 4 converges to a convergence point 40 that corresponds to a predetermined coordinate.The position of the convergence point 40 can be stored in advance and compared with the data of a light detector monitoring the reconstruction of the first master hologram 4 to determine the alignment instructions.

[0206] The position of the master hologram 4 can also be adjusted relative to the position of an underlying base substrate 42. For example, the master hologram 4 can be centered directly above the base substrate 42 with a predetermined margin, as schematically illustrated in Fig. 3A.

[0207] To replicate the first master hologram 4, a planar wavefront comprising reference rays 26 of blue light is irradiated onto the first master hologram 4. This process is schematically illustrated in Fig. 3B. The reference rays 26 pass through the first photosensitive layer and are reflected by the first master hologram 4. A reflected object beam 28 interferes with the reference beam 26 in the first photosensitive layer 14, forming an interference pattern therein. A first hologram 140 (shown in the following figures) is generated in the photosensitive layer of the replication composite 44. The first hologram 140 can be reconstructed with blue light (or light comprising a blue region of the spectrum) and fulfills the optical function of converting a spherical wavefront into a planar wavefront. The first hologram 140 is fixed (not shown) before further exposure steps are performed.This can be done by activating a fixation module in the same workstation.

[0208] 4A and 4B schematically show the steps of replicating the second hologram corresponding to the green channel. The position of the replication composite 44 and the base substrate 42 preferably remains unchanged. As shown in Fig. 4A, the second master hologram 6 can be translated or rotated to bring it into a desired position. In addition, a second light-sensitive layer 16 can be applied to the replication composite 44 to further build up its layer structure. The second light-sensitive layer 16 can be applied, for example, by lamination from a roll. To perform such lamination, the base substrate 42 is preferably sufficiently rigid and stably mounted. Exposure can then be achieved by directing reference beams 26 of green light onto the second master hologram 6. A green laser can be used for this purpose.The reference beams 26 are reflected by the second master hologram 6 and form object beams 28, which converge to the convergence point 40. The absolute position of the convergence point 40 is the same as for the first master hologram 4. The reference beams 26 and the object beams 28 interfere in the light-sensitive material 16 of the replication composite and form the second hologram 160. This is fixed before further exposure.

[0209] Analogously, the third master hologram 8 can be aligned according to predetermined instructions to bring it into a desired position, as shown in Fig. 5A. A third light-sensitive layer 18 can be added to the layer structure of the replication composite 44. A red laser can be used to direct reference beams 26 onto the third master hologram 8 and generate the third hologram 180 in the replication composite 44. The third hologram 180 is also fixed before further processing. The replication composite 44 thus comprises a polychromatic RGB hologram. In this way, all three color channels of the polychromatic hologram are precisely aligned with one another, as demonstrated by the identical positions of the convergence points 40 during each exposure step. This is possible despite the alignment errors in the master composite 2 using the method according to the invention.

[0210] The exposed and fixed polychromatic hologram can be delaminated from the rigid base substrate 42 to obtain a flexible polychromatic hologram, or the base substrate 42 can serve as a rigid replication substrate to obtain a stable polychromatic hologram. The rigid replication substrate can be used to position multiple polychromatic holograms on top of each other to encapsulate the replicated holograms, preferably between two rigid replication substrates.

[0211] Fig. 6 shows a method for producing a polychromatic hologram using the multilayer master composite 2 from Fig. 1. In the embodiment of Fig. 6, the same master composite can be used to expose all three photosensitive layers of the first polychromatic hologram 20. This can be done at a single workstation without having to move the replication composite 44 between exposure steps. The replication composite 44 according to Fig. 6 comprises a rigid replication substrate 43 and a first photosensitive layer 14. The replication composite 44 is preferably positioned on the surface of the master composite 2 such that the master composite 2 can move at least slightly with respect to the replication composite 44.An optical fluid 30 is introduced between the surface of the master substrate 10 and the replication substrate 43 to create optical contact between these process components. Furthermore, the adjacent surfaces of the replication substrate 43 and the master substrate 10 are provided with an anti-reflective coating. For the replication of the first master hologram 4 in the first light-sensitive layer 14, the master composite 2 or the replication composite 44 is positioned such that the first master hologram 4 is exactly above / below a desired position of the first hologram in the light-sensitive layer 14. The first master hologram 4 is then exposed. Since in this embodiment the first master hologram 4 reflects blue light, the material of the light-sensitive layer 14 is selected to be (at least) sensitive to blue light.Since the master hologram 4 performs a light-collecting function, the same light-collecting function is inscribed in the first light-sensitive layer 14. This occurs by directing one or more blue laser beams via the light-sensitive layer 14 onto the first master hologram 4. The blue laser beams are reflected by the first master hologram 4 toward a light-collecting point (focus). The reflected beams (object beams) interfere with the incident reference beam in the light-sensitive layer 14, forming a diffraction structure. The diffraction structure fulfills the same optical function as the first master hologram 4 and is considered a reflection volume hologram. In particular, the diffraction structure can convert a planar blue wavefront into a converging blue wavefront.After exposure, the light-sensitive layer 14 is cured ("bleached") using UV radiation and heat to prevent the diffraction structure from being affected by further radiation. This causes the light-sensitive layer 14 to lose its light sensitivity. Curing can take place in the same workstation as the exposure, for example, by activating a UV lamp and / or heat source.

[0212] After the first hologram has been cured in the first photosensitive layer 14, a second photosensitive layer 16 is applied to the replication substrate. Since the same master composite 2 is also used for exposing the second photosensitive layer 16, the application of the second photosensitive layer can preferably be carried out without moving the replication substrate 43. The second photosensitive layer 16 can be sprayed, printed, glued, or applied to the replication substrate 43 in some other way. To perform this step in the same workstation, a print head can be activated. Alternatively, a supply roll can provide a solid layer of photosensitive material, which is laminated to the replication composite 43 using a laminating roller.Lamination is preferably used to adhere the light-sensitive material seamlessly to the replication composite 43 without the need for an adhesive layer. The laminating roller can roll over the replication composite 43 before leaving an area where exposure takes place. This way, it does not have to interfere with the exposure light rays.

[0213] The second light-sensitive layer 16 is preferably exposed with the second master hologram 6. This is schematically shown in the upper right quadrant of Fig. 6. The second master hologram 6 can be configured such that it is located in a predetermined alignment, in particular directly above the first master hologram 4. However, small deviations from the predetermined alignment can occur, e.g. due to the manufacturing process of the master composite 2. In order to compensate for the deviations from the predetermined alignment in the master composite 2, the master composite 2 can be slightly repositioned before exposure. The repositioning is preferably designed such that the second master hologram 6 is aligned exactly above the first hologram in the layer 14 according to the predetermined alignment conditions.In this way, the alignment of the holograms in the replication array 44 can have tighter tolerances than the alignment of the master holograms one above the other in the master array 2.

[0214] In this embodiment, the second master hologram 6 is designed to reflect green light. Since the first hologram in layer 14 and the first master hologram 4 only reflect blue light, they have no effect on green light. Therefore, if a green laser is used to illuminate the second master hologram 6, it can first pass through these layers without being deflected. It is then reflected by the master hologram 6. The incident reference beam interferes with the reflected object beam in the light-sensitive layer 16, which is sensitive to green light. The second hologram is formed in this layer 16 and then cured.

[0215] A third photosensitive layer 18 is then applied to the second photosensitive layer 16. The third photosensitive layer 18 is sensitive to red light and can be exposed to the third master hologram 8 to form a third reflection hologram with a light-harvesting function. The third photosensitive layer 18 is exposed using the third master hologram 8 and then cured, as schematically shown in the lower right quadrant of Fig. 6. The result is a first polychromatic hologram 20 comprising several layers, including a replication substrate 43, a first hologram in a first photosensitive layer 14, a second hologram in a second photosensitive layer 16, and a third hologram in a third photosensitive layer 18. This is shown in the lower left quadrant of Fig. 6.The polychromatic hologram 20 can preferably collect white light to a point, so that it can be used in a very compact way as a combination of convex mirror and planar mirror.

[0216] As explained above for Fig. 2, the polychromatic hologram of Fig. 6 can also be produced analogously in different exposure stations with three master arrays. Thus, a first master array can be designed for blue light, a second master array for green light, and a third master array for red light.

[0217] Fig. 7 schematically shows the structure of a holographic-optical element consisting of six reflection holograms, which can be produced using the method according to the invention. A first polychromatic hologram 20 has the optical function of a convex mirror and can convert white light with a spherical wavefront into white light with a planar wavefront. The first polychromatic hologram 20 is produced in particular using a master composite 2, wherein the master composite 2 comprises three reflection master holograms 4, 6, and 8. The master holograms each reflect blue, green, and red light of the optical function of the convex mirror. Although the master holograms can be present in a single layer, in this embodiment they are each present in a layer of the master composite 2. In this embodiment, the polychromatic hologram 20 has the same number of hologram layers as the master composite 2.However, it is also possible according to the invention to replicate more than one master hologram in the same light-sensitive layer of a replication composite 44, so that the polychromatic layer 20 could, for example, have only two hologram layers.

[0218] In a parallel process, a second master hologram 2 with a different function is used to produce a second polychromatic hologram 22 with a different light-deflecting function. In this embodiment, the second polychromatic hologram 22 is a reflection hologram that reflects white light at a predetermined angle. Thus, the second polychromatic hologram 22 fulfills the function of a plane mirror.

[0219] Each of the first polychromatic hologram 20 and the second polychromatic hologram 22 has a non-holographic lower layer, specifically a replication substrate 43. The two polychromatic holograms 20 and 22 are stacked on top of each other, as shown in the lower right corner of Fig. 7. The replication substrate 43 is used to align the polychromatic holograms so that they are encapsulated between two outer replication substrates 43. This ensures that no rotational positioning errors occur between the two holograms 20, 22. Since the diffraction pattern of the second hologram 22 is essentially consistent in the longitudinal and transverse directions, translational displacement is less critical. The two polychromatic holograms 20, 22 are bonded together, for example, using an optical adhesive layer and / or by lamination, to create a holographic-optical element.The holographic optical element has six holographic layers, whereby the tolerances and properties of the HOE are improved compared to the master composites 2 used.

[0220] Fig. 8 shows a HOE comprising a first polychromatic hologram 20 and a second polychromatic hologram 22, each produced according to the method according to the invention. Each of the two polychromatic holograms is an RGB hologram, with the RGB holograms attached to one another in a mirrored sequence. The HOE (in particular, a "z-hologram") thus has, for example, a BGRRGB layer structure. While the first polychromatic hologram 20 was produced as shown in Figs. 3A-5B, the second polychromatic hologram 22 has a planar reflective optical function and is exposed with a planar wavefront.

[0221] The first polychromatic hologram 20 converts a spherical reconstruction wavefront 32 into a planar wavefront. A red component of the reconstruction wave from 32 is reflected by the third hologram 180 to form the red reflected rays 38. A green component of the reconstruction wave from 32 is reflected by the second hologram 160 to form the green reflected rays 36. Similarly, a blue component of the reconstruction wave from 32 is reflected by the first hologram 140 to form the blue reflected rays 34.

[0222] The second polychromatic hologram 22 then reflects the light beams 38, 36, and 34 to create the planar deflected wavefront 46. The holograms 140, 160, and 180 of the second polychromatic hologram reflect the blue light beams 34, the green light beams 36, and the red light beams 38, respectively. Thus, the planar wavefront 46 can preferably appear white. It can also have a color determined by the intensities of the reflected beams. A complex light-deflecting function can thus be performed in a precise and compact manner.

[0223] List of reference symbols

[0224] 2 Master's network

[0225] 4 first master hologram

[0226] 6 second master hologram

[0227] 8 third master hologram

[0228] 10 Master substrate

[0229] 12 Master element

[0230] 14 first light-sensitive layer

[0231] 16 second light-sensitive layer

[0232] 18 third light-sensitive layer

[0233] 20 first polychromatic hologram

[0234] 22 second polychromatic hologram

[0235] 24 HOE

[0236] 26 Reference beam

[0237] 28 Object beam

[0238] 30 optical fluid

[0239] 32 Reconstruction wavefront

[0240] 34 reflected waves of the first wavelength range

[0241] 36 reflected wave of the second wavelength range

[0242] 38 reflected wave of the third wavelength range

[0243] 40 Convergence point

[0244] 42 Base substrate

[0245] 43 Replication substrate

[0246] 44 Replication network

[0247] 46 deflected wavefront

[0248] 48 Light source / radiation source

[0249] 50 UV radiation source first replicated hologram second replicated hologram third replicated hologram

Claims

PATENT CLAIMS 1 . A method for replicating a polychromatic hologram composite, comprising the following steps: a. providing a first master hologram designed for a first wavelength range and a second master hologram designed for a second wavelength range, b. providing a replication composite with a first light-sensitive layer on a replication substrate c. exposing the first master hologram to obtain a first replicated hologram in the first light-sensitive layer using light of the first wavelength range, d. fixing the first replicated hologram in the first light-sensitive layer, e. applying a second light-sensitive layer to the first light-sensitive layer, f. exposing the second master hologram to obtain a second replicated hologram in the second light-sensitive layer using light of a second wavelength range, g.Fixing the second replicated hologram in the second light-sensitive layer.

2. Method according to claim 1, characterized in that the method comprises the following further steps: h. applying a third light-sensitive layer to the second light-sensitive layer, i. providing a third master hologram designed for a third wavelength range, j. exposing the third master hologram to obtain a third replicated hologram in the third light-sensitive layer using light of the third wavelength range, k. fixing the third replicated hologram in the third light-sensitive layer.

3. Method according to one of the preceding claims, characterized in that the first and / or the second master hologram are provided in a master composite, wherein the same master composite or a master composite with an identical configuration is used for exposing the first and second light-sensitive layers.

4. Method according to one of the preceding claims, characterized in that the exposure with the first and / or the second master hologram takes place at a first and / or second exposure station, wherein an adjustment of the position of the respective master hologram with respect to the replication composite in the longitudinal and / or transverse direction preferably takes place at each exposure station.

5. Method according to one of the preceding claims, characterized in that the first and / or second master hologram is provided in a master composite with a layer structure, wherein the first master hologram is present in a first layer and the second master hologram in a second layer and wherein the light-sensitive layers of the first replication composite are applied, exposed and fixed in a mirror-symmetrical order with respect to the layer structure of the master hologram.

6. Method according to one of the preceding claims when dependent on claim 2, characterized in that one of the first, second or third wavelength ranges corresponds to red light, one of the first, second or third wavelength ranges corresponds to green light and one of the first, second or third wavelength ranges corresponds to blue light and / or the first, second and third master hologram is a reflective hologram.

7. A method according to any one of the preceding claims, characterized in that the light-sensitive layers comprise a photopolymer, wherein the photopolymer is preferably sensitive to light of at least the first and second wavelength range.

8. Method according to one of the preceding claims, characterized in that the application of a light-sensitive layer is carried out by gluing or by lamination, wherein the lamination is preferably carried out by means of a laminating roller at 20 - 300 °C and at a pressure force between 10 - 20000 N.

9. Method according to one of claims 1 - 7, characterized in that the application of the light-sensitive layers comprises a coating of a photopolymer in liquid form and drying.

10. Method according to one of the preceding claims, characterized in that the replication substrate, the light-sensitive layers and / or the replication composite are in the form of a web of any length and / or are transported on a flow path by means of transport rollers, wherein the replication process preferably takes place continuously.

11. Method according to one of the preceding claims, characterized in that the first and / or second master hologram are provided in a master composite comprising a master substrate, wherein the master substrate is positioned on the replication substrate of the replication composite, wherein preferably an optical adhesive film or an optical liquid is applied between the master substrate and the replication substrate, wherein preferably the replication substrate and / or the master substrate is provided with an anti-reflection coating.

12. Method according to one of the preceding claims when dependent on claim 2, characterized in that steps a to k are repeated analogously to replicate a polychromatic hologram into a second replication composite using a fourth, fifth and sixth master hologram, wherein preferably the exposure of one of the two replication composites is carried out by means of a planar wavefront and the exposure of the other of the two second replication composites is carried out by means of a spherical wavefront.

13. Method according to the preceding claim, characterized in that the two replication composites are connected to one another after the replication method, wherein the replication composites are arranged at a distance of less than 1 mm, preferably less than 0.5 mm, particularly preferably less than 0.1 mm.

14. Replication composite comprising at least a first and a second replicated hologram producible by a method according to one of the preceding claims.

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