Sequential exposure of hologram stacks

Abstract

The invention relates to a method for replicating a multi-color hologram stack, comprising the steps of: providing a first master hologram configured for a first wavelength range and a second master hologram configured for a second wavelength range; providing a replica stack having a first photosensitive layer on the replica substrate; exposing the first master hologram with light of a first wavelength range to obtain a first replicated hologram in the first photosensitive layer; fixing the first replicated hologram in the first photosensitive layer; applying a second photosensitive layer on the first photosensitive layer; exposing the second master hologram with light of a second wavelength range to obtain a second replicated hologram in the second photosensitive layer; a second replicated hologram is fixed in the second photosensitive layer. The invention also relates to a replica stack comprising at least a first replica hologram and a second replica hologram, wherein the replica stack can be produced by the method according to the invention.

Description

Technical Field

[0001] This invention relates to a method for replicating a multicolor hologram stack, comprising the following steps: providing a first master hologram configured for a first wavelength range and a second master hologram configured for a second wavelength range; providing a replication stack having a first photosensitive layer on a replication substrate; exposing the first master hologram with radiation of the first wavelength range to obtain a first replicated hologram in the first photosensitive layer; fixing the first replicated hologram in the first photosensitive layer; applying a second photosensitive layer on the first photosensitive layer; exposing the second master hologram with radiation of the second wavelength range to obtain a second replicated hologram in the second photosensitive layer; and fixing the second replicated hologram in the second photosensitive layer. The invention also relates to a replication stack comprising at least a first replicated hologram and a second replicated hologram, wherein the replication stack can be produced by the method according to the invention. Background Technology

[0002] This invention relates to the field of hologram reproduction.

[0003] Holograms are generated by the interference of a reference beam with light reflected or diffracted from the surface of an object (the object beam). Traditionally, three-dimensional objects have been used to generate unique, custom holograms. Commercially available holograms, on the other hand, are typically produced using mass production replication methods. This replication method usually uses a master hologram exhibiting the diffraction pattern to be replicated. The diffraction pattern can be configured for the diffraction of radiation at a single wavelength or a narrow wavelength range (monochromatic) or multiple wavelengths (multicolor). In the case of multicolor diffraction patterns, the master hologram can be generated incrementally 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 represents a separate layer of multiple stacks. Color channels can also form separate master holograms, which are not arranged in a stacked manner but are adjacent to each other or in different workstations in the replication process. The master hologram can exist in the form of a film.

[0004] The master holograms used are typically mounted in or on a substrate body that carries the master hologram. The substrate body is preferably rigid, transparent, and can be of various shapes, such as cuboid, plate, or roller. The combination of the master hologram (or multiple master holograms) and the substrate body forms a master stack.

[0005] A master stack is exposed using a coherent light source to copy a diffraction pattern from the master hologram into a photosensitive material, which is provided, for example, in the form of layers, particularly as a stack having one or more carrier films. The photosensitive material can be sensitive to radiation within a specific wavelength range, for example, to the wavelength range of a specific color (e.g., red, green, or blue). Photosensitive materials sensitive to the entire visible spectrum are also known. For mass production, the photosensitive stack can be provided in the form of a flowing roll comprising the photosensitive material and one or more carriers or protective layers. For this purpose, the photosensitive roll is transported through various workstations to generate HOEs (holographic optical elements).

[0006] During exposure, the composite roll is brought into optical contact with the surfaces of the master sheet stack. This "optical contact" should preferably allow the light beam to pass between the processed parts without experiencing significant reflection or even total internal reflection. Direct material contact between the processed parts is possible but not required. Preferably, neither reflection (especially total internal reflection) nor scattering occurs at the interface between the surfaces of adjacent processed parts.

[0007] To create a reflection hologram, coherent light passes through the composite material before reaching the master hologram and being reflected back. The object beam and the reference beam interfere with each other in the photosensitive material to form a replicated hologram. The replication process is sensitive to variations in exposure angle, intensity, wavelength, etc., which must be adjusted according to the optical properties of the master hologram. Typically, exposure is performed on each master hologram according to a set of pre-programmed parameters.

[0008] HOE (Holographic Optical Element) generally refers to an optical component in which holographic properties are used to achieve specific beam paths of light, such as transmission, reflection, diffraction, scattering, and / or redirection. This allows the desired optical function to be implemented in a compact manner on any substrate. The holographic properties preferably utilize the wave properties of light, particularly coherence and interference effects. Both the intensity and phase of the light are considered.

[0009] For example, HOEs can be configured to perform the optical functions of classic optical components such as lenses or mirrors. However, due to their thin structure, they can be much more compact than conventional optical components. They can also be designed to avoid known optical errors of conventional optical components, such as spherical aberration and chromatic aberration. For example, an HOE can convert a plane wavefront into a spherical wavefront and vice versa. They require very little space and can be easily integrated into surfaces such as windows, eyeglasses, cards, or other product surfaces. In order to perform optical functions without the optical errors of conventional components, HOEs must be efficient, and all channels must be precisely aligned with each other. However, known techniques used to create HOEs often result in quality and / or alignment errors.

[0010] For some applications, it may be desirable to expose HOEs in a multi-layered manner or with multiple superimposed patterns or wavelengths (e.g., color channels). In some cases, holograms can contain multicolor diffraction patterns in the form of Bragg gratings with different frequencies within a single layer of material. Such holograms can be recorded simultaneously with multiple wavelengths, for example, as RGB or CMY holograms. Multicolor holograms can be replicated from multicolor RGB or CMY master holograms, which can be single-layered or stacked holograms with different wavelengths. This will require the use of photosensitive materials that are sensitive to all color channels used. However, such materials are typically equally sensitive to all wavelengths and may not provide the highest image resolution across the entire wavelength range. Furthermore, the quality of the resulting multicolor hologram is limited by the quality of the master stack from which it replicates the multicolor hologram. If the various holograms, layers, and / or channels of the master stack are not precisely aligned with each other, alignment errors are replicated into the photosensitive material. Depending on the production method used, these errors may even be amplified further. This can severely limit the positional accuracy of the replicated multicolor hologram.

[0011] As described below, it is known in the prior art that multiple channels of a master hologram are formed by creating master holograms individually, and then stacking the master holograms on top of each other. The lamination process typically deforms the layers and changes their positions relative to each other, causing the channels to no longer be perfectly aligned. If the channels are "multiplexed" (or stacked) within a single photosensitive layer, the exposure of the different channels must also be perfectly coordinated. This is difficult to achieve in practice. If multiple master holograms are generated in a single layer as multiplexed holograms, the lamination step can be omitted when arranging the master holograms on top of each other. This avoids the errors associated with uneven deformation of the layers, which in some cases makes multiplexed master holograms superior to stacked master holograms. On the other hand, although multiplexed holograms have slightly better positioning accuracy, they are less efficient than stacked holograms in terms of diffraction radiation.

[0012] Multicolor holographic elements can also comprise multiple holograms that can be stacked one on top of the other. For example, a holographic element can display multiple superimposed monochromatic holograms that have been individually recorded and combined into a stack. This allows for the use of photosensitive materials specifically configured for particular wavelengths or color channels and improves the quality of the HOE.

[0013] Such holographic elements are used in many fields, such as transparent displays (e.g., in shop windows, refrigeration units, and car windows), lighting applications, such as information or warning signals in glass surfaces, and photosensitive detection systems, such as for interior monitoring (eye tracking in vehicles or tracking the presence of people indoors).

[0014] For example, DE102021116146A1 discloses a multicolor hologram comprising six layers in a single stack. These layers are configured for different wavelengths. The three upper layers can form a first holographic element configured to convert an upward-facing spherical wavefront into a downward-facing plane wavefront by reflecting light from the blue, green, and red portions of the electromagnetic spectrum at a predetermined angle. The three lower layers can form a second holographic element configured to reflect the downward-facing plane wavefront upward to generate a plane wavefront at a predetermined angle. In this way, the layers of two holographic elements can be used as a combination of a convex mirror and a plane mirror. Advantageously, the arrangement of two holographic elements arranged adjacent to each other, configured to at least partially reflect light, allows for high refractive power while providing high image quality and a compact structure.

[0015] However, precise positioning of the holographic layers relative to each other is essential to avoid undesirable filter effects and ensure optical functionality. In the case of multilayer holograms, the correct positioning of the stacked holograms relative to each other is crucial to the quality of the generated HOE. Depending on the complexity of the HOE, the number of layers in such a stack can increase, posing considerable challenges during the adjustment steps of its production.

[0016] In an exemplary production method, a single photosensitive composite roll travels through various stations of the replication method, where replication for different master stacks configured for specific color channels occurs at their respective stations. The composite roll may include a photosensitive layer in which the master holograms for the color channels are replicated at their respective stations. To achieve perfect positioning of the holograms replicated in the composite roll, the flowing composite roll must slow down at precise locations at each station. This is extremely difficult to do with high repeatability due to the deformable nature of the composite roll. This introduces alignment errors, exceeding any alignment errors in the master stacks used for replication, into the multicolor holograms.

[0017] Alternatively, the composite roll can also be exposed at a single workstation providing the master stack. Exposure can be performed simultaneously or sequentially for each desired wavelength. The flowing composite roll only needs to be slowed down once during exposure, which reduces the risk of errors due to misalignment and / or distortion. However, errors in the relative positioning of the layers in the master hologram are reproduced in the composite roll. For example, layers of individual color channels in the master stack may exhibit distortion or shift due to the exposure or integration process, which particularly adversely affects the optical functionality of complex HOEs. The prior art does not provide any solution for correcting positioning errors in the master stack when a master stack has already been created. Instead, these errors are reproduced in the replicated hologram.

[0018] Another alternative is to generate each layer of the HOE master stack using a single layer of photosensitive material within its respective composite roll, and then combine the individual layers of the composite roll into a stack. This prevents the reproduction of positioning errors in the master stack. However, this also introduces new errors. Due to technological limitations, the placement, lamination, and bonding of layers are performed within tolerances, which are added together when the steps are repeated to generate stacks with two, three, four, or more layers. Furthermore, adhesive layers may be required between the individual holograms to create the layer structure. This can increase the overall thickness of the layer structure, making it difficult to embed the HOE into the part.

[0019] JPH11272153A discloses the use of position markers to align different layers of a hologram stack. According to this paper, multilayer holograms are generated from multiple layers of photosensitive material. Holograms with different properties are recorded in each layer of photosensitive material, and position markers are holographically recorded in each of the multiple holographic layers. Position markers are then used to align the layers on a substrate and laminate them together.

[0020] This is a complex process. Furthermore, the lamination process itself can lead to alignment errors, for example, due to varying degrees of deformation of the layers. Additionally, the number of layers required to form a multicolor hologram is high, and there are no known methods for altering the layer structure of the product compared to the stacking of the master templates used.

[0021] Depending on the intended use of the multicolor hologram, it may be desirable to change not only its positioning tolerances but also its thickness relative to the master stack. For example, in applications with a high risk of wear, it may be desirable to reduce the number of layers in the multicolor hologram that may separate from each other. Similarly, when embedding a multicolor hologram in a very thin product such as a holographic contact lens, reducing the total thickness of the multicolor hologram compared to the master stack may also be desirable. Therefore, it may be advantageous to generate multicolor holograms that exhibit a different layer structure or total thickness compared to the master stack, as well as improved positioning accuracy.

[0022] Another approach to improving the positioning tolerance of replicated multicolor holograms is to select a master stack with a lower risk of positioning errors, for example, by making the master stack include all master holograms reused as a single layer. This also has the advantage of achieving a lower total thickness of the replicated stack by replicating the master holograms as reused as a single layer of the replicated stack. However, such reused holograms may suffer from lower efficiency compared to multilayer holograms. Therefore, it is desirable to provide a technical solution that, depending on the desired application, ensures the required efficiency of the replicated multicolor hologram as a total thickness while simultaneously minimizing positioning tolerances.

[0023] Master stacks are also susceptible to further errors and quality defects that occur during their production or lifespan. For example, multiplexed holograms or various monochrome master holograms within a master stack may expand or shrink due to their production methods. This can cause a shift in the actual wavelength or angle at which the master hologram is most effectively exposed. This shift is often wavelength-dependent. For instance, the red channel in a multiplexed hologram or a red master hologram layer may experience a larger shift in optimal exposure parameters than the green channel or a green master hologram layer. When all channels of a master stack are copied simultaneously, the copying parameters (e.g., the exposure angle of an RGB laser) can be shifted uniformly across all channels. However, this is not ideal, as different channels may have different deviations from their target parameters. Copying such master stacks typically results in inefficient and low-quality reproduced holograms. Therefore, a technique is needed that can improve the efficiency and quality of reproduced holograms compared to master stacks.

[0024] Therefore, there is a need for alternative methods that can be used to generate multicolor holograms with high positional accuracy.

[0025] DE102010014305 A1 discloses a method for generating copies of volumetric reflection holograms. For this purpose, a holographic film is laminated onto a roller having at least two (polygonal) master surfaces, which are then brought into contact with and exposed to at least one master hologram. One or more master surfaces can be simultaneously exposed to laser over a large area. The roller rotates uniformly or incrementally during exposure. This aims to improve productivity, even when generating large-area reflection holograms. No application of the method for generating multicolor holograms is disclosed.

[0026] The purpose of this invention

[0027] The object of this invention is to provide a method capable of replicating multicolor holograms without the drawbacks of prior art. In particular, one object of this invention is to provide a method for replicating multicolor holograms, wherein multiple color channels or patterns with different wavelengths can be positioned relative to each other in a holographic element using simple means, in a repeatable manner, and with high precision. Furthermore, another object of this invention is to modify, and particularly improve, the properties of the replicated multicolor hologram compared to the nature of stacking one or more master holograms. Summary of the Invention

[0028] This objective is achieved through the features of the independent claim. Advantageous embodiments of the invention are described in the dependent claims.

[0029] In a first aspect, the present invention relates to a method for replicating multicolor hologram stacks, comprising the following steps:

[0030] a. Provide a first master hologram configured for a first wavelength range and a second master hologram configured for a second wavelength range.

[0031] b. Provide a replication stack with a first photosensitive layer in / on the replication substrate;

[0032] c. Expose the first master hologram using radiation within a first wavelength range to obtain a first replicated hologram in the first photosensitive layer.

[0033] d. Fix the first replicated hologram in the first photosensitive layer.

[0034] e. Apply the second photosensitive layer onto the first photosensitive layer.

[0035] f. Expose the second master hologram using radiation in the second wavelength range to obtain the second replicated hologram in the second photosensitive layer.

[0036] g. Fix the second replicated hologram in the second photosensitive layer.

[0037] Applying a second photosensitive layer on top of the first photosensitive layer after the first photosensitive layer has been exposed and fixed allows for the incremental construction of multicolor holograms during the replication process. This incremental construction makes it possible to modify, and particularly improve, the characteristics of the replicated multicolor holograms relative to the characteristics of the master hologram. Each layer of the replication stack can be advantageously exposed individually with different parameters without affecting previously exposed layers. Therefore, the exposure parameters between layers can be varied. The varying parameters can be, for example, the wavelength of the exposed radiation. Thus, each photosensitive layer of the replication stack can include a diffraction structure that redirects radiation across different wavelength ranges. In this way, under optimal exposure conditions, different diffraction structures with different wavelength characteristics can be constructed one on top of the other. This enables the creation of multicolor holographic images, particularly high-quality panchromatic images. Furthermore, the light redirection function can be guaranteed for large areas of the electromagnetic spectrum, for example, for redirecting light from the entire visible spectrum.

[0038] Variations in exposure parameters between photosensitive layers can also be used to compensate for errors or inefficiencies in different master holograms or color channels of the master stack. For example, positional errors in channels or master holograms of the master stack can be compensated for in the photosensitive layers during exposure, as described below, without affecting other layers of the replication stack. This means that the replication stack can be essentially free of known positioning errors of the master stack. The incremental construction of the replication stack makes it possible, in particular, to move the master stack slightly and precisely between exposure steps, so that the second and subsequent holograms are precisely positioned above the first exposed hologram.

[0039] The method according to the invention is an advantageous alternative to known methods, wherein individual holograms are exposed separately and subsequently joined together. In particular, the method according to the invention eliminates the need to stack and laminate the individual layers after they have been individually exposed. This avoids alignment errors typically caused by subsequent stacking and lamination.

[0040] This invention also utilizes the fact that new layers of photosensitive material can be applied to each other with greater positional tolerances than individually generated holographic layers. This is because these layers have not yet been exposed with the hologram, and their optical properties are largely uniform. The positioning of the new photosensitive layer (such as a second and any other photosensitive layer) relative to already exposed and fixed layers is not critical. It can withstand much larger tolerances than applying one exposed holographic layer to another. Therefore, this invention enables the use of a quick and inexpensive means of applying a second photosensitive layer to a first photosensitive layer.

[0041] By sequentially applying and exposing a second (and optionally further) photosensitive layer, each new layer of the multicolor hologram can be exposed with very precise alignment relative to the already exposed layers. 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 in the replication system and fixed in place such that ideal alignment of the first and second holograms is achieved in the replication system when they are brought under their respective master holograms. Unpredictable deformation or displacement of the photosensitive material that often occurs during lamination can be avoided.

[0042] Alternatively or additionally, the position of the second master hologram can be configured during exposure step (f) such that it matches the position of the already exposed first master hologram. The second master hologram can be slightly rotated and / or translated to precisely align it with the existing position of the first hologram. When the second master hologram is present in a stack within a layered structure containing the first master hologram, its position can preferably be adjusted by rotating and / or translating the entire master stack. Adjustments can also be performed if the second master hologram exists in a separate master stack and / or a separate exposure station. This adjustment of the position of the second master hologram improves the alignment of holograms on top of each other in a replication stack without material deformation or displacement, which is typically the case in lamination. In all cases, the first and second holograms can be aligned and exposed relative to each other with very tight tolerances. This avoids the introduction of alignment errors when stacking holograms. Furthermore, multicolor holograms can be generated with even tighter positional tolerances than master stacks.

[0043] The method according to the invention allows for easy correction of alignment errors in the master stack during replication. Since the master stack is typically robust, it can be rotated or translated with high precision as needed. Therefore, the master stack can be moved between steps c and e to compensate for alignment errors between the first and second master holograms. Consequently, the replication stack can advantageously exhibit tighter tolerances than the master stack.

[0044] To replicate two master holograms in a replication stack, the first and second master holograms preferably exist within a single master stack. In this variation, the first and second master holograms are preferably exposed in the same workstation, thus avoiding movement of the replication stack between exposure steps. The first and second master holograms are preferably stacked one on top of the other. The first and second master holograms can also exist as multiplexed within a single layer. The incremental construction of the replication stack in this arrangement has the advantage that each photosensitive layer can be exposed with different exposure parameters. This means that the first photosensitive layer can be exposed with first exposure parameters such as wavelength, exposure angle, and / or exposure intensity. After the first hologram has been fixed in the first photosensitive layer, a second photosensitive layer can be applied and exposed with different exposure parameters. For example, the second photosensitive layer may include a different photosensitive material and / or a different thickness than the first photosensitive layer. The second photosensitive layer can be exposed with different wavelengths, exposure intensities, and / or exposure angles. The choice of different exposure parameters can depend on the type of each master hologram (transmission hologram or reflection hologram), its configuration for a specific wavelength range, its efficiency, its alignment, its degradation, and / or the wavelength-dependent radiosensitivity of the photosensitive material.

[0045] Changing exposure parameters is useful, especially if the master stack has undergone wavelength-dependent shrinkage / expansion. Wavelength-dependent shrinkage in one channel of the master stack can be advantageously compensated for independently of other channels in the photosensitive layer. Therefore, the wavelength range and / or illumination angle of each photosensitive layer in the replication stack can be adjusted according to the degree of relevant shrinkage. In this way, exposure can be performed efficiently despite quality loss in the master stack.

[0046] This can be achieved by exposing the photosensitive layer at a slightly off-center exposure wavelength (preferably up to 50 nm, particularly up to 25 nm). The exposure wavelength may deviate from the theoretical target exposure wavelength of the currently exposed (second) master hologram or from the target exposure wavelength of the already exposed first (or other) master hologram. There may also be a deviation between the exposure wavelength of the second master hologram and the exposure wavelength of the first master hologram, which is preferably greater than the deviation required to compensate for shrinkage / expansion.

[0047] Contraction (or expansion) can also alter the optimal exposure angle of the master hologram according to the wavelength. Therefore, the exposure angle can also deviate from the target exposure angle of the respective master hologram to increase the exposure efficiency of a particular photosensitive layer. This can compensate for efficiency losses due to degradation of the master hologram. Preferably, this deviation of the exposure angle is up to 3°, particularly up to 1°. Furthermore, the exposure angle of the second master hologram may deviate from the exposure angle of the already exposed master hologram. In this case, the deviation may be larger, allowing different holographic patterns to be seen from different viewing angles. Other layers in the replication stack do not need to be affected by this. Alternatively or additionally, the exposure intensity can be adjusted between exposure steps, particularly to maintain optical balance between different channels.

[0048] By exposing the copy stack (in multiplexing or across multiple layers) with a master stack comprising more than one master hologram, the copy stack does not need to be moved between exposure steps. This allows a second photosensitive layer to be applied to the first photosensitive layer without separating or moving the copy stack from the master stack. Conversely, the application of the second photosensitive layer can also be performed in situ within the exposure station. Since the copy stack does not need to be moved from the exposure station to the coating station or another exposure station, it does not need to be precisely decelerated to determine its position in the longitudinal direction. This eliminates the risk of positioning errors in the longitudinal direction of the copy stack, further increasing the reliability of positioning.

[0049] To replicate two master holograms into a replication stack according to another preferred variation of the method, the replication stack with the first replicated hologram can be moved from a workstation containing the first master hologram to another workstation containing the second master hologram. The movement of the replication stack can be performed with very tight tolerances in the longitudinal direction, and essentially without any rotation or displacement in the lateral direction. The former can be achieved through a precise braking mechanism, and the latter through the mechanical design of the transport unit itself, such as transport rollers or a conveyor belt with precisely adjustable width. Precise adaptation of the width of the transport rollers to the width of the replication stack preferably mechanically prevents rotation or displacement of the replication stack in the lateral direction. Steps e to g are then preferably performed. During this process, the second master hologram can preferably remain fixed in place. The position of the second replicated hologram in the second photosensitive layer preferably does not rotate or translate in the lateral direction, particularly relative to the first replicated hologram.

[0050] Therefore, multicolor holograms can exhibit lower tolerances than multicolor master stacks that include master hologram stacks. The alignment characteristics (particularly rotational alignment and position in the lateral direction) of the replica stack can be improved compared to master holograms. Additional exposure parameters can also be changed between the exposure steps of the first, second, and subsequent photosensitive layers, particularly to improve the quality of the multicolor holograms.

[0051] This invention also benefits from the adhesive properties of the photopolymer layer on the carrier layer. This can result in particularly thin multilayer multicolor holograms. Referring to prior art multilayer multicolor holograms, three individually exposed holograms are assembled into a stack, each hologram in the stack typically including a photosensitive material encapsulated between two carrier layers. Additional adhesive layers are added between the carrier layers of the first and second holograms and between the carrier layers of the second and third holograms to form the stack. The layer structure according to the prior art can, for example, include: polycarbonate - photopolymer 1 with a 1° hologram - polycarbonate - adhesive - polycarbonate - photopolymer 2 with a 2° hologram - polycarbonate - adhesive - polycarbonate - photopolymer 3 with a 3° hologram - polycarbonate. A total of 11 layers are required to form the stack. This results in a greater thickness, which can make it difficult to carefully embed into products. On the other hand, it has been found that various photosensitive materials can be applied to a transparent carrier film such that they remain stable throughout their entire lifespan. The additional carrier layer and adhesive layer between the holograms can be omitted. In this way, simplified, thinner layer structures can be created. A multicolor hologram with three channels according to the invention can be constructed, for example, as follows: polycarbonate-photopolymer 1-polycarbonate-photopolymer 2-polycarbonate-photopolymer 3-polycarbonate. An 11-layer structure can be reduced to a 7-layer structure.

[0052] In the context of this invention, a "method for reproducing a hologram" or "reproduction method" is preferably a method in which the diffraction pattern of an object (particularly a master hologram) is recorded in a photosensitive material. This includes at least the exposure of individual master holograms, but may also include further preferred steps such as fixing or cutting.

[0053] In the context of this invention, a "master hologram" is preferably a holographic optical element comprising at least one hologram to be reproduced. The master hologram is configured for optical functions (e.g., diffraction, reflection, transmission, and / or refraction) at one or more wavelengths within a wavelength range. The master hologram can be, for example, a diffractive optical element (DOE). A diffractive optical element (DOE) uses a surface undulation profile with microstructures for its optical functions. Alternatively, the microstructures may also exist in the volume of the element as localized differences in refractive index. Such a master hologram is considered a so-called "volume hologram." Light transmitted through the DOE can be converted into virtually any desired distribution through diffraction and subsequent propagation. This can be an image, a sign, text, a light refraction pattern, etc. Furthermore, the master hologram can be a technical hologram, such as a Bragg mirror, a diffuser, or a hologram used as a lens.

[0054] "Configuration of the master hologram for a wavelength range" preferably means that the diffraction structure of the master hologram is configured for diffraction of electromagnetic radiation having wavelengths within 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 specifically means that the diffraction conditions provided by the first master hologram are preferably given only for light in the first wavelength range. Radiation of other wavelengths is preferably not diffracted. This also applies to the wavelength selectivity of the second master hologram, according to which diffraction should selectively occur for radiation with wavelengths within the second wavelength range.

[0055] According to the present invention, the first wavelength range and the second wavelength range are not the same. In a preferred embodiment, the first wavelength range and the second wavelength range may represent non-intersecting ranges and substantially do not exhibit intersection. For example, this may be the case if the first wavelength range and the second wavelength range correspond to different colors. For example, the first wavelength range may correspond to one color (e.g., blue, red, or green), while the second wavelength range corresponds to another color.

[0056] In the context of this invention, "wavelength range" can essentially include wavelengths of light or radiation, such as those emitted by a monochromatic laser.

[0057] In the case of a reflection hologram, the hologram can be configured such that an electromagnetic beam within the wavelength range is diffracted, causing a first-order diffracted beam to return to the replication stack. The first-order diffracted beam can interfere with a reference beam in the replication stack. 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 an electromagnetic beam within the wavelength range is diffracted, causing the diffracted beam to interfere with a reference beam in the replication stack. Electromagnetic beams with wavelengths outside the wavelength range can preferably be transmitted without diffraction. Therefore, the master hologram preferably diffracts radiation of its configured wavelength.

[0058] In the context of this invention, a "master stack" is preferably a multilayer stack comprising at least one master hologram. Preferably, the master stack comprises at least a first master hologram and a second master hologram in a layered structure. The master stack may preferably include additional layers, such as one or more caps and / or a master substrate, such that the master hologram (or master hologram) is preferably present between the master substrate and the cap. The master hologram is preferably laminated to the surface of the master substrate. The master stack is preferably rigid. The rigidity of the master stack can be ensured by the master substrate. Preferably, all layers of the master stack are firmly bonded to each other. The "master stack" can be arranged within a master element, wherein, in a preferred embodiment, the master element comprises a master stack and a substrate. Preferably, the master stack is movable relative to the substrate.

[0059] The “master element” preferably includes at least one master hologram and supports the creation of mechanical and / or optical contacts between the respective master holograms and the photosensitive layer or replication stack without damaging the master hologram. The master element preferably includes a master substrate on which at least one master hologram is present. Preferably, the master element further includes a substrate, wherein the master substrate is movably mounted relative to the substrate. The substrate is preferably aligned to contact the replication stack. Preferably, the master element further includes an alignment module for moving the master substrate (and thus the master hologram) relative to the substrate.

[0060] The “master substrate” is preferably a three-dimensional unit comprising a master hologram in a form that enables its processing and mobility. The shape of the master substrate is, in principle, unrestricted. In particular, the master hologram is held in a fixed position by the master substrate such that any movement of the master substrate directly results in a corresponding movement of the master hologram. The master substrate can be prismatic, particularly cylindrical. This can be particularly advantageous if the master substrate carries only one master hologram, where the exposure steps of the method are performed using different master stacks. It is also preferable that the master substrate exhibits a cuboid or plate shape, especially if the master substrate carries multiple master holograms, where the multiple exposure steps of the method are performed using the same master stack. Preferably, the length and width of the master substrate substantially correspond to the length and width of the master hologram. Preferably, the master substrate is at least two times, preferably five times, and particularly preferably at least twenty times the length of the master hologram. The master substrate preferably has a regular shape that allows for a tessellated or linear arrangement.

[0061] The master substrate is preferably a transparent plate, preferably made of optical glass or plastic. Master holograms can be laminated onto the surface of the master substrate to form a master stack. In some preferred embodiments, the master stack may also include a transparent top cover for protecting one or both master holograms located between the cover and the master substrate. Preferably, the top cover is also transparent. The top cover may be, for example, a transparent film or a glass layer.

[0062] In the context of this invention, the term "transparent" or "transparency" preferably refers to the property of a material in which it is substantially transmissive to light. Preferably, in the context of this invention, transparent materials are transmissive to at least a portion of the electromagnetic spectrum, preferably at wavelengths between 200 nm and 25 μm, and particularly preferably between 400 nm and 780 nm. Particularly preferably, transparent materials, such as transparent master substrates or transparent covers, are capable of transmitting radiation within the wavelength range exposed to the master hologram. Transparent materials can also be colored to select one or more specific wavelengths of radiation.

[0063] Preferably, the surface or cover of the master stack comprises glass, PC, TAC, or PMMA. The surface material may be in the form of a film or plate to protect the master hologram. However, the surface or cover material may also be the material of the master substrate itself and may, for example, be in the form of a cuboid or cylindrical shape.

[0064] In a preferred embodiment, the master element comprises a master stack and a substrate, wherein the master stack and the substrate are mounted so as to be movable relative to each other. This solution allows one substrate of the master element to remain stationary while the other substrate rotates or translates. Preferably, the substrate remains stationary while the master substrate (and therefore the master hologram) moves. In this way, the replication stack can maintain constant contact with the surface of the master element without friction or deformation between exposure steps due to relative movement at the interface. Direct contact between the replication stack and the moving mechanical parts of the master element (master stack) is avoided, thus also avoiding the risk of mechanical deformation of the replication stack. Simultaneously, the master stack can move freely relative to the substrate (and therefore also relative to the replication stack) to compensate for any positioning errors in the master stack. Furthermore, the replication stack does not need to be maintained at a certain distance from the master element, which could lead to efficiency losses during exposure. Instead, the mechanical contact between the replication stack and the substrate ensures optimal optical contact, thereby minimizing optical losses at the interface between the replication stack and the master element.

[0065] In the context of this invention, the "substrate" is preferably a three-dimensional unit configured to mechanically contact the replica stack. Preferably, the substrate is rigid, allowing one or more layers to be laminated onto it. The substrate is preferably mounted in a fixed manner, while the master stack is preferably mounted in a manner movable relative to the substrate. The substrate preferably has optical and mechanical properties similar to those of the master substrate. The substrate is particularly transparent, preferably made of optical glass or plastic. The shape and size of the substrate can be similar to, and preferably exceed, the shape and size of the master stack, such that the master stack remains completely covered by the substrate in all positions of rotation and translation. For example, the length and / or width of the substrate can be at least 110%, preferably at least 120%, or even better, at least 130% of the length and / or width of the master stack.

[0066] In the context of this invention, "replication stacking" preferably refers to a multilayer material comprising at least one photosensitive layer. The photosensitive layer preferably comprises a photosensitive material, such as silver halide, two-color gelatin, photoresist, photopolymer, photochromic material, photothermoplastic, LiNbO3, Bi... 12 SiO 20 The photosensitive layer can be a CCD or a combination thereof. The photosensitive layer can be sensitive to electromagnetic radiation over a wide wavelength range. For example, the photosensitive layer can be sensitive to electromagnetic radiation in both a first wavelength range and a second wavelength range. Alternatively, the first photosensitive layer can be sensitive to electromagnetic radiation only in the first wavelength range, and the second photosensitive layer can be sensitive to electromagnetic radiation only in the second wavelength range. Any number of photosensitive layers can be provided, such as two, three, or more, wherein the sensitivity of the layers may overlap or not overlap as needed within the wavelength range. Preferably, the replication stack includes at least one, preferably two, outer carrier films, wherein the carrier films are preferably transparent to electromagnetic radiation of all wavelengths to which the replication stack is to be irradiated. The photosensitive layer can be in the form of a composite roll. In a preferred embodiment, the replication stack can also be in the form of a composite roll. The replication stack may include a replication substrate, which is preferably in direct contact with the photosensitive layer or with another intermediate layer.

[0067] Applying a second photosensitive layer to the first photosensitive layer of the replication stack preferably results in the photosensitive layer layer structure being on top of or above each other in the replication stack. After exposure and fixation, the replicated first hologram and the replicated second hologram are preferably also arranged vertically above each other in the layer structure. In a preferred embodiment, an additional photosensitive layer may be applied to the first two photosensitive layers or holographic layers.

[0068] During the process according to the method of the invention, the photosensitive layer may lose its photosensitive properties, for example, by fixation. For simplicity, related layers in the replication stack are still referred to as photosensitive layers even if they no longer respond to the incident light beam. Those skilled in the art will know which layers this means, especially since they are still based on the same photosensitive material. In some paragraphs, the photosensitive layer is referred to as a holographic layer or holographic layer after exposure.

[0069] In a preferred embodiment of the invention, the exposed replica stack is pre-fixed after exposure and before the moving exposed replica stack. Pre-fixing can sufficiently stabilize the exposed photosensitive layers to carry them to another processing station, particularly a fixing station, without affecting the already replicated hologram. This is particularly advantageous for replica stacks comprising liquid or soft photosensitive layers. It is also preferable that the replicated multicolor hologram is fully fixed after all exposure steps, regardless of the number of layers. Full fixation can be performed in situ, particularly in the exposure station, without moving the replicated multicolor hologram. Alternatively or additionally, full fixation can be performed in a downstream fixing station. This fixation can be performed on the stationary replicated multicolor hologram or while the replicated multicolor hologram is being transported through the fixing station. The latter can achieve a uniform dose of UV radiation and / or heat on the replicated multicolor hologram while using a device with lower power.

[0070] In the following preferred embodiments, "fixing" preferably refers to the final step of completely fixing, pre-fixing, or fixing a pre-fixed photosensitive material.

[0071] In the context of this invention, "fixation" preferably refers to the treatment of the photosensitive material to reduce its sensitivity to further exposure to further electromagnetic radiation and / or mechanical effects. Fixation can also be configured to adjust the material properties of the photosensitive material, particularly by reducing its viscosity and / or by converting the material into a semi-solid or solid form. It is likely preferred to use fixation on a replicated stack of already exposed photosensitive layers to stabilize the photosensitive material and prevent further exposure of the grating. The same methods as full fixation can be used for pre-fixation, particularly UV irradiation and heat treatment. It is likely preferred to adjust the method parameters used for fixation, such as the intensity of UV radiation or the temperature of the heater, to achieve desired mechanical properties and / or a desired low photosensitivity.

[0072] If the replication stack comprises two or more holograms configured for different wavelength ranges, then in the context of this invention, the replication stack is preferably a multicolor hologram. The presence of a replication substrate in the multicolor hologram is optional.

[0073] In the context of this invention, a "replication substrate" is preferably a component located between one or more photosensitive layers and a master stack during exposure. The replication substrate preferably provides optical contact between the master stack and the photosensitive layers, and preferably also protects the photosensitive layers from mechanical damage. In a preferred embodiment of the invention, the replication substrate is another film-like layer, such as a protective layer, a flexible underlayer, or a carrier layer. It can be used to process the replication stack, for example, by bringing it to a master element and integrating it into the final product, wherein the replication substrate can be removed during integration. In another preferred embodiment of the invention, the replication substrate is rigid, and a portion of a composite roll comprising one or more photosensitive layers is laminated onto the replication substrate to create a stable replication stack. Such a replication substrate can have properties similar to the master substrate and / or the substrate, and can be used as a substitute for the substrate. Preferably, the rigid replication substrate is in the form of a plate. An advantage of this embodiment is that the rigid replication substrate can be transported together with the remainder of the replication stack to a further processing station in the production process. This may be preferred where the production of a series of multicolor holograms, each constructed on a rigid replication substrate, is desired for subsequent processing of the multicolor holograms. For example, rigid replication substrates can be used to precisely mechanically position multiple multicolor holograms vertically and encapsulate them between substrates. When multiple multicolor holograms are stacked on top of each other, the rigidity of the replication substrate reduces the risk of unwanted deformation or displacement. This avoids positioning errors typically caused by lamination.

[0074] In the context of this invention, "composite roll" is preferably a composite material whose length is at least twice, preferably at least five times, and even more preferably at least twenty times its width. The thickness of the composite roll is preferably adjusted to exhibit a certain degree of flexibility, allowing it to be supplied, for example, as a roll. Preferably, the composite roll exhibits a thickness of up to 300 μm. The composite roll includes a photosensitive material. Preferably, the composite roll encapsulates the photosensitive material between two transparent carrier films having a refractive index similar to that of the photosensitive material. Preferably, the refractive indices of the carrier films and the photosensitive material are between 1.4 and 1.6. The photosensitive material can be, for example, a photosensitive photopolymer or a two-color gelatin. The photosensitive material can be photosensitive across the entire visible spectrum or wavelength selective.

[0075] In the context of this invention, "exposure" is preferably understood to mean directing an electromagnetic beam onto a corresponding sensitive surface, preferably for forming a hologram. Various methods for exposing holograms are known, including transmission or reflection techniques for generating volumetric holograms.

[0076] Volume holograms are preferably written into the sensitive layer by the interference of two beams (the so-called reference beam and the object beam). Preferably, the volume hologram is written into a replication stack. This can preferably be done using transmission or reflection techniques. The interference between the object beam and the reference beam within the hologram volume preferably generates a series of Bragg planes. Thus, the volume hologram preferably exhibits a non-negligible extension in the direction of beam propagation, where the Bragg condition applies to the reconstruction of the volume hologram. For this purpose, the volume hologram exhibits wavelength and / or angular selectivity. The ability of the volume hologram to store multiple images simultaneously makes it particularly possible to generate color holograms. Light sources emitting the three primary colors blue, green, and red can be used to record the holograms. The three beams preferably expose a portion of the replication stack simultaneously at the same angle. After exposure, the three holograms are simultaneously stored in the volume hologram. To reconstruct the multicolor hologram, advantageously, each partial hologram can be reconstructed by recording only its color. Thus, assuming the color components are correctly weighted, the three reconstructed color separations overlap to form a color image that is true to the original image.

[0077] Exposure can preferably be performed via an exposure module that presents one or more light sources for this purpose. The light source is also referred to as a "radiation source" because the invisible range of the electromagnetic spectrum can also be used for holographic generation. For this purpose, the light source or radiation source preferably emits electromagnetic radiation within a first and / or second wavelength range. Preferably, the light source emits a coherent beam. Coherence preferably refers to the characteristics of light waves, thereby establishing a fixed phase relationship between two wave trains. Due to the fixed phase relationship between the two wave trains, spatially stable interference patterns may occur. Regarding coherence, a distinction can be made between temporal and spatial coherence. Spatial coherence is primarily a measure of the fixed phase relationship between wave trains perpendicular to the propagation direction and is given, for example, for parallel beams. Temporal coherence is primarily a fixed phase relationship between wave trains along the propagation direction and is given particularly for narrow bands (preferably monochromatic beams).

[0078] The coherence length preferably refers to the maximum path length difference or runtime difference between two beams starting from the origin, such that a stable interference pattern (spatially and temporally) is still generated when they overlap. The coherence time preferably refers to the time required for light to travel the coherence length.

[0079] In a preferred embodiment, the light source includes a laser. Particularly preferred are narrow-band, preferably monochromatic lasers having a preferred wavelength within the visible light 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. The laser can be selected to emit light of a specific wavelength or wavelength range. This can be achieved by selecting a laser made of suitable materials. For example, ruby ​​lasers, He-Ne lasers, Ar⁺ lasers, Kr⁺ lasers, He-Cd lasers, and / or Nd lasers can be used. 3+ YAG lasers. These or other types of lasers can be combined with optical parametric oscillators to generate coherent beams of different wavelengths. Lasers with different wavelengths can also be combined, for example, to generate RGB lasers.

[0080] Different types of lasers, particularly solid-state lasers, can be combined with optical parametric oscillators (OPOs) to generate coherent beams of different wavelengths as tunable systems. The OPO preferably comprises an optical resonator and at least one nonlinear optical crystal. Preferably, and particularly, a system with multiple converter crystals can be used, employing three-wave mixing (f_pump = f_signal + f_idler). By changing the frequencies of f_signal and / or f_idler, laser wavelengths can be generated over a very wide wavelength range. This particularly includes the entire visible and infrared range of the electromagnetic spectrum.

[0081] Other light sources can also be used, with coherent light sources being preferred. Narrow-band light sources are preferred, and monochromatic light sources are preferred, including, for example, light-emitting diodes (LEDs), which may be combined with monochromators.

[0082] For reproductions with different wavelengths, particularly the first and second wavelength ranges, it is preferable to use illumination radiation within each of the different wavelength ranges, such as the red wavelength range (preferably 620 nm to 700 nm), the green wavelength range (preferably 500 nm to 560 nm), and / or the blue wavelength range (preferably 420 nm to 475 nm).

[0083] For example, for this purpose, a laser system with three monochromatic lasers or a multicolor laser with laser emission in the red, green, or blue (RGB) range can be provided.

[0084] In the context of this invention, "alignment of the master hologram" preferably means moving the master hologram from its current position to a target position. Preferably, the movement from the current position to the target position includes slight corrections, particularly to compensate for positioning errors, and is therefore different from the step of bringing the master stack or the master hologram to the workstation. Alignment preferably includes translation in the lateral direction, translation in the longitudinal direction, and / or rotation in a plane including the lateral and longitudinal directions. The lateral and longitudinal directions are preferably orthogonal to each other and / or parallel to the replica stack in the plane including the master hologram. Preferably, the movement for alignment is on the order of order of compensating for any errors in the positioning of the master hologram. For example, translation in the longitudinal and / or lateral directions can be up to 1000 micrometers, preferably up to 100 micrometers, particularly preferably up to 20 micrometers, and even more preferably up to 10 micrometers. Rotation is preferably up to 2°, preferably up to 1°, and particularly preferably up to 0.5°.

[0085] In the context of this invention, the "longitudinal direction" is preferably any direction in the plane formed by the surfaces of the respective master holograms. Preferably, this is a substantially horizontal plane. The longitudinal direction is particularly preferably aligned with the direction of movement of the replication stack to move into or out of the exposure station where exposure occurs.

[0086] In the context of this invention, the "lateral direction" preferably extends orthogonally to the longitudinal direction in a plane formed by the surfaces of the respective master holograms. The "rotation" of the master holograms preferably also occurs in this plane.

[0087] In the context of this invention, a "multicolor hologram" is preferably a hologram configured to diffract electromagnetic beams 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 multicolor hologram may include multiple channels, wherein each channel corresponds to a different wavelength and / or wavelength range. Each channel may be a copy of a master hologram configured for its respective wavelength or wavelength range. For example, channels may correspond to different colors, such as red, green, and blue light. In the context of this invention, a color preferably refers to light from a specific wavelength range of the visible spectrum (380 nm to 780 nm) having a bandwidth of less than 50 nm, preferably less than 40 nm, less than 30 nm, or even less, wherein the color has a maximum or peak value at its center wavelength characteristic. For example, for blue light, the center wavelength may be approximately 460 nm, while green light may exhibit a center wavelength of approximately 530 nm and red light a center wavelength of approximately 630 nm.

[0088] Preferably, one or more channels correspond to electromagnetic radiation outside the visible spectrum, such as UV or IR radiation. Different channels can exist in the multicolor hologram in the form of diffraction structures configured to diffract electromagnetic radiation of their respective wavelengths or wavelength ranges. The diffraction structures can exist in a single layer or in different layers of the photosensitive material.

[0089] In the context of this invention, the presence of multiple diffraction structures configured for different wavelength ranges within the same layer is referred to as "multiplexing." In a "multiplexed" hologram, the different diffraction structures are preferably overlapped in the material, wherein the different diffraction structures are assigned to different (color) channels or configured for different wavelength ranges. This means that in some embodiments, the master stack comprises multiple master holograms in different layers, but these master holograms may be replicated, wholly or partially, in the same photosensitive layer of a replica stack. A second photosensitive layer of the replica stack can be exposed using another master stack. Alternatively, however, the layer structure of the replica stack may mirror the layer structure of the master stack.

[0090] In the context of this invention, "photosensitive material" refers to a material that responds to radiation within the electromagnetic spectral range from an exposed master hologram. Preferably, the photosensitive material responds to light from the visible range of the electromagnetic spectrum. Particularly preferably, the photosensitive material responds to radiation by generating a localized change in its refractive index. This can occur, for example, through the localized polymerization of monomers or shorter polymer chains, as in photopolymers. The photosensitive material may lose its photosensitive properties during the process according to the method of the invention, for example, by fixation. For simplicity, the related material is still referred to as the photosensitive material in the replication stack even when it no longer responds to the incident light beam.

[0091] In a preferred embodiment of the present invention, the method includes the following further steps:

[0092] a. Apply the third photosensitive layer to the second photosensitive layer.

[0093] b. Provide a third master hologram configured for the third wavelength range.

[0094] c. Use light in the third wavelength range to expose the third master hologram to obtain the third replica hologram in the third photosensitive layer.

[0095] d. Fix the third replicated hologram in the third photosensitive layer.

[0096] In this case, multicolor holograms can be advantageously generated using a third replica hologram or a third (color) channel in a replica stack, without having to subsequently position the three exposed holograms vertically relative to each other. The resulting multicolor hologram can represent a sharp panchromatic image or another pattern from different ranges of the electromagnetic spectrum.

[0097] Known alternatives to generating holograms separately and stacking them on top of each other can lead not only to positioning errors between the first and second holograms, but also to further positioning errors between the third hologram and the stack of the first and second holograms. These combined errors can significantly degrade the quality of the resulting panchromatic image, even rendering the functional hologram unusable for its purpose. For example, if separate holograms exist for each wavelength range, it is difficult for a multicolor hologram acting as a light-collecting lens or reflector to have the same convergence point for all three wavelength ranges. By applying a third photosensitive layer to the second hologram before exposure, this source of error can be avoided, and the quality of the multicolor hologram can be improved. As mentioned above, the positioning of the additional unexposed photosensitive layer is less important than the positioning of the exposed hologram.

[0098] Applying a newly applied photosensitive layer to the exposure of the third master hologram also allows the third master hologram to be exposed with different parameters and / or in different materials than the first and second master holograms. For example, the third master hologram can be exposed with different wavelength ranges and / or different exposure angles. This enables the generation of multicolor holograms with complex functions.

[0099] Changing the exposure parameters allows for the exposure of different patterns and / or optical features in a multicolor hologram. For example, different photosensitive layers that are replicated and stacked can be exposed from different angles, wherein the angles differ from each other by at least 5°, preferably at least 10°. In this way, the reflective hologram can display different content depending on the viewing angle. For example, it might be preferable that the first content is visible from a left-hand viewpoint and the second content is visible from a right-hand viewpoint.

[0100] Even for multicolor holograms, where all channels should be visible from a single viewpoint, changing the exposure angle between exposure steps can be useful. The third master hologram may shrink or expand due to its production method. This can alter the wavelength characteristics of the master hologram. The angle at which the third master hologram is most effectively exposed may deviate from the target angle. By slightly adjusting the exposure angle from the target angle to the optimized angle, the third master hologram can be exposed with increased efficiency. This slight adjustment of the exposure angle is preferably less than 3°, and particularly less than 2°. Other holograms can continue to be exposed at the target angle or individually optimized angles.

[0101] By exposing each of the first, second, and third master holograms in a separate layer of the replication stack, each of the resulting holograms can exhibit properties different from those of the individual master holograms. For example, different master holograms can be exposed at different intensities. The relative position of the third hologram with respect to the first and / or second holograms can differ from the relative position of the third master hologram with respect to the first and / or second master holograms. Errors in the position of the second, third, or additional master holograms in the replication stack can also be corrected, as explained in more detail below.

[0102] In another preferred embodiment of the invention, the number of photosensitive layers or holographic layers in the multicolor hologram differs from the number of master holographic layers in the master stack or from the number of master holograms used in different master stacks. Specifically, the master stack may include two or more master holograms replicated in one, two, or more layers of the replication stack. Preferably, all master holograms of the master stack are replicated in the replication stack. A variation in the number of photosensitive layers can be provided for the exposure of two or more master holographic layers in the same photosensitive layer. This reduces the number of layers in the replication stack compared to the master stack. Alternatively or additionally, the variation in the number of photosensitive layers can be achieved by exposing the diffraction structure of a single-layer multiplexed hologram in two or more photosensitive layers, the diffraction structure being configured for different wavelength ranges. This increases the number of layers in the replication stack compared to the master stack. Using one or a combination of these techniques, the material structure and total thickness of the multicolor hologram may differ from the material structure and total thickness of the master stack. Depending on the application, this can help ensure, for example, the required total thickness and / or efficiency of replicated multicolor holograms, while minimizing positioning tolerances.

[0103] In a preferred embodiment of the invention, the master stack comprises multiple layers of wavelength-selective photosensitive material. Alternatively, the structure of the multicolor hologram can be optimized for its intended use. In applications (or further processing steps) where wear could lead to layer delamination or adhesive layer melting, it may be desirable to replicate multiple master holograms of the master stack, for example, in a single photosensitive layer. This reduces the risk of layers separating from each other. It also allows for a reduction in the overall thickness of the product because intermediate carrier or adhesive layers can be eliminated. The resulting multicolor hologram is particularly thin and robust, which facilitates its integration into the product.

[0104] In another preferred embodiment of the invention, two or more master holograms exist as multiplexed holograms. Preferably, the multiplexed hologram comprises a first master hologram and a second master hologram in the same layer. The first and second master holograms are specifically configured for different wavelength ranges and preferably do not overlap each other. The master holograms preferably comprise diffraction patterns present in the same material layer and diffracting radiation of different wavelength ranges. Such multiplexed holograms can be particularly compact and advantageously eliminate the lamination step for arranging the master holograms one on top of the other. However, compared to multicolor stacking, multiplexed holograms generally have limited efficiency in terms of the desired diffraction of the exposed radiation. However, advantageously, the multiplexed hologram can be converted into a multilayer multicolor hologram using the method according to the invention to improve efficiency. Thus, in step c, due to the configuration of the first master hologram for the first wavelength range, only the first master hologram of the multiplexed hologram can be replicated in the first photosensitive layer. Therefore, under appropriate, preferred monochromatic exposure, the first master hologram can be copied independently of other master holograms of the reused hologram.

[0105] In step f, the second master hologram can be replicated in the second photosensitive layer. This allows the first and second holograms to be replicated separately. The first and second holograms can also be replicated in different ways. For example, each of the first and second holograms can be replicated in a different type of photosensitive material. The photosensitive material can be particularly well-suited to capturing the characteristics of its respective hologram, especially for exposure within its respective wavelength range. This allows for improved quality of each individual hologram in a multicolor hologram compared to a multiplexed hologram.

[0106] Isolated replication of the master hologram enables higher efficiency in each replicated hologram. This can be achieved, in particular, through the specific selection of the photosensitive materials used, for example, by choosing a suitable photosensitizer for a specific wavelength range. This has the advantage of increasing the efficiency of the holograms in each photosensitive layer compared to the corresponding diffraction structure of the multiplexed hologram. The increase in efficiency can be 50%, 100%, 200%, or more (relative to the efficiency of the corresponding diffraction structure of the multiplexed hologram). For example, a multiplexed master stack with 30% diffraction efficiency for each RGB color channel can be advantageously used to obtain a replicated stack with a layered structure, where the replicated holograms in different layers exhibit 70% or higher efficiency.

[0107] In another preferred embodiment of the invention, the positions of each master hologram (or channel) within the multiplexed master hologram are adjusted prior to the exposure step. Therefore, lower positional tolerances can be achieved in multi-layer, multi-color holograms compared to those in multiplexed master holograms.

[0108] In a preferred embodiment of the invention, a subset of the master hologram in the multiplexed hologram is copied separately in a separate layer. It may be advantageous that another subset of the master hologram present in the same multiplexed hologram is not copied or is copied within a single photosensitive layer to form another multiplexed hologram in a copy stack.

[0109] In a further preferred embodiment of the invention, the master stack comprises a stack of multiple master holograms. A subset of these master holograms can be replicated in a single photosensitive layer of the replication stack to form a multiplexed hologram, while another subset of the master holograms can be replicated in the respective photosensitive layers of the replication stack. Therefore, techniques for combining master holograms into a multiplexed structure or dividing a multiplexed master hologram into separate layers can be combined as needed.

[0110] For example, it might be desirable to improve the efficiency of multicolor holograms generated from master stacks while ensuring a sufficiently low overall thickness for the application. In this example, the master stack comprises three or more master holograms. Specifically, the multiplexed holograms may include a first master hologram configured for red light, a second master hologram configured for green light, and a third master hologram configured for blue light. For example, the application might require particularly high efficiency for the third (blue) hologram to be replicated, which is not the case for the other color channels (red and green).

[0111] The first (red) and second (green) master holograms can be replicated as multiplexed holograms in a single photosensitive layer of the replication stack to maintain a low overall thickness. However, for improved efficiency, the third (blue) master hologram can be advantageously replicated separately in another dedicated photosensitive layer of the replication stack.

[0112] Therefore, the resulting multicolor holograms exhibit the high efficiency required for use in the respective color channels, while ensuring the desired low overall thickness. Thus, the method according to the invention allows for particularly flexible adaptation of the replication method to the desired characteristics of the replicated hologram for the application.

[0113] In another preferred embodiment of the invention, the method includes providing a third master hologram configured for a third wavelength range. The third master hologram can be copied into a second photosensitive layer to form a multiplexed hologram therein, preferably composed of the second and third holograms. Preferably, the second photosensitive layer is sensitive to light waves in both the second and third wavelength ranges. Step g of fixing the second photosensitive layer can then be performed to fix the second and third holograms therein. In this way, a master stack comprising three master holograms in three separate layers can be converted into a two-layer multicolor hologram. Alternatively, the third master hologram can also be copied into the first photosensitive layer, such that the first photosensitive layer comprises both the first and third holograms. The second photosensitive layer comprises the second hologram. The two-layer multicolor hologram allows for particularly low thickness in a product. This can be particularly useful if the multicolor hologram will be inconspicuously embedded, for example, between glass layers in a windshield.

[0114] In another preferred embodiment of the invention, the first and / or second master holograms are disposed in a master stack, wherein the same master stack or master stacks having the same configuration are used to expose the first and second photosensitive layers. Optionally, the first and second photosensitive layers may each be exposed using a master stack, wherein one master stack includes the first master hologram, and different master stacks include the second master hologram. By providing the first and second master holograms in the same master stack, the first and second holograms can be advantageously exposed in a single workstation. Movement of the replication stack between different exposure stations can be avoided, and the risk of longitudinal positioning errors of the replication stack can be eliminated. Therefore, both the first and second holograms can be exposed and fixed in one place before movement to form a stable layer structure. The risk of quality defects due to stray light or mechanical deformation of one of the layers is further reduced.

[0115] By providing the first and second master holograms in the same master stack, the master holograms maintain the same relative position to each other. Positioning errors may exist between the two master holograms. However, since these errors are constant, they can be advantageously compensated for in the same manner. This simplifies the implementation and control of the method for generating multicolor holograms with improved positional tolerances. By exposing the first and second photosensitive layers with the same master stack, the positional tolerances of the two holograms relative to each other can also be kept low. For a master stack with sufficiently low positional tolerances between the first and second master holograms, this can be achieved by exposing the same master stack without moving the master stack and / or the copy stack, resulting in equally low positional tolerances for the two holograms in the copy stack. Since the copy stack is not moved, no new positional errors are introduced, particularly in the longitudinal direction. To not only maintain low positional tolerances but also to improve them, the master stack can be moved between exposure steps to compensate for any positional errors in the second master hologram. This allows the second master hologram to be positioned on the first hologram with particularly high accuracy before the second exposure occurs.

[0116] This advantageously results in the replication stack exhibiting not only no additional tolerances due to the replication process, but even tighter positional tolerances than the master stack. Since compensation for positional errors typically involves only slight translations or rotations of the master stack (within fractions of a millimeter or up to 2°), it is particularly advantageous if the alignment process steps are performed directly after the exposure and fixation of the first hologram and before the replication stack is moved from the master stack. In particular, it is preferred that the replication stack maintains contact with the fixed surfaces of the master elements, especially with the substrate, while positional adjustment is performed. This is because adjustments can then be made with greater precision and without errors due to the flow or inaccurate slowing of the composite roll. The adjustment process is further explained below.

[0117] In order to expose the first and second photosensitive layers, in some embodiments, it is also preferable to use a master stack in each case, wherein the master stack exhibits the same or different configurations.

[0118] A first hologram can be exposed in a first exposure station and a second hologram in a second exposure station by exposing a first and a second photosensitive layer using two master plates stacked together. For this purpose, the replication stack can be advantageously configured to pass through the roll of material at each station. For example, the first hologram can be fixed in the first exposure station by activating a UV lamp or a thermal radiation unit. However, fixing can also be performed by a fixing module in a downstream workstation, which may include larger equipment for faster fixing of the first hologram. The space in the first exposure station does not need to be occupied by the fixing module, and the cycle time of the continuous replication method can be reduced.

[0119] Furthermore, this arrangement of the master holograms across different workstations can improve the speed and throughput of the replication method. In particular, in serial production, various method steps, such as exposure and fixation, can be advantageously performed simultaneously or in parallel with respect to different color channels in order to increase the yield of replicated multicolor holograms.

[0120] The application of a second photosensitive layer to a fixed first hologram can be performed in a separate workstation. This allows for the use of larger, dedicated equipment to apply the second photosensitive layer. The second photosensitive layer may, 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 chamber doctor blade. The second photosensitive layer may also alternatively comprise a solid layer laminated onto the first fixed hologram using one or more hot or cold lamination rollers. The second photosensitive layer may be self-supporting or include a carrier layer. Alternatively, the carrier layer can also be laminated onto the already applied photosensitive layer. This may require space unavailable in the first exposure station, and in some embodiments, this is best achieved by moving a replication stack through the workstation to apply the second photosensitive layer and / or additional intermediate layers. Furthermore, the replication stack can pass through an additional intermediate processing station between exposures.

[0121] In another preferred embodiment of the invention, the first hologram is exposed using a first master stack or master element. The second hologram is preferably exposed using a second master stack or second master element. Preferably, the first master stack or master element and the second master stack or master element are constructed differently. Therefore, the first master hologram can only exist in the first master stack, and the second master hologram can only exist in the second master stack. This reduces the layer structure of the master stack or master element. 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. This also applies to embodiments using three master holograms. The three master holograms can each be set in a separate stack or master element.

[0122] In particular, if only a single master hologram exists in each master stack, alignment errors can be avoided by pressing multiple master holographic layers onto a single substrate. Therefore, the master stack itself can be free of positioning errors. The master stack can be configured as a cylindrical substrate with master holograms on its surface, allowing exposure and fixation to occur sequentially, especially when the replication stack is supplied in roll form. However, precise positioning of the first hologram already exposed in the replication stack relative to the second master hologram in its own master stack can be challenging, particularly in the longitudinal direction. Therefore, this embodiment can be used for holograms that are approximately uniform in the longitudinal direction. A master stack with only one master hologram can be configured as a plate, and its position is adjusted when the replication stack contacts it. The positioning of the master stack can be adjusted to ensure that the multicolor holograms exhibit very low positioning tolerances. Using only a single master hologram per master stack can also improve exposure quality by reducing unwanted reflections at the interface. This is because such a master stack comprises fewer material layers, which can have slightly different refractive indices. Therefore, optical losses at the interface between layers can be eliminated or reduced.

[0123] The master substrate or its cover can provide a rigid surface onto which an optical liquid can be applied to improve optical contact with the replication stack without the risk of leaving residue on the master hologram. In this way, interference-free optical transition of the beam between the master and replication stacks can be ensured, with minimal reflection and / or aberrations at the interface. This unwanted reflection leads to optical loss that reduces the efficiency of the replication method.

[0124] In another preferred embodiment of the invention, exposure of the first and / or second master holograms occurs at the first and / or second exposure stations, respectively. Preferably, at each exposure station, the position of the respective master hologram is adjusted relative to the replication stack in the longitudinal and / or lateral directions. Preferably, the adjustment includes translation and / or rotation of the master hologram relative to the replication stack. This can be achieved by moving the entire master stack or a master element comprising the master hologram or a movable portion thereof. In this way, the advantages of individual exposure stations can be combined with the advantages of improved tolerances in the replication stack.

[0125] In another preferred embodiment of the invention, a replica stack including a first and / or second photosensitive layer is optically contacted with a second master hologram. For this purpose, the replica stack is preferably pressed onto a substrate, wherein the second master hologram is movably mounted relative to the substrate. An optical fluid is preferably present between the master hologram and the substrate. This allows for preferably smooth movement of the master hologram (or particularly a master stack including the master hologram) relative to the substrate. Preferably, the optical fluid has the same or similar refractive index as the surfaces of the substrate and / or the master stack. In the context of the invention, "similar refractive index" is preferably a refractive index that deviates from the refractive index of adjacent components by no more than 0.05, particularly no more than 0.03. This prevents undesirable reflections and losses at the interface between the substrate and the master stack. Preferably, the replica stack is laminated onto a substrate comprising a master element including the second master hologram.

[0126] In another preferred embodiment of the invention, a second master hologram is disposed in a master element. Optionally, the same master element also includes a first master hologram. Preferably, the second master hologram is present in or on a master substrate, wherein the master substrate is movably mounted relative to the base substrate of the master element. The replication stack is preferably temporarily laminated to the base substrate such that the carrier or protective layer of the replication stack is in contact with the base substrate. The substrate preferably comprises a rigid transparent plate. For example, a portion of a continuous composite roll can be temporarily laminated to the surface of the base substrate by rolling. Lamination can be performed using an optical adhesive film applied between the replication stack and the base substrate. This can stabilize the composite roll during the duration of the exposure and / or setting steps.

[0127] In another preferred embodiment of the invention, translation and / or rotation of the master substrate are performed to position the second master hologram on the replication stack 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 effective if the exposure steps are performed in the same workstation and the first and second master holograms are fixed to each other in the master stack. In this case, alignment can be performed in the same manner for each generated multicolor hologram, such that pre-stored master stack movement steps eliminate the need for conventional measurements of alignment errors.

[0128] Preferably, translation and / or rotation can be performed based on the detected position of the first hologram in the replica stack. The position of the first hologram can be detected, for example, by means of sensors and / or alignment marks. In this way, the second master hologram can be precisely aligned relative to the first hologram.

[0129] The use of a substrate allows for functional separation between the master stack and the substrate. The substrate preferably has a flat surface. The substrate can be specifically configured for optical contact with the replication stack. This allows the substrate to advantageously remain stationary during the various stages of exposure, while the master stack can be aligned for optimal replication, as described. Advantageously, in this way, no stress or deformation is introduced into the replication stack through translation and / or rotation. Friction between the master stack and the replication stack that can occur during alignment is avoided. Such friction can impair alignment, preventing it from proceeding to the desired extent. Instead, a stable mechanical contact exists between the substrate and the replication stack, while the relative movement for aligning the master hologram occurs within both master elements, particularly between the substrate and the master stack.

[0130] The substrate can preferably be mounted on a device that maintains its stability. This is to further improve the stability of the mechanical contact between the replication stack and the master components. By bringing the replication stack into contact with the substrate but not with the master stack, the master stack can be protected from friction, adhesive residues, etc. Therefore, the substrate can be cleaned more easily, especially by separating it from the master components and / or from the holding device on which it is mounted. The substrate can also be replaced more easily and cost-effectively.

[0131] Furthermore, the substrate allows for excellent optical contact between the replication stack and the master stack, which is spaced apart from the replication stack and remains freely movable. For this purpose, it is preferable that the substrate comprises the same material as the master stack (especially the master substrate). The substrate may additionally or alternatively comprise the same material as the adjacent layers of the replication stack.

[0132] The substrate is preferably configured such that an electromagnetic beam from the replication stack flows into the corresponding master hologram and returns to the replication stack. Preferably, the substrate is transparent to the wavelength of the electromagnetic radiation used to irradiate the replication stack at the corresponding workstation. Preferably, the refractive index of the substrate is approximately equal to the refractive index of an adjacent layer of the replication stack, which can be a carrier layer or the replication substrate itself. The refractive index of the substrate is preferably between 1.4 and 1.6. This allows for a very good optical contact between the replication stack and the substrate, eliminating light loss due to total internal reflection at the interface between the replication stack and the substrate. This unwanted reflection can constitute stray light, which can impair the quality of the reconstructed multicolor hologram. This is advantageously prevented in this case.

[0133] In a preferred embodiment of the invention, optical contact between the replication stack and the substrate is provided by an intermediate material. The material between the replication stack and the substrate can be a solid, such as a film, particularly an adhesive film, or a deformable transparent element, for example, made of silicone. The material can also be a semi-solid substance, such as a gel. Alternatively, the material can include a liquid, such as an optical liquid. In a preferred embodiment of the invention, optical contact between the substrate and the master stack is provided by an intermediate material. This material is preferably a liquid such that it does not impede movement of the master stack relative to the substrate.

[0134] Preferably, during exposure, an optical fluid is present between the master stack and the substrate. This optical fluid preferably has a refractive index corresponding to or close to the refractive index of the substrate, master stack, master hologram, and / or master hologram, and improves the optical contact between them. The optical fluid has the advantage of allowing frictionless movement of the two components while achieving interference-free optical contact. The optical fluid can also absorb any vibrations occurring during exposure, particularly those caused by movement of the master stack. This allows the replication stack to remain particularly stable during exposure.

[0135] In some embodiments, an optical adhesive film is provided to impart optical contact between the substrate and the replication stack (particularly the replication substrate). Preferably, direct mechanical contact is provided between the optical adhesive film and two adjacent substrates or between the substrate and the replication stack. If a gap exists between the surface of the optical adhesive film and adjacent substrates, it is preferably less than half the wavelength of the radiation used for exposure, such that no interference field is formed at the interface between the surfaces. Thus, the optical adhesive film can improve the optical contact between the replication stack and the master element. Particularly advantageously, it is not necessary to remove the optical adhesive film from the replication stack between the exposure of the first master hologram and the second master hologram. The optical adhesive film also helps stabilize the position of the replication stack relative to the master element. This makes the replication method particularly effective.

[0136] In another preferred embodiment of the invention, an optical liquid is introduced between the substrate and the replication stack to impart optical contact. The optical liquid can advantageously be applied continuously without a lamination step. On the one hand, this is faster and more efficient than applying an optical adhesive film. Simultaneously, the risk of leaving adhesive residue on the substrate can be avoided. Furthermore, the optical liquid can serve as a lubricant to protect the substrate from surface damage.

[0137] Providing a substrate between the replication stack and the master stack, particularly through the introduction of optical fluids and / or adhesive films at the interface, ensures exceptionally stable, vibration-free mechanical contact between them. This significantly reduces the risk of unwanted displacement during the exposure process. Furthermore, this arrangement provides efficient optical contact, thereby ensuring that the beam used for exposure remains substantially uninterrupted along the path between the master hologram and the photosensitive layer. The exposure process is therefore efficient and produces a clear holographic image.

[0138] For the purposes of this invention, the "optical adhesive film" is preferably a transparent film with a refractive index close to that of the master substrate, the replica substrate, and / or the photosensitive material. The optical adhesive film is preferably configured to improve optical contact between the substrate and the replica stack, thereby reducing or eliminating reflections at the interface between the substrate and the replica substrate.

[0139] Preferably, the material used for the optical adhesive film exhibits the same or similar optical properties as those of the materials used for the substrate or adjacent layers of the replication stack. Preferably, similar or identical properties include transparency, haze, stress birefringence, and / or refractive index. The use of the same or similar materials allows the refractive index of the optical adhesive film to be very closely matched to the refractive index of the adjacent substrate and / or replication substrate, ensuring a smooth transition between adjacent refractive indices without refractive index jumps. Therefore, reflections at the interface between the master element, the optical adhesive film, and / or the replication stack are largely eliminated or significantly minimized.

[0140] The "optical liquid" as defined in this invention is preferably a transparent liquid having similar or identical optical properties to a substrate, master mold substrate, master mold stack, replica substrate, and / or replica stack. Preferably, similar or identical properties include transparency, haze, stress birefringence, and / or refractive index. The use of optical liquids can prevent undesirable reflections at interfaces between components.

[0141] In another preferred embodiment of the invention, the substrate comprises optical glass and / or optical plastic. Preferably, the optical glass or optical plastic is selected from the group consisting of polymethyl methacrylate (PMMA), polycarbonate (PC), cyclic olefin polymers (COP) and cyclic olefin copolymers (COC) and / or optical glass, preferably selected from borosilicate glass, quartz glass, B270, N-BK7, N-SF2, P-SF68, P-SK57Q1, P-SK58A and P-BK7. Preferably, the substrate has a refractive index between 1.4 and 1.6.

[0142] In another preferred embodiment of the invention, a master stack can be used without a substrate. In this case, it is preferable to place the replica stack at a predetermined distance from the master stack during exposure. The predetermined distance is preferably large enough to prevent undesirable mechanical contact between the master stack and the replica stack. However, the predetermined distance is also preferably small enough that it can be bridged by an optical liquid that is kept stable by intermolecular forces. Preferably, an optical liquid is introduced between the master stack and the replica stack.

[0143] In another preferred embodiment of the invention, the first and / or second master holograms are disposed in a master stack including a master substrate. Preferably, the master substrate is located on the replication substrate of the replication stack. An optical fluid is preferably applied between the master substrate and the replication substrate. In such an embodiment, the replication substrate may be rigid and perform the function of a substrate. The replication substrate may support the optical contact between the master hologram and the replication substrate while providing a support surface for the lamination of additional layers. In the case of a rigid replication substrate, the optical adhesive film is preferably used only to bring the replication substrate into contact with another fixed portion, particularly with the substrate of the master element. The replication substrate may alternatively exist in the form of a film. If a film-like replication substrate is brought into contact with a movable master element, the optical contact between the movable master element and the replication substrate is preferably established by an optical fluid.

[0144] In a preferred embodiment, the substrate, master mold stack (especially the master mold substrate), and / or replica substrate may be provided with an anti-reflective coating. This coating can help to further reduce efficiency losses due to reflection.

[0145] In some embodiments, a rigid replication substrate can be used instead of a base substrate. In this way, the rigid replication substrate can be bonded to the remaining layers of the replication stack and used for further processing. In embodiments using a replication substrate instead of a base substrate, an optical liquid can be placed between the replication substrate and the master stack. This provides advantages similar to placing the optical liquid between the base substrate and the master stack. In such embodiments, the substrate for each multicolor hologram is preferably separate. The in-situ lamination of the optical adhesive film onto the substrate can be omitted, allowing for faster exposure. The optical adhesive film does not need to be removed after exposure. The need to clean the base substrate is also eliminated; instead, the multicolor hologram can be constructed directly on the replication substrate and exhibits very good quality.

[0146] In some applications, rigid replication substrates can form part of the final product, for example, as a carrier layer to incorporate multicolor holograms into the final product. This is particularly advantageous when multiple multicolor holograms are to be stacked one on top of the other with precise relative positions. Using rigid replication substrates for various multicolor holograms provides an alternative to roll-based stacking or lamination methods, which can result in distortion of the replication stack. The replication substrates may include positioning marks. These can be used, for example, to precisely position two multicolor holograms one on top of the other, such that the two multicolor holograms are encapsulated between two replication substrates, with the corresponding positioning marks aligned with each other.

[0147] In an embodiment of the invention, the exposed and preferably fixed multicolor hologram can be layered from a rigid replication substrate to obtain a flexible multicolor hologram. The rigid replication substrate can then be reused.

[0148] The replication substrate provides sufficient rigidity to the replication stack, allowing it to remain exceptionally stable during multi-step exposure. Furthermore, the strength and rigidity of the replication substrate enable the lamination of additional layers and / or the removal of layers from the replication stack between exposure steps without undesirable deformation. This allows for the application of additional photosensitive layers at a separate workstation, without the replication stack contacting the master element.

[0149] In another preferred embodiment of the invention, the replication substrate exists in the form of a film. This replication substrate can also carry multicolor holograms. Furthermore, the replication substrate may include positioning marks for stacking multiple multicolor holograms one on top of the other, such that the positioning marks can be subsequently cut off or the replication substrate can be removed from the final product. In such an embodiment, the replication substrate may preferably be provided in roll form, so that it can be laminated to a rigid surface of a substrate and easily transported to another workstation in a continuous process. In such an embodiment, the resulting multicolor holograms can advantageously be flexible, thereby facilitating their integration into three-dimensional components such as windshields.

[0150] In a preferred embodiment of the invention, the translation and / or rotation of the master hologram are controlled by a control unit. This allows translation and / or rotation to be performed with specific precision and repeatability.

[0151] The term "control unit" preferably refers to any computer unit having a processor, processor chip, microprocessor, or microcontroller capable of automatically controlling one or more actuators, such as sliders, motors, brakes, electromagnets, etc. The components of the control unit can be conventional or individually configured for their respective implementations. Preferably, the control unit includes a processor, memory, and computer code (software / firmware) for the components used to control the device.

[0152] The control unit may also include a programmable circuit board, microcontroller, or other device for receiving and processing data signals from components of the device, such as data signals from sensors relating to the speed of the composite roll and / or the position of the master hologram (particularly the position of alignment marks on the master hologram) and other related sensing information. The control unit preferably also includes 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 mounted. The computer code or software used to control the components of the device can be written in any programming language or model-based development environment, such as, but not limited to, C / C++, C#, Object-C, Java, Basic / Visual Basic, MATLAB, Python, Simulink, StateFlow, LabVIEW, or Assembler.

[0153] The term "control unit is configured to" perform specific work steps, such as translating and / or rotating master stacks, may include customer-specific or standard software mounted on the control unit that initiates and controls these work steps.

[0154] In another preferred embodiment of the invention, reference values ​​for the desired degree and / or direction of translation and / or rotation of the first and second master holograms are stored in a memory. Preferably, the control unit is configured to control the translation and / or rotation of the master stack (including the first and second master holograms) based on the reference values. In a preferred embodiment, the reference values ​​of the control unit are automatically and repeatedly provided for a series of replica stacks (or a series of portions of a continuously fed replica stack). By preloading the reference values ​​into memory, alignment of the master holograms can be performed for repetition of the same exposure step sequence without recalculating the required alignment. Complex steps of converging to the alignment position of the master holograms can be skipped. This allows for very fast and automatic processing of unexposed replica stacks or unexposed photosensitive layers.

[0155] In some preferred embodiments of the invention, instructions for aligning the first master hologram and the second master hologram are determined experimentally. For this purpose, the first and second holograms may be provided with alignment marks during their production. The alignment marks of the holograms can be compared with external alignment marks outside the master stack indicating the target position of the holograms. For example, the external alignment marks may exist on the replication stack or the substrate. Alternatively, the external alignment marks may exist only in the software, for example, as predetermined image coordinates.

[0156] Preferably, the desired alignment of the holograms can be determined by translating and / or rotating the stacked master holograms until the alignment marks in each of the first and second holograms spatially coincide with the external alignment marks representing the target position of the respective holograms. This can be accomplished by incrementally translating and / or rotating the respective holograms and evaluating the match between the respective alignment marks and the target alignment marks. The evaluation can be performed by software, particularly image analysis software. It is also preferable to store in memory the degree and / or direction of the translation and / or rotation of the holograms, for which the optimal alignment or optimal image quality has been evaluated. The selection of the translation and / or rotation positions to be verified can be repeatedly performed to converge to a position with optimal alignment. Preferably, the convergence function can be used to select the translation and / or rotation positions, i.e., preferably, based on a mathematical or algorithmic process of refining the estimates until they are sufficiently accurate or converge to an optimal value according to defined constraints. The convergence function used to select the optimal translation and / or rotation positions can be, for example, based on an iterative or recursive algorithm.

[0157] As an alternative to using alignment marks, the holographic image or optical function of each master hologram can be compared with the correctly aligned target function. This can be done by reconstructing the hologram, particularly the relevant wavelength channels, and evaluating the match between all or part of the reconstructed hologram and the target function. This can also be done using software, particularly image analysis software.

[0158] In another preferred embodiment of the invention, in order to determine the desired degree and direction of translation and / or rotation of the first and / or second master holograms, the master stack is illuminated with collimated reconstruction light to generate a convergence point (e.g., a focal point). This is particularly suitable for master holograms with the optical functions of concave mirrors or light-focusing lenses.

[0159] Preferably, the desired degree and / or direction of translation and / or rotation of the first and / or second master holograms is selected such that the convergence point of the reconstructed light in the first wavelength range coincides with the convergence point of the reconstructed light in the second wavelength range. An external target point can be used as a reference for the location of the convergence point. Alternatively, the actual convergence point of the light from the first or second master hologram can be used.

[0160] In this way, different wavelength channels can be exposed, allowing all channels of the multicolor hologram to be focused onto a single point on the planar wavefront. This allows multicolor holograms to achieve the optical functions of conventional optical elements in a more compact form, without chromatic aberration.

[0161] In other preferred embodiments of the invention, additional or alternative alignment methods may be used to determine the desired alignment of the individual master holograms in the master stack. For example, each master hologram may be provided with a positioning mark. The master stack may then be moved incrementally until the position of the positioning mark matches the target position. The positioning mark may take any form, such as an imprint, notch, or holographic element.

[0162] Preferably, the translation and / or rotation required to achieve optimal alignment of the master hologram are recorded as instructions in memory. Preferably, the control unit is configured to signal the actuator to translate and / or rotate the master hologram according to the previously recorded instructions.

[0163] To perform translation or rotation, providing an alignment module may be advantageous. This could include an entry structure in which the master stack is located. It may also be preferred that the master stack is positioned in or on a bracket that can be translated via two orthogonal axes, for example by means of pins, guides, etc. It may also be preferred that the bracket is located on a rotatable carrier connected to a motor (e.g., a piezoelectric motor). Of course, additional pins, gears, etc., can be provided for fine adjustment and / or restriction of movement.

[0164] In another preferred embodiment of the invention, a first master hologram and a second master hologram are arranged in or on a master substrate to form a first master stack, wherein the master substrate is preferably translated and / or rotated by an alignment module to perform alignment.

[0165] The master substrate is preferably configured as a layered structure carrying a first master hologram, a second master hologram, and optionally a third or additional master hologram. Preferably, the first and second master holograms are laminated onto the surface of the master substrate to form the layered structure. The master substrate is preferably rigid and transparent to both a first and a second wavelength range. The dimensions of the master substrate are preferably larger than the dimensions of the master holograms in all directions. Preferably, the thickness of the master substrate is at least 5 times, more 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 may preferably have the shape of a cuboid, plate, cylinder, or prism. At least one surface of the master substrate is preferably parallel to the master hologram and intersects the longitudinal and transverse directions.

[0166] The master substrate is preferably formed of a material that is an optical plastic, preferably selected from: polymethyl methacrylate (PMMA), polycarbonate (PC), cyclic olefin polymer (COP) and cyclic olefin copolymer (COC) and / or optical glass, preferably selected from: borosilicate glass, quartz glass, B270, N-BK7, N-SF2, P-SF68, P-SK57Q1, P-SK58A and P-BK7. Preferably, the master substrate has a refractive index between 1.4 and 1.6.

[0167] By attaching or integrating the first and second master holograms onto or into the master substrate, high robustness and protection against damage to the master stack can be ensured. Due to its larger size and higher rigidity, it can also be translated and rotated in a particularly reproducible manner without the risk of stretching, shrinking, or otherwise deforming. Furthermore, precise translation and / or rotation are facilitated.

[0168] Preferably, the photosensitive layers of the first replica stack are applied, exposed, and fixed in a sequence that is mirror-symmetric to the layer structure of the master hologram. This mirror symmetry particularly affects the photosensitive layers of the replica stack. In this way, the optical function of the generated multicolor hologram can precisely correspond to the optical function of the multilayer master hologram. When inverted, this multicolor hologram has the same layer structure as the master hologram. The arrangement of the layers can be specifically configured to minimize filtering effects between layers and improve the efficiency of the optical function of the multicolor hologram.

[0169] In another 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 range corresponds to green light, and yet another wavelength range of the first, second, or third wavelength range corresponds to blue light. For example, the first wavelength range corresponds to red light, the second wavelength range corresponds to green light, and the third wavelength range corresponds to blue light.

[0170] In another 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 nm and 750 nm, and particularly preferably between 620 nm and 700 nm. Preferably, one of the first, second, or third wavelength ranges corresponds to green light, wherein the wavelength range is preferably between 490 nm and 590 nm, and particularly preferably between 500 nm and 560 nm. Preferably, one of the first, second, or third wavelength ranges corresponds to blue light, wherein the wavelength range is preferably between 380 nm and 490 nm, and particularly preferably between 420 nm and 475 nm.

[0171] In this way, multicolor RGB (red-green-blue) holograms can be created. Such holograms can appear to redirect light from virtually the entire visible spectrum, thus generating high-resolution full-color holographic images. These images achieve very high visual quality due to the precise alignment of the channels. Multicolor RGB holograms can also redirect white light in a compact manner, which is particularly useful for HOEs integrated into cars, airplanes, or other vehicle windows.

[0172] In another preferred embodiment of the invention, the first, second, and third master holograms are reflection holograms. Reflection holograms can be reproduced particularly efficiently using the method according to the invention to generate sharp images. A particularly preferred embodiment of the reflection multicolor hologram is the so-called "Z-hologram," which can convert a spherical wavefront into a planar wavefront with a predetermined radiation angle. This will be referred to below. Figure 8 Further explanation.

[0173] In another preferred embodiment of the invention, the photosensitive layer comprises a photopolymer. The photopolymer is preferably sensitive to light in at least a first wavelength range and a second wavelength range. Using photopolymers in the photosensitive layer 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, the photopolymer can be provided in liquid form and applied to the replication stack to form the photosensitive layer. The thickness of each photopolymer layer can be adjusted by modifying the application mechanism. Such a photosensitive layer does not require an adhesive to stably adhere to the replication stack and can then be fixed immediately after exposure. This is particularly advantageous for forming thin, multilayered structures in the replication stack without using adhesives or carrier layers between the photosensitive layers. However, optionally, the photopolymer can be provided in liquid form between two transparent carrier films, which can be bonded to an existing replication stack using, for example, a suitable transparent adhesive.

[0174] Photopolymers can also be provided as resins or solids, for example, through a pretreatment that partially fixes the photopolymer, preferably before exposure. Resin or solid photopolymers can be applied to a single carrier layer, where the uncovered surfaces adhere to the replication stack without the use of adhesives. Optionally, the carrier layer can be removed after the resin or solid photopolymer has been applied to the replication stack, particularly after exposure and fixation of the photopolymer. Solid photopolymer layers can also be self-supporting. Therefore, photopolymers offer great flexibility in configuring the structure of replication stacks. In particular, they can allow the replication stack to expose holograms in different layers while maintaining a low overall thickness, as adhesive and carrier layers can be omitted in some cases.

[0175] In another preferred embodiment of the invention, the photosensitive layer is applied by adhesion. Applying the photosensitive layer by adhesion may be particularly preferred when the photosensitive layer is present between carrier layers. In a preferred embodiment, adhesion is performed by applying an optical adhesive film to the carrier layer of the replication stack and / or the photosensitive layer. The optical adhesive film may be specifically configured for permanent adhesion and exhibits the same or similar refractive index as the adjacent carrier layer or photosensitive material. The optical adhesive film can be applied to the replication stack by removing a protective layer and laminating. In another preferred embodiment, the adhesive is applied to the replication stack by spraying, brushing, or printing.

[0176] In another preferred embodiment of the invention, the photosensitive layer is applied by lamination. Preferably, lamination is performed by at least one lamination roller at 20–300°C, more preferably 40–200°C, particularly 60–80°C. Lamination can be configured to at least partially bond a carrier film on a replica stack to the carrier film of the photosensitive layer. Preferably, the lamination temperature is selected based on the materials of the two carrier films, such that one or both carrier films reach their melting point within a short time. The preferred temperature also depends on the photopolymer formulation and should not impair the photosensitivity of the photopolymer.

[0177] Lamination is preferably performed at a pressure of 10 to 20,000 N. The required pressure preferably depends on the width of the photosensitive layer, the thickness of the target layer, and / or the lamination speed. The application of preferred pressure can particularly increase the adhesion of the photosensitive layer (especially a solid photosensitive layer) to the replication stack. Any air gaps between the photosensitive layer and the replication stack can be eliminated, preventing unwanted reflections at the interface. This allows for excellent optical contact between the replication stack and the newly added photosensitive layer. In some embodiments, lamination is combined with the application of an adhesive layer to achieve a seamless bond between the layers of the replication stack.

[0178] Preferably, the photosensitive layer is laminated onto the replication stack directly onto the substrate in the exposure station. The substrate is preferably held in place during exposure and lamination. Preferably, the substrate is a replication substrate or a base substrate. This means that lamination can be performed in the same location as the exposure, without needing to move the replication stack to a separate lamination station. Since moving the replication stack can cause positioning errors, especially in the longitudinal direction, this can be avoided by performing the lamination step in situ. Using a solid substrate, particularly one with a flat surface, allows for the application of high pressure when a new photosensitive layer is applied. This allows the new photosensitive layer to have a predetermined thickness and adhere well to the underlying layer.

[0179] In another preferred embodiment of the invention, the application of the photosensitive layer includes coating a photopolymer in liquid form and optionally drying it. The photopolymer coating can be performed directly on the replication stack or on a carrier layer, which is then applied to the replication stack. Coating a liquid photopolymer to form the photosensitive layer can reduce the thickness of multilayer multicolor holograms because the liquid photopolymer adheres particularly well to the replication stack without the use of an intermediate layer. This allows for the omission of additional carrier or adhesive layers, simplifying the method.

[0180] Preferably, the photopolymer is coated using a coating module. In another 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 method. The coating module may include one or more coating elements, wherein suitable coating elements may be selected based on the layer thickness and rheological properties of the photopolymer. For example, the following may be preferred as coating elements: anilox rollers, screen cutters, profile rods, slot dies, squeegees, chamber squeegees, comma strips, and / or devices for squeegee methods.

[0181] In another preferred embodiment of the invention, the coating module is configured to coat a liquid photopolymer onto the surface of the replica stack. Preferably, the liquid photopolymer is applied by printing, roller coating, brushing, or spraying. Such a method allows the liquid photopolymer to be applied only to a portion of the surface of the replica stack. This allows for the formation of further patterns in the multicolor hologram.

[0182] The thickness of the photopolymer layer is preferably 1 to 200 μm. For photopolymer layers with a thickness between 1 and 15 μm, an anilox roller is preferably used in a gravure printing process. For photopolymer layers with a thickness between 7 μm and 40 μm, wire or profile rods are preferred. If the layer thickness is between 40 μm and 100 μm, a slit die, squeegee, or comma bar is preferred.

[0183] In another preferred embodiment of the invention, the method includes using 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 includes corresponding coating steps. By coating the two films separately and bonding them together, a thinner coating can be combined to form a thicker photopolymer layer. Preferably, the combination step is performed by laminating the two coated carrier films to encapsulate the photopolymer layer between them. An advantage is that the thinner layer is degassed more quickly. The solvent in the coating can evaporate more quickly before the lamination process.

[0184] Furthermore, coating with an additional carrier film enables the production of photopolymer stacks. For example, a stack of two or more liquid photopolymer layers, each separated by a carrier film, can specifically comprise two different photopolymer compositions, where each composition is sensitive to light within a specific wavelength range. For example, a second hologram, a third hologram, or additional holograms can be exposed in different photopolymer layers without applying a new photosensitive layer to the replica stack between these exposure steps. This can be particularly effective if the second, third, or additional holograms can be exposed at the same workstation and do not need to be combined with each other, for example, as multiplexed holograms in a single layer. This can also be effective where the photopolymer layers of the photopolymer stack are wavelength-selective and / or the corresponding master holograms do not need to be aligned. These photopolymer layers can then be exposed in a single workstation. Subsequently, all photopolymer layers of the photopolymer stack can be fixed.

[0185] In another preferred embodiment of the invention, the replication substrate, photosensitive layer, and / or replication stack are present in rolls of any length. The replication substrate may be in the form of a transparent film, which is preferably provided in rolls. The photosensitive layers may each be supplied with at least one carrier film, which is optionally removed after the photosensitive layer is applied to the replication stack. In this way, the photosensitive layer is transferred to the replication stack through an intermediate layer without excessively increasing the thickness of the replication stack. Preferably, the photosensitive layer is also provided in rolls. The replication stack may also be provided in rolls and further constructed in this process. Preferably, the replication stack can be rolled up again after replication.

[0186] Setting the replica substrate, photosensitive layer, and / or replica stack as a roll of any length allows the use of rollers to transport the respective rolls through different workstations. This arrangement is particularly suitable for continuous methods, enabling short cycle times and high throughput. Furthermore, the movement of the roll can be restricted, making rotation and / or lateral displacement preferably impossible or severely limited. For example, the dimensions of the conveyor rollers can be adjusted to closely approximate the width of the roll, thereby preventing unwanted movement of the roll in the lateral direction.

[0187] In another preferred embodiment of the invention, the replica substrate, photosensitive layer, and / or replica stack are conveyed on a traveling roll by conveyor rollers. In this case, the replication process is preferably performed continuously. If the replica substrate is constructed as a solid three-dimensional body, the use of a moving roll may be particularly advantageous. Since such a replica substrate cannot be rolled up, it is advantageous to handle the replica substrate in a continuous process using conveyor rollers. The conveyor rollers also prevent undesirable movement of the replica substrate, photosensitive layer, or replica stack in the lateral direction, particularly by adapting the width of the conveyor rollers to the width of the replica substrate. This also limits unwanted rotational movement.

[0188] In another preferred embodiment of the invention, steps a. to k. are similarly repeated to copy the multicolor hologram into the second replication stack using the fourth, fifth, and sixth master holograms. The first and second replication stacks can be combined with each other to perform more complex optical functions.

[0189] For example, the two replica stacks may include a reflective hologram, wherein an incident beam is reflected by the first replica stack such that the beam falls onto and is redirected by the second replica stack. Preferably, one of the first and second replica stacks is exposed using a plane wavefront. Preferably, the other of the first and second replica stacks is exposed using a spherical wavefront. In this way, one of the two multicolor holograms can be configured to convert a spherical wavefront into a plane wavefront, and the other of the two multicolor holograms can be configured to reflect a plane wavefront at a predetermined angle.

[0190] Multicolor holograms can perform the functions of convex or plane mirrors (along with convex lenses) in a very compact manner without undesirable chromatic aberration. Because multicolor holograms can be made from photosensitive materials with thicknesses in the micrometer range, they can perform their respective optical functions efficiently across multiple wavelengths while occupying very little space. Therefore, they can be discreetly integrated into AR glasses, car windows, aircraft windows, pilot training equipment, and more.

[0191] In another preferred embodiment of the invention, the first and second replica stacks or the first and second multicolor holograms are connected to each other, wherein the first and second multicolor holograms are preferably arranged at a distance of less than 1 mm, more preferably less than 0.5 mm, and particularly preferably less than 0.1 mm. Preferably, the first and second multicolor holograms have a layered structure, wherein the first layer corresponds to a first wavelength range and the second layer corresponds to a second wavelength range. Preferably, the multicolor holograms are arranged such that their layers are mirror-symmetrical to each other, that is, the order of the layers corresponding to each wavelength range is preferably the same from the center line outwards.

[0192] In this way, light-redirecting HOEs with very tight tolerances can be generated, resulting in very high efficiency. Since only two multicolor holograms can be applied and combined with each other in a known manner (e.g., by lamination), only alignment of the two generated multicolor holograms on top of each other is required. This represents a significant improvement over existing techniques, where six layers must be aligned and laminated one on top of the other to generate such multi-layered RGB holograms. The accuracy of the HOE can be significantly improved. The resulting multicolor HOE can combine the functions of convex and plane mirrors to perform complex electromagnetic beam redirection in a very compact manner.

[0193] In another aspect, the present invention relates to a replication stack comprising at least a first replicated hologram and a second replicated hologram, wherein the replication stack can be produced by a method according to the invention or a preferred embodiment thereof.

[0194] The first and second replicated holograms may preferably be present in one or more layers of fixed photosensitive material to provide a multicolor hologram. The first hologram is preferably exposed at wavelengths from a first wavelength range, while the second hologram is preferably exposed at different wavelengths from a second wavelength range, such that the resulting replicated stack can diffract radiation of two wavelengths. Additionally, the replicated stack may include further layers, such as a carrier film, a protective layer, and / or a replicated substrate.

[0195] This replication stack advantageously includes diffraction structures configured to diffract radiation with two or more different wavelengths. The diffraction structures corresponding to different wavelengths are advantageously precisely aligned with each other, enabling the replication stack to perform its optical function with high quality and very high efficiency. Undesirable light filtering caused by incorrect alignment of different wavelength channels is avoided.

[0196] Those skilled in the art will recognize that the technical features, definitions, and advantages of the preferred embodiments of the method according to the invention also apply to the replication stacking according to the invention, and vice versa.

[0197] Detailed description

[0198] The invention will now be explained in more detail with reference to examples and descriptions, but is not limited thereto. Attached Figure Description

[0199] Figure 1 This is a schematic diagram of a master stack structure that includes three master holograms in different layers.

[0200] Figure 2 This is a schematic diagram of the incremental construction of a multicolor hologram in a workstation using master stacking.

[0201] Figure 3A It is a schematic diagram of the alignment of the first master hologram, so that its focal point coincides with the reference point.

[0202] Figure 3B This is a schematic diagram of exposing the first master hologram onto the first photosensitive layer of the replication stack.

[0203] Figure 4A It is a schematic diagram showing the alignment of the second master hologram with the first master hologram and / or the first replica hologram, where the focal points coincide.

[0204] Figure 4B This is a schematic diagram of exposing the second master hologram onto the second photosensitive layer of the replication stack.

[0205] Figure 5A It is a schematic diagram showing the alignment of the third master hologram with the first master hologram, the second master hologram, and / or the first or second replica hologram, where the focal points coincide.

[0206] Figure 5B This is a schematic diagram of exposing the third master hologram onto the third photosensitive layer of the replicated stack.

[0207] Figure 6 This is a schematic diagram of the incremental construction of multicolor holograms using a single master stack.

[0208] Figure 7 It is a schematic diagram of a multicolor holographic optical element (particularly a “z-hologram”) comprising six holograms in a layered structure, which can be produced by the method according to the invention.

[0209] Figure 8 It shows Figure 7 Holographic optical elements and their light redirection function. Detailed Implementation

[0210] Figure 1 The diagram schematically illustrates the structure of a master stack 2 with three master holograms corresponding to three wavelength channels (specifically, RGB channels). The diagram shows the master stack 2 in plan view at various stages of its production. The master stack 2 includes a master substrate 10, which may be, for example, a glass plate. A first master hologram 4 is laminated onto the surface of the master substrate 10. The first hologram 4 is configured for a first wavelength range λ1, for example, the blue range of the visible spectrum. The length and width of the master substrate 10 are greater than the length and width of the first master hologram 4. This allows for… Figure 1 As seen in the first illustration.

[0211] Second Master Holographic Figure 6 It is laminated onto a stack including the master substrate 10 and the first master hologram 4. Second master hologram Figure 6 Configured for the second wavelength range λ2, specifically the green range of the visible spectrum. For example... Figure 1 As shown in the second illustration, during lamination, the second master hologram... Figure 6 There may be a positional shift between the second master hologram and the first master hologram 4. This means that the second master hologram... Figure 6 The longitudinal, lateral, and / or rotational positions of the first master hologram 4 may not perfectly correspond to the longitudinal, lateral, and / or rotational positions of the second master hologram 4. Furthermore, the first master hologram 4 and the second master hologram... Figure 6 The positions may not precisely correspond to their target positions on the master substrate 10.

[0212] Then the third master hologram Figure 8 Lamination onto the second master holographic plate Figure 6 This forms part of the layer structure of the resulting master stack 2. Third Master Holographic Figure 8 This corresponds to the third wavelength range λ3, such as the red range of the visible spectrum. Here, lamination also causes a shift, making the third master holographic. Figure 8 The position of the first master hologram 4 or the second master hologram Figure 6 The positions are not perfectly matched. Optionally, the master stack 2 may be provided with a transparent cover (not shown) to protect the master holograms. In the example embodiment, the three master holograms 4, 6 and 8 are reflective holograms and have optical functions for focusing incident radiation.

[0213] The quality of the hologram reconstructed from or generated by the master stack 2 or its optical functions may be limited due to the offset between the channels. The color channels of the master stack 2 are not perfectly matched, causing areas of the master stack 2 to appear with incorrect hues. However, using the method according to the invention, a multicolor hologram 20 with extremely low tolerances can still be generated using a master stack 2 with high tolerances.

[0214] The master stack 2 is preferably arranged on the substrate 42 and is provided with an alignment module to form the master element 12. The alignment module can change the translational or rotational position of the master stack 2 relative to the substrate 42. The substrate 42 preferably comprises a transparent rigid plate.

[0215] Figure 2 A method for generating a multicolor hologram according to another embodiment is shown. Incremental construction is preferably performed in a single workstation using the same master stack. A replication substrate 43 is provided. Figure 2 (Top left of the image). A first photosensitive layer 14 is applied to a replication substrate 43 by lamination to form a replication stack 44. The replication stack 44 is fed to an exposure station. A light source 48 generates a coherent light beam in a first wavelength range. The light beam is reflected by a first master hologram 4 in the master stack 2. The coherent light beam in the first wavelength range is used to expose the first master hologram 4 to generate a first hologram in the first photosensitive layer 14. After the first photosensitive layer 14 is exposed, the replication stack 44 is cured (…). Figure 2 (Top right of the image). Here, a UV lamp 50 and heat and / or white light can be used to fix the first hologram. In this step, the UV lamp 50 and other devices for curing can be simply activated and / or scanned to replicate the stack.

[0216] The second photosensitive layer 16 is applied to the replica stack 44 without moving the replica stack. The second photosensitive layer 16 can be applied directly to the first photosensitive layer 14 or an intermediate layer. The second photosensitive layer 16 is sensitive to a second wavelength range. In the same exposure station with the same master stack 2, for the second master hologram... Figure 6Exposure is performed to irradiate the second wavelength range from radiation source 48. Master stack 2 includes a second master hologram. Figure 6 Before its public release, the second master holographic... Figure 6 Preferably, the master stack 2 is aligned to adjust its positioning on the first exposed hologram. For this purpose, the master stack 2 is preferably translated and / or rotated. The magnitude and direction of the translation and / or rotation are preferably determined by detecting the existing position of the first hologram. This is performed, for example, by reconstructing the first hologram and / or detecting position markers. Therefore, the second master hologram... Figure 6 It can be precisely positioned relative to the first hologram to generate a multicolor hologram with very tight tolerances. The second master hologram is replicated in the second photosensitive layer 16. Figure 6 The light redirection function is then used. The second photosensitive layer 16 is then fixed in the same workstation.

[0217] Then, the third photosensitive layer 18 is applied to the replication stack 44 in the same workstation without moving the replication stack 44. The third photosensitive layer 18 is configured for a third wavelength range. Radiation in the third wavelength range is used to holographically represent the third master image. Figure 8 Copy it to the third photosensitive layer 18. In the third master holographic... Figure 8 Before being exposed, it is preferably aligned to adjust its position relative to the exposed first hologram and / or the exposed second hologram. The third master hologram is then replicated in a precisely aligned manner in the third photosensitive layer 18. Figure 8 The light redirection function is then applied. A third hologram is then fixed. The result is a multicolor hologram 20 with three holograms in different layers, where the hologram exhibits improved positional accuracy compared to the laminated hologram structure and also compared to the master stack 2.

[0218] In an alternative embodiment of the invention, the above steps can be performed in different workstations. For example, a replication substrate can be supplied to three different exposure stations to replicate first, second, and third master holograms. Each exposure station is preferably equipped with a different master stack 2. The first master stack 2 preferably carries the first master hologram 4, and the second master stack preferably carries the second master hologram. Figure 6 Furthermore, the third master stack preferably carries the third master hologram. Figure 8 The station for applying a new photosensitive layer (e.g., by lamination or coating) and the stationary station are preferably inserted between successive exposure stations.

[0219] Figure 3A and Figure 3B The illustration shows the source Figure 1The first master hologram 4 of the master stack 2 is copied into the photosensitive layer 14 of the replication stack 44. The master stack 2 is part of the master element 12, which also includes a substrate 42 movable relative to the master stack 2. In the first exposure step, the replication stack 44 includes the first photosensitive layer 14 and protective layers above and below it. The layer structure of the replication stack 44 is incrementally constructed by applying additional photosensitive layers. The advantage here is that the photosensitive layers do not have to be wavelength selective. The master holograms 4, 6, and 8 are preferably exposed in a mirror sequence in the replication stack 44. Since the first master hologram 4, corresponding to blue light, is closest to the first photosensitive layer 14 of the replication stack 44 in this case, the first exposure step is performed with blue light, particularly with a blue laser.

[0220] The upper side of the substrate 42 and the lower side of the master substrate 10 are arranged at a predetermined distance from each other, and each is provided with an anti-reflection layer to prevent unwanted reflections on the aforementioned sides. An optical liquid 30 is introduced between the upper side of the substrate 42 and the lower side of the master substrate 10, allowing light beams to traverse the distance between the substrate 42 and the master substrate 10 substantially without diffraction. To further prevent unwanted reflections at the interface between the replication stack 44 and the substrate 42, in... Figures 3A to 5B An optical adhesive film is inserted between these components during the duration of the steps shown. This optical adhesive film is not shown in the figure.

[0221] Prior to exposure, the first master hologram 4 is initially arranged such that it is in a target position relative to the replica stack 44. This is achieved by translating and / or rotating the master stack 2, which includes the first master hologram 4, as follows: Figure 3A This is schematically shown. During this process, the substrate 42 remains stationary. The position of the substrate 42 is shown by dashed lines. As shown below for... Figure 4A and Figure 5A As explained, this position remains unchanged during the three exposure steps. Translation and rotation of the master stack 2 are preferably performed by the alignment module according to previously stored instructions. The target position can be the location where the blue light used to reconstruct the first master hologram 4 converges to a convergence point 40 corresponding to predetermined coordinates. The position of the convergence point 40 can be pre-stored and compared with data from a photodetector monitoring the reconstruction of the first master hologram 4 to determine the alignment instructions.

[0222] The position of the master hologram 4 can also be adjusted relative to the position of the underlying substrate 42. For example, as Figure 3A As illustrated, the master hologram 4 can be centered directly above the substrate 42 with a predetermined margin.

[0223] To replicate the first master hologram 4, a plane wavefront comprising a reference beam 26, including blue light, is incident on the first master hologram 4. This process... Figure 3B The reference beam 26 is schematically shown in the diagram. It passes through the first photosensitive layer and is reflected by the first master hologram 4. The reflected object beam 28 interferes with the reference beam 26 in the first photosensitive layer 14, thereby forming an interference pattern therein. A first hologram 140 (shown in subsequent figures) is generated in the photosensitive layer of the replication stack 44. The first hologram 140 can be reconstructed using blue light (or light that includes the blue range of the spectrum) and performs the optical function of converting a spherical wavefront into a planar wavefront. The first hologram 140 (not shown) is fixed before performing further exposure steps. This can be done by activating a fixing module in the same workstation.

[0224] Figure 4A and Figure 4B The step of replicating the second hologram corresponding to the green channel is illustrated schematically. The positions of the replica stack 44 and substrate 42 are preferably kept unchanged. Figure 4A As shown, the second master holographic Figure 6 It can be translated or rotated to position it in the target location. Furthermore, a second photosensitive layer 16 can be applied to the replication stack 44 to further construct its layer structure. The second photosensitive layer 16 can be applied, for example, by lamination from a roller. To perform this lamination, the substrate 42 is preferably sufficiently rigid and stably fixed. The reference beam 26 of green light can then be guided to the second master hologram. Figure 6 The exposure is then performed. A green laser can be used for this purpose. Reference beam 26 is holographically mapped onto the second master plate. Figure 6 The beams reflect and converge at convergence point 40 to form an object beam 28. The absolute position of convergence point 40 is the same as the absolute position of the first master hologram 4. The reference beam 26 and the object beam 28 interfere in the photosensitive material 16 of the replication stack to form a second hologram 160. This is fixed before further exposure.

[0225] Similarly, the third master holographic Figure 8 It can be aligned according to predetermined instructions to bring it to the target location, such as Figure 5A As shown. A third photosensitive layer 18 can be added to the layer structure of the replication stack 44. A reference beam 26 can be guided to the third master hologram using a red laser. Figure 8 Furthermore, a third hologram 180 is generated in the replication stack 44. The third hologram 180 is also fixed before further processing. Therefore, the replication stack 44 comprises a multicolor RGB hologram. In this way, all three color channels of the multicolor hologram are precisely aligned with each other, as shown at the same position of the convergence point 40 in each exposure step. This is possible despite the alignment errors that exist in the master stack 2 using the method according to the invention.

[0226] The exposed and fixed multicolor holograms can be layered from the rigid substrate 42 to obtain flexible multicolor holograms, or the substrate 42 can be used as a rigid replication substrate to obtain stable multicolor holograms. The rigid replication substrate can be used to position multiple multicolor holograms vertically relative to each other in order to encapsulate the replicated holograms, preferably encapsulated between two rigid replication substrates.

[0227] Figure 6 It shows the use of from Figure 1 A method for producing multicolor holograms by stacking multiple master layers. Figure 6 In one implementation, the same master stack can be used to expose all three photosensitive layers of the first multicolor hologram 20. This can be done at a single workstation without having to move the copy stack 44 between exposure steps. Figure 6 The replication stack 44 includes a rigid replication substrate 43 and a first photosensitive layer 14. The replication stack 44 is preferably positioned on the surface of the master stack 2 such that the master stack 2 can be at least slightly movable relative to the replication stack 44. An optical liquid 30 is introduced between the surface of the master substrate 10 and the replication substrate 43 to create optical contact between these processing components. Additionally, an anti-reflective coating is provided on adjacent surfaces of the replication substrate 43 and the master substrate 10. To replicate the first master hologram 4 into the first photosensitive layer 14, the master stack 2 or replication stack 44 is positioned such that the first master hologram 4 is directly above / directly below the target position of the first hologram in the photosensitive layer 14. The first master hologram 4 is then exposed. In this embodiment, since the first master hologram 4 reflects blue light, the material of the photosensitive layer 14 is selected such that it is (at least) sensitive to blue light. Since the master hologram 4 performs a light-collecting function, the same light-collecting function is etched into the first photosensitive layer 14. This is accomplished by guiding one or more blue laser beams through photosensitive layer 14 onto the first master hologram 4. The blue laser beams are reflected by the first master hologram 4 toward the light collection point (focal point). The reflected beam (object beam) interferes with the incident reference beam in photosensitive layer 14 and forms a diffraction pattern. The diffraction pattern performs the same optical function as the first master hologram 4 and is considered a reflective hologram. In particular, the diffraction pattern can convert a planar blue wavefront into a converging blue wavefront. After exposure, photosensitive layer 14 is cured (“bleached”) by UV radiation and heat, so that the diffraction pattern is unaffected by further radiation. This causes photosensitive layer 14 to lose its photosensitivity. Curing can be performed in the same workstation as exposure, for example by activating a UV lamp and / or a heat source.

[0228] After the first hologram in the first photosensitive layer 14 has solidified, the second photosensitive layer 16 is applied to the replication substrate. Since the same master stack 2 is also used to expose the second photosensitive layer 16, the application of the second photosensitive layer can preferably be performed without moving the replication substrate 43. The second photosensitive layer 16 can be applied to the replication substrate 43 by spraying, printing, gluing, or other methods. The printhead can be activated to perform this step in the same workstation. Alternatively, a supply roller can provide a solid layer of photosensitive material, which is laminated onto the replication stack 43 using a laminating roller. Lamination is preferably used to seamlessly adhere the photosensitive material to the replication stack 43 without requiring an adhesive layer. The laminating roller can roll on the replication stack 43 before leaving the area where exposure occurs. In this way, it does not interfere with the exposure beam.

[0229] The second photosensitive layer 16 is preferably a second master holographic image. Figure 6 Exposure. This is in Figure 6 It is schematically shown in the upper right quadrant. Second master hologram. Figure 6 It can be configured to be in a predetermined alignment, specifically directly above the first master hologram 4. However, for example, due to the production process of the master stack 2, there may be a small deviation from the designated alignment. To compensate for the deviation from the designated alignment in the master stack 2, the master stack 2 can be slightly repositioned before exposure. The repositioning is preferably configured in such a way that the second master hologram... Figure 6 The holograms in layer 14 are precisely aligned above the first hologram according to the specified alignment conditions. In this way, the alignment of the holograms in the replica stack 44 can exhibit tighter tolerances than the alignment of the master holograms one above the other in the master stack 2.

[0230] In this implementation scheme, the second master hologram Figure 6 It is configured to reflect green light. Since the first hologram and the first master hologram 4 in layer 14 only reflect blue light, they have no effect on green light. Therefore, when using a green laser to expose the second master hologram... Figure 6 Initially, it could pass through these layers without being redirected. Then it was holographically mapped from the master plate. Figure 6 Reflection. The incident reference beam interferes with the reflective object beam in the photosensitive layer 16, which is sensitive to green light. A second hologram is formed in this layer 16 and then cured.

[0231] Then, the third photosensitive layer 18 is applied to the second photosensitive layer 16. The third photosensitive layer 18 is sensitive to red light and can be holographically reproduced using a third master template. Figure 8 Exposure is used to form a third reflection hologram with light-collecting capabilities. The third photosensitive layer 18 uses a third master hologram. Figure 8 Expose, then cure, such as Figure 6The lower right quadrant is schematically shown. The result is that the first multicolor hologram 20 comprises multiple layers, including a replica 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 in Figure 6 It is shown in the lower left quadrant. The multicolor hologram 20 can preferably collect white light at a single point, so that it can be used in a very compact manner as a combination of a convex mirror and a plane mirror.

[0232] As mentioned above Figure 2 The explanation is as follows: Figure 6 Multicolor holograms can also be generated similarly in different exposure stations with three master stacks. For example, the first master stack can be configured for blue light, the second master stack for green light, and the third master stack for red light.

[0233] Figure 7 The structure of a holographic optical element consisting of six reflective holograms is schematically shown, which can be generated by the method according to the invention. A first multicolor 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 multicolor hologram 20 is generated specifically by means of a master stack 2, which includes three reflective master holograms 4, 6, and 8. The master holograms reflect blue, green, and red light, respectively, which are the optical functions of the convex mirrors. Although the master holograms can exist in a single layer, in this embodiment, they each exist in a layer of the master stack 2. In this embodiment, the multicolor hologram 20 has the same number of holographic layers as the master stack 2. However, according to the invention, more than one master hologram can be replicated in the same photosensitive layer of the replication stack 44, such that the multicolor layer 20 can, for example, present only two holographic layers.

[0234] In the parallel approach, a second master hologram with different functions is used. Figure 2 A second multicolor hologram 22 with different light redirection functions is generated. In this embodiment, the second multicolor hologram 22 is a reflection hologram that reflects white light at a predetermined angle. Therefore, the second multicolor hologram 22 functions as a plane mirror.

[0235] Each of the first multicolor hologram 20 and the second multicolor hologram 22 presents a non-holographic underlayer, specifically the replica substrate 43. The two multicolor holograms 20 and 22 are arranged one above the other, as shown below. Figure 7As shown in the lower right of the image. A replica substrate 43 is used to align the multicolor holograms, such that they are encapsulated between two external replica substrates 43. This ensures no rotational position error occurs between the two holograms 20, 22. Since the diffraction pattern of the second hologram 22 is substantially consistent in both the longitudinal and transverse directions, translational displacement is less critical. The two multicolor holograms 20, 22 are bonded together, for example, by an optical adhesive layer and / or by lamination, to generate a holographic optical element. The holographic optical element has six holographic layers, where the tolerances and properties of the HOE are improved compared to the master stack 2 used.

[0236] Figure 8 A HOE comprising a first multicolor hologram 20 and a second multicolor hologram 22 is shown, each of which is generated using a method according to the invention. Each of the two multicolor holograms is an RGB hologram, wherein the RGB holograms are attached to each other in a mirror sequence. Therefore, the HOE (specifically, the "z-hologram") has, for example, a BGRRGB layer structure. While the first multicolor hologram 20 is as follows... Figures 3A to 5B The second multicolor hologram 22 is generated as shown, but it has planar reflective optical capabilities and is exposed on a planar wavefront.

[0237] The first multicolor hologram 20 converts the spherical reconstructed wavefront 32 into a planar wavefront. The red component of the reconstructed wavefront 32 is reflected by the third hologram 180 to form a red reflected beam 38. The green component of the reconstructed wavefront 32 is reflected by the second hologram 160 to form a green reflected beam 36. Similarly, the blue component of the reconstructed wavefront 32 is reflected by the first hologram 140 to form a blue reflected beam 34.

[0238] The second multicolor hologram 22 then reflects beams 38, 36, and 34 to generate a planar redirected wavefront 46. Holograms 140, 160, and 180 of the second multicolor hologram reflect the blue beam 34, the green beam 36, and the red beam 38, respectively. This allows the planar wavefront 46 to primarily appear white. It can also have a color determined by the intensity of the reflected beams. Therefore, complex light redirection functions can be performed in a precise and compact manner.

[0239] List of reference numerals

[0240] 2. Master Stacking

[0241] 4 First Master Hologram

[0242] 6 Second Master Hologram

[0243] 8 Third Master Hologram

[0244] 10 Mother board

[0245] 12 Master Components

[0246] 14 First photosensitive layer

[0247] 16 Second photosensitive layer

[0248] 18 Third photosensitive layer

[0249] 20 First Multicolor Hologram

[0250] 22 Second Multicolor Hologram

[0251] 24 HOE

[0252] 26 Reference Beam

[0253] 28 Object Beams

[0254] 30 Optical Liquid

[0255] 32 Reconstructing the Wavefront

[0256] 34 Reflected waves in the first wavelength range

[0257] 36. Reflected waves in the second wavelength range

[0258] 38. Reflected waves in the third wavelength range

[0259] 40 meeting points

[0260] 42 Substrate

[0261] 43 Replica substrate

[0262] 44. Replication Stacking

[0263] 46 Redirecting wavefront

[0264] 48 Light source / radiation source

[0265] 50 UV radiation source

[0266] 140 First Replicated Hologram

[0267] 160 Second replicated hologram

[0268] 180 Third Replica Hologram

Claims

1. A method for replicating multicolor hologram stacks, comprising the following steps: a. Provide a first master hologram configured for a first wavelength range and a second master hologram configured for a second wavelength range. b. Provide a replication stack with a first photosensitive layer on the replication substrate. c. Expose the first master hologram with light within a first wavelength range to obtain a first replicated hologram in the first photosensitive layer. d. Fix the first replicated hologram in the first photosensitive layer. e. Apply a second photosensitive layer on top of the first photosensitive layer. f. Expose the second master hologram with light in a second wavelength range to obtain a second replicated hologram in the second photosensitive layer. g. Fix the second replicated hologram in the second photosensitive layer.

2. The method according to claim 1, characterized in that, The method further includes the following steps: h. Apply the third photosensitive layer to the second photosensitive layer. i. Provide a third master hologram configured for the third wavelength range. j. Expose the third master hologram using light in a third wavelength range to obtain a third replicated hologram in the third photosensitive layer. k. Fix the third replicated hologram in the third photosensitive layer.

3. The method according to any one of the preceding claims, characterized in that, The first master hologram and / or the second master hologram are disposed in a master stack, wherein the same master stack or master stacks with the same configuration are used to expose the first photosensitive layer and the second photosensitive layer.

4. The method according to any one of the preceding claims, characterized in that, Exposure using the first master hologram and / or the second master hologram occurs at the first exposure station and / or the second exposure station, respectively, wherein preferably, at each exposure station, the position of each master hologram relative to the replica stack in the longitudinal and / or lateral directions is adjusted.

5. The method according to any one of the preceding claims, characterized in that, The first master hologram and / or the second master hologram are provided in a master stack having a layered structure, wherein the first master hologram is present in a first layer and the second master hologram is present in a second layer, and In this process, the first replicated stack of photosensitive layers is applied, exposed, and fixed in a sequence that is mirror-symmetrical with respect to the layer structure of the master hologram.

6. The method according to any one of the preceding claims, wherein it is subordinate to claim 2, is characterized in that, One of the first wavelength range, the second wavelength range, or the third wavelength range corresponds to red light, one of the first wavelength range, the second wavelength range, or the third wavelength range corresponds to green light, and one of the first wavelength range, the second wavelength range, or the third wavelength range corresponds to blue light, and / or the first master hologram, the second master hologram, and the third master hologram are all reflection holograms.

7. The method according to any one of the preceding claims, characterized in that, The photosensitive layer comprises a photopolymer, wherein preferably, the photopolymer is sensitive to light in at least a first wavelength range and a second wavelength range.

8. The method according to any one of the preceding claims, characterized in that, The photosensitive layer is applied by adhesive bonding or by lamination, wherein the lamination is preferably performed by lamination rollers at a temperature of 20°C to 300°C and a pressure of 10N to 20,000N.

9. The method according to any one of claims 1 to 7, characterized in that, The application of the photosensitive layer includes coating with a liquid photopolymer and drying.

10. The method according to any one of the preceding claims, characterized in that, The replication substrate, the photosensitive layer, and / or the replication stack are present in the form of a roll of any length and / or conveyed on a traveling roll by a conveyor roller, wherein the replication method is preferably performed continuously.

11. The method according to any one of the preceding claims, characterized in that, The first master hologram and / or the second master hologram are disposed in a master stack including a master substrate, wherein the master substrate is positioned on the replication substrate of the replication stack, wherein preferably an optical adhesive film or optical liquid is applied between the master substrate and the replication substrate. Preferably, the replication substrate and / or the master substrate are provided with an anti-reflective coating.

12. The method according to any one of the preceding claims, wherein it is subordinate to claim 2, is characterized in that, in, Similarly, steps a through k are repeated to copy the multicolor hologram into the second replication stack using the fourth, fifth, and sixth master holograms. Preferably, the exposure of one of the two replica stacks is performed by a plane wavefront, and the exposure of the other of the two second replica stacks is performed by a spherical wavefront.

13. The method according to the preceding claims, characterized in that, The two replication stacks are connected to each other after the replication process, wherein the replication stacks are arranged at a distance of less than 1 mm, preferably less than 0.5 mm, and particularly preferably less than 0.1 mm.

14. A replica stack comprising at least a first replica hologram and a second replica hologram, the replica stack being capable of being produced by a method according to any one of the preceding claims.

Images