Method of replicating multicolor hologram by aligning master stack

Abstract

The invention relates to a method for replicating a multicolor hologram. The method includes providing a master stack including a first master hologram and a second master hologram arranged in a layered structure. The method further includes providing a replica stack and aligning the first master hologram relative to the replica stack by translating and / or rotating the master stack. The first master hologram is exposed to electromagnetic radiation of a first wavelength range so as to obtain a first replicated hologram in the replicated stack. Further, the method includes aligning the second master hologram relative to the replica stack by translating and / or rotating the master stack. The second master hologram is exposed to electromagnetic radiation of a second wavelength range to obtain a second replicated hologram in the replicated stack. The invention also relates to a replication stack which can be produced using the method according to the invention. The invention further relates to a master element and a device for carrying out the method according to the invention.

Description

Technical Field

[0001] This invention relates to a method for replicating a multicolor hologram. The method includes providing a master stack comprising a first master hologram and a second master hologram, the first and second master holograms being arranged in a layered structure and fixed in their relative positions to each other, wherein the first master hologram is configured for a first wavelength range and the second master hologram is configured for a second wavelength range. The method further includes providing a replication stack and aligning the first master hologram relative to the replication stack by translating the master stack in a longitudinal and / or lateral direction and / or by rotating the master stack. The first master hologram is exposed to electromagnetic radiation in the first wavelength range to obtain a first replicated hologram in the replication stack. The method further includes aligning the second master hologram relative to the replication stack by translating the master stack in a longitudinal and / or lateral direction and / or by rotating the master stack. The second master hologram is exposed to electromagnetic radiation in the second wavelength range to obtain a second replicated hologram in the replication stack.

[0002] The present 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 a method according to the invention. Furthermore, the present invention relates to a master element comprising a master stack and a substrate for performing the method according to the invention. The master stack includes a first master hologram and a second master hologram mounted on a substrate, wherein the master element includes an alignment module configured for translating and / or rotating the master stack relative to the substrate.

[0003] Furthermore, the present invention relates to an apparatus for replicating multicolor holograms, wherein the apparatus has an exposure module. The exposure module includes: a master stack including a first master hologram and a second master hologram, the first and second master holograms being arranged in a layered structure and fixed in relative positions to each other, wherein the first master hologram is configured for a first wavelength range and the second master hologram is configured for a second wavelength range; one or more exposure sources configured to direct electromagnetic radiation of the first and second wavelength ranges onto the master stack to replicate the first and second master holograms into a replication stack; and an alignment module configured to translate and / or rotate the master stack in a longitudinal and / or lateral direction prior to exposure by the one or more exposure sources to individually align the first and second master holograms relative to the replication stack. Background Technology

[0004] This invention relates to the field of hologram reproduction.

[0005] 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 diffraction of radiation at a single wavelength (monochromatic) or multiple wavelengths (polychromatic). In the case of polychromatic diffraction patterns, the master hologram is typically generated stepwise using lasers of different wavelengths. For this purpose, the diffraction pattern can be divided into color channels, which are simultaneously recorded in a single layer or each represents a separate layer of a multi-layer stack. 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 during the replication process. The master hologram can exist in the form of a thin film.

[0006] The master holograms used are typically mounted in or on a substrate body that carries the master hologram. The substrate body is preferably 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.

[0007] A master stack is exposed using a coherent light source to copy an image 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 preferably transported through various workstations to generate a HOE (holographic optical element).

[0008] During exposure, the composite roll is brought into optical contact with the surfaces of the master sheet stack. This "optical contact" should preferably allow a beam path to pass between the processing components without experiencing significant reflection or even total internal reflection. Direct material contact between the processing components is possible but not required. Preferably, neither reflection (especially total internal reflection) nor scattering occurs at the interface between the surfaces of adjacent processing components.

[0009] 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.

[0010] A 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.

[0011] 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, HOEs 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.

[0012] For some applications, it may be desirable for a HOE to be multilayered or to expose multiple superimposed patterns or wavelengths (e.g., color channels). In some cases, a hologram can contain a multicolor diffraction pattern in the form of Bragg gratings with different frequencies within a single layer of material. Such a hologram can be recorded simultaneously with multiple wavelengths, for example, as an RGB or CMY hologram. Multicolor holograms can be reproduced from multicolor RGB or CMY master holograms, which can be single-layered or stacked holograms with different wavelengths. This would require the use of photosensitive materials that are sensitive to all color channels used. However, such materials are often equally sensitive to all wavelengths and may not provide the highest image resolution across the entire wavelength range.

[0013] Multicolor holographic elements can also include multiple holograms that can be arranged in a stack. For example, a holographic element can exhibit multiple superimposed monochromatic holograms that have been recorded individually and combined with each other to form a stack. This allows for the use of photosensitive materials specifically configured for specific wavelengths or color channels and improves the quality of the HOE.

[0014] 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).

[0015] 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 concave mirror and a plane mirror. Advantageously, the arrangement of two holographic elements arranged adjacent to each other, which are at least partially reflective, allows for high refractive power while providing high image quality and a compact design.

[0016] However, precise positioning of the holographic layers relative to each other is necessary to avoid undesirable filter effects and ensure optical functionality.

[0017] In the case of multilayer holograms, it is crucial for the quality of the generated HOE that the stacked holograms are correctly positioned relative to each other. Depending on the complexity of the HOE, the number of layers in this stack can increase, which poses considerable challenges during the tuning steps of its production.

[0018] In an exemplary manufacturing method, a single multilayer photosensitive composite roll passes 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 photosensitive layers of different wavelengths, in which the master holograms of the color channels are replicated at their respective stations. To achieve perfect positioning of the holograms replicated in the layers of the composite roll, the flowing composite roll must be slowed down at precise locations at each station. This is extremely difficult to achieve with high repeatability due to the deformable nature of the composite roll.

[0019] Alternatively, multilayer composite rolls can also be exposed at a single workstation providing the master stack. Exposure can be performed sequentially for each desired wavelength. The flowing multilayer composite roll only needs to be slowed down once during exposure, which reduces the risk of errors due to misalignment and / or distortion. However, a disadvantage is that 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 rotation or offset due to the integration process, which particularly adversely affects the optical functionality of complex HOEs.

[0020] Another alternative is to use a single layer of photosensitive material to generate each layer of the HOE master stack within their respective composite rolls, and then combine the individual layers of the respective composite rolls into a stack. Due to technical limitations, the placement, lamination, and bonding of the layers are performed within tolerances, and these tolerances accumulate when the steps are repeated to generate stacks with two, three, four, or more layers.

[0021] 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.

[0022] This is complex. On the other hand, the lamination process of each layer itself can lead to alignment errors, for example, due to the different degrees of deformation of the layers.

[0023] Therefore, an alternative method is needed to generate multicolor holograms with high positional accuracy.

[0024] DE102010014305A1 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, bringing it into contact with and exposing it to at least one master hologram. One or more master surfaces may be simultaneously exposed to laser light over planar areas. 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.

[0025] The purpose of this invention

[0026] The object of this invention is to provide a method capable of reproducing multicolor holograms without the drawbacks of prior art. In particular, one object of this invention is to provide a method for reproducing 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 provide a reproduction method suitable for the continuous batch production of multicolor holograms with any degree of complexity, particularly for the production of multilayer HOEs. Summary of the Invention

[0027] This objective is achieved through the features of the independent claim. Advantageous embodiments of the invention are described in the dependent claims.

[0028] In a first aspect, the present invention relates to a method for replicating a multicolor hologram. The method includes the following steps:

[0029] a) Provides a master stack including a first master hologram and a second master hologram, the first master hologram and the second master hologram being arranged in a layered structure and fixed in their relative positions to each other, wherein the first master hologram is configured for a first wavelength range and the second master hologram is configured for a second wavelength range.

[0030] b) Provides replication stacking,

[0031] c) Aligning the first master hologram relative to the replica stack by translating the master stack in the vertical and / or horizontal directions and / or by rotating the master stack.

[0032] d) Expose the first master hologram to electromagnetic radiation in a first wavelength range to obtain the first replicated hologram in the replica stack.

[0033] e) Aligning the second master hologram relative to the replica stack by translating the master stack in the vertical and / or horizontal directions and / or by rotating the master stack.

[0034] f) Expose the second master hologram to electromagnetic radiation in a second wavelength range to obtain a second replica hologram in the replica stack.

[0035] The replication stack can preferably be provided in roll form and continuously passed through the stations of the replication method, making the method particularly suitable for mass production. Particularly advantageous is that the replication stack itself does not need to move between copies of the first and second master holograms. By providing the first and second master holograms within the layer structure of the master stack, exposure of the replication stack can advantageously be performed at a single workstation for the corresponding wavelength. Transmission-related distortions and positioning errors inherent in replication stacks can be avoided.

[0036] The ability to align the first and second master holograms separately relative to the replication stack also allows for the compensation of any positional variations between the holograms in a particularly efficient manner. The alignment of the second master hologram relative to the replication stack specifically means the alignment of the second master hologram relative to the first replica hologram present in the replication stack. In this way, the second master hologram can be positioned such that it precisely matches the position of the first hologram already exposed on the replication stack. This advantageously compensates for tolerances that may occur when integrating the first and second master holograms in the master stack. Similarly, positioning differences of the master holograms relative to the replication stack can also be avoided.

[0037] Another advantage is that the alignment of the second master hologram can be performed in the same manner each time the replication method is repeated. In this respect, any deviations in the sub-millimeter range that occur due to the transfer of the replication stack and / or the integration of the master hologram into the master stack can be compensated for by adjusting the master stack accordingly in a repeatable manner and with high precision.

[0038] By replicating a second master hologram in a replication stack, multicolor holograms with precisely aligned layers or channels can be created. These holograms exhibit exceptionally high quality, particularly because undesirable filtering effects between layers can be avoided. The advantage lies in the fact that any misalignment of the master holograms in the master stack is not replicated in the multicolor hologram. Instead, the possibility of independently aligning the first and second master holograms allows for optimized multicolor holograms, where the replicated holograms are reliably aligned with each other with high precision.

[0039] Since the first and second holograms exist within the master stack, they are fixed relative to each other. For each copy of the multicolor hologram, the alignment of the master holograms can be performed in the same manner. The first and second holograms cannot be freely shifted or rotated relative to each other, ensuring that no new positioning errors arise during the copying process that were not present during the production of the master stack. Instead, the same sequence of alignment steps can be reliably repeated. Therefore, the copying method can be easily performed with high positioning accuracy.

[0040] By providing a replication stack, photosensitive materials can be optically contacted with the master stack to produce a volume hologram. Advantageously, multiple color channels or wavelength channels can be exposed in a single or different photosensitive layers of the replication stack. Sequential exposure of the first and second master holograms can also preferably be performed in a single workstation, thereby improving the accuracy of the replication method. Preferably, the replication stack comprises different photosensitive layers sensitive to specific wavelength ranges of the electromagnetic spectrum.

[0041] Preferably, the replication involves progressively constructing a multicolor hologram within the replication system. For this purpose, a first master hologram and a second master hologram are replicated in a replication stack with corresponding photosensitive layers, wherein, as explained, the possibility of aligning the master holograms before each replication step allows for high-precision stack construction. Therefore, subsequent lamination of exposure layers to construct the replication stack and associated alignment errors can be avoided.

[0042] The replication stack can be provided as a roll and is provided with a carrier layer and / or a protective layer to protect the hologram replicated therein. Processing components (e.g., master stacks) can also be protected from unwanted residues (e.g., from photosensitive resin).

[0043] The alignment of the first master hologram with respect to the replication stack ensures the reliable reproducibility of the method. Therefore, previous replications can be performed by aligning the second (or nth) master hologram (and thus the entire master stack) with the replication stack. The first master hologram is then returned to its standard position above the replication stack through proper alignment. In this way, the diffraction pattern of the first master hologram can always be replicated on the replication stack with the desired orientation and position.

[0044] Since the master stack preferably includes a rigid master substrate on which or therein the master hologram is fixed, it is preferably more rigid than a flowing replication stack in the form of a foil. This allows the master hologram present on or in the master substrate to be positioned with a higher degree of repeatability than the case of a replication hologram in a foil-form replication stack.

[0045] In a preferred embodiment, alignment of the master stack relative to the replication stack can be ensured by providing a master element, which, in addition to the master stack, includes a separate substrate, wherein the master stack and the substrate are arranged to be movable relative to each other. During replication, the replication stack preferably contacts the substrate of the master element, such that alignment of the separate master stack, preferably in the form of a master substrate including a master hologram, can occur without any movement between the replication stack and the substrate. It is advantageous to completely avoid transferring stress or deformation to the replication stack by aligning the master hologram, since no relative movement is required at the interface between the replication stack and the master element.

[0046] Favorable contact between the substrate and the replication stack further stabilizes the replication stack and ensures it remains stationary during exposure of the first and second master holograms. Therefore, this method is particularly insensitive to the introduction of alignment errors in the replication stack, as it does not require alignment between exposure steps.

[0047] Since the same master stack can be used for different repetitions of the replication method, the master stack can also be adjusted to the same degree in the same way each time. This can be done more precisely than subsequently aligning multiple individually replicated holograms and layering them on top of each other to form a stack. In the latter case, each stack would have to be assembled separately after the replication method outside the replication system, for example by means of positioning markers, which is very complex. Instead, once the required positional adjustments of the first and second master holograms are determined, this can be repeated in the same way for each replicated multicolor hologram, so that a correctly aligned multicolor hologram is constructed during the replication method in the replication system. Advantageously, the alignment of the first and second master holograms can be pre-programmed. The procedure for aligning the master holograms can be determined by measuring the positional error between the master holograms in the master stack. This can be done in various ways, as described below.

[0048] By exposing the first hologram in the replication stack at a first wavelength, the first channel of the multicolor hologram can be exposed at the desired location in the replication stack. Due to its precise positioning and the elimination of the need to move the replication stack to another exposure station to expose additional channels, additional channels can be replicated at the exact desired location using a different wavelength, thereby compensating for alignment errors in the master stack. Therefore, the quality of the replicated multicolor hologram can advantageously exceed that of the master stack because any positional errors in the master hologram are compensated for in the replication method, as described above. Significantly higher quality can be achieved through a simple means of positioning multiple color channels or multiple layers relative to each other, compared to known methods in the prior art.

[0049] 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 one exposure of the corresponding master hologram, but may also include other preferred steps such as fixing, cutting, or trimming.

[0050] 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 passing through a DOE can be converted into almost 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.

[0051] "Configuration of the master hologram for a wavelength range" preferably means that the diffraction pattern 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 through the first master hologram are preferably given only for light within the first wavelength range. Light 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 light within the second wavelength range.

[0052] 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-overlapping ranges and are substantially non-overlapping. 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.

[0053] In the context of this invention, "wavelength range" can substantially include wavelengths of light, such as those emitted by a monochromatic laser.

[0054] 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.

[0055] 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 together. The "master stack" may be arranged within a master element, wherein, in a preferred embodiment, the master element comprises a master stack and a substrate.

[0056] In the context of this invention, the “layer structure” of the first and second (or additional) master holograms preferably describes the arrangement of the master holograms on or above each other. The master holograms arranged one above the other preferably exist on the same surface of the master substrate. For example, the first master hologram may be laminated onto the surface of the master substrate, while the second master hologram is applied onto the first master hologram. In a preferred embodiment, an additional layer exists on the layer structure consisting of the two master holograms. 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 replication stack without damaging the master holograms. 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 also the master hologram) relative to the substrate.

[0057] The “master substrate” is preferably a three-dimensional unit comprising a master hologram in a form that enables its processing and mobility. Specifically, the master hologram is contained in a fixed position by the master substrate such that any movement of the master substrate immediately results in a corresponding movement of the master hologram. 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, more preferably five times, and particularly preferably at least twenty times the size of the master hologram. The master substrate preferably has a regular shape that allows for a tessellated or linear arrangement.

[0058] 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.

[0059] 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, a transparent material is 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. Transparent materials (e.g., transparent master substrates or transparent covers) are particularly preferred if they are transmissive to light within the wavelength range exposed to the master hologram. Transparent materials can also be colored by selecting one or more specific wavelengths of light radiation.

[0060] Preferably, the surface or cover of the master stack comprises glass, PC, TAC, or PMMA. The surface material can be in the form of a film or plate to protect the master hologram. However, the surface or cover material can also be the material of the master substrate itself and can, for example, be in the form of a cuboid or cylindrical shape.

[0061] 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.

[0062] 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.

[0063] 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 20CCD 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 sensitivities of the layers may or may not overlap within the wavelength range as needed.

[0064] 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 irradiating the replication stack. The photosensitive layer may be in the form of a composite roll. In a preferred embodiment, the replication stack may 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.

[0065] In the context of this invention, a "replication substrate" is a component preferably 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 the 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, comprising a portion of a composite roll of two or more photosensitive layers 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 substrate and can be used as a substitute for the substrate substrate. 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 position multiple multicolor holograms vertically relative to each other and encapsulate them between substrates.

[0066] 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 configured 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.

[0067] 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.

[0068] 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 of the object beam and the reference beam within the hologram volume preferably generates a series of Bragg planes. Therefore, 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 illuminate 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 color hologram, each partial hologram can be reconstructed by recording only its colors. Therefore, 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.

[0069] Exposure can preferably be performed via an exposure module that provides one or more exposure sources for this purpose. For this purpose, the exposure source (also referred to as a "light source" in the context of this invention) preferably emits electromagnetic radiation in a first and / or second wavelength range. The electromagnetic radiation can preferably include infrared, visible, and / or ultraviolet radiation, with visible radiation being particularly preferred. In the context of this invention, UV radiation preferably refers to electromagnetic radiation in the range of 200 μm to 400 μm, and particularly preferably 300 μm to 400 μm. Visible radiation specifically refers to electromagnetic radiation in the range of 400 nm to 780 nm and infrared radiation in the range of 780 nm to 25 μm, preferably near-infrared, i.e., preferably 780 nm to 3000 nm, and particularly 780 nm to 1400 nm.

[0070] The light source preferably emits a coherent beam. Coherence essentially refers to the properties of light waves, thereby establishing a fixed phase relationship between two wave trains. Due to this fixed phase relationship, spatially stable interference patterns can occur. A distinction can be made between temporal and spatial coherence. Spatial coherence preferably represents 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 preferably represents a fixed phase relationship between wave trains along the propagation direction, and is given particularly for narrowband beams (preferably monochromatic beams).

[0071] The coherence length preferably refers to the maximum path length difference or runtime difference exhibited by two beams from their origin, such that their superposition still produces a stable interference pattern (in both space and time). The coherence time preferably refers to the time required for light to travel the coherence length.

[0072] 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.

[0073] 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, 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.

[0074] 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.

[0075] For reproductions with different wavelengths, particularly the first and second wavelength ranges, it is preferable to use illumination radiation within each different wavelength range, 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).

[0076] 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.

[0077] 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 to compensate 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°. The master hologram is aligned particularly relative to the replica stack, and therefore preferably aligned in a plane parallel to the replica stack.

[0078] 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 so that the replication stack moves into or out of the exposure station where exposure occurs.

[0079] 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.

[0080] 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, 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 it has a maximum or peak value at the center wavelength, which is a characteristic of that color. 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 has a center wavelength of approximately 630 nm.

[0081] It may also be preferred that one or more electromagnetic radiation channels correspond to radiation outside the visible spectrum, such as UV or IR radiation. Different channels may exist in the multicolor hologram in the form of diffraction structures, the diffraction patterns being configured to diffract electromagnetic radiation of their respective wavelengths or wavelength ranges. The diffraction patterns may exist in a single layer or different layers of the photosensitive material. This means that although the master stack includes multiple master holograms in different layers, these master holograms can all be replicated in the same photosensitive layer of the replication stack. However, the replication stack may also include multiple photosensitive layers, preferably arranged one above the other in a layered structure, and preferably reflecting the layered structure of the master stack.

[0082] In the context of this invention, a "photosensitive material" is 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 be achieved, for example, through the localized polymerization of monomers or shorter polymer chains, as in photopolymers.

[0083] In a preferred embodiment of the invention, a third master hologram is provided. The third master hologram may be part of a master stack including a first master hologram and a second master hologram. For example, the third master hologram may exist in a layered structure having a first master hologram and a second master hologram. The position of the third master hologram may be fixed relative to the first master hologram and the second master hologram.

[0084] In this case, multicolor holograms with a third copy hologram or a third (color) channel can be generated in the copy stack without having to move the copy stack to another exposure station.

[0085] In an alternative preferred embodiment of the invention, the third master hologram is provided separately from the master stacks of the first and second master holograms. The third master hologram may, for example, be disposed in another master stack, wherein this other master stack preferably includes another master substrate, such as a glass plate. Additional master stacks may optionally include additional master holograms, such as fourth, fifth, and further master holograms. Additional master stacks may also be disposed at the same exposure station as the first master stack, such that they are mounted in a rotatable and / or displaceable manner relative to the first master stack. Alternatively, additional master stacks may also be provided at downstream exposure stations.

[0086] Preferably, the method further includes the following steps:

[0087] g) Aligning the third master hologram relative to the replica stack by translating the master stack including the third master hologram in the longitudinal and / or lateral directions and / or by rotating the master stack including the third master hologram.

[0088] h) Expose the third master hologram to electromagnetic radiation in the third wavelength range to obtain the third replica hologram in the replica stack.

[0089] The master stack including the third master hologram can be the same master stack as the master stack including the first and second master holograms; similarly, as described above, it is preferable that the third master hologram is included in a separate, additional master stack. By adjusting the position of the third master hologram relative to the replica stack, its position relative to the already exposed first and second master holograms can be corrected. Therefore, positional errors of the third master hologram in the first master stack or the additional master stack, or positional errors of the first master stack or the additional master stack in the workstation, can be compensated. In this way, a multicolor hologram with three (color) channels can be produced, wherein the three (color) channels are aligned with each other with extremely high precision.

[0090] If the third master hologram is contained in the same master stack as the first and second master holograms, its position can be adjusted by translating or rotating the master stack. For each of the three master holograms, all three master holograms can be copied at the same workstation using the same three position settings. These settings can be repeated for each copy of the master stack, making the process particularly easy to automate.

[0091] On the other hand, if the third master hologram is provided in another master stack at another workstation, the replica stack including the first and second holograms is preferably positioned relative to the third master hologram before it is aligned. Therefore, it may be necessary to calculate or estimate the translational position of the third master hologram in the longitudinal direction separately for each replica. However, the alignment parameters used for rotation and translation in the lateral direction can remain the same between replicas. This is because the flowing composite fiber web forming or comprising the replica stack typically moves only in the longitudinal direction and not in the lateral direction.

[0092] In some multicolor HOEs (such as the wavefront manipulator in Figure 11 of DE102021116146A1), it has been found that larger tolerances for translational offsets between channels on a single axis (particularly the longitudinal axis) can be provided without significantly compromising the optical functionality of the HOE. In this way, multicolor holograms exposed at at least two wavelengths can be progressively constructed on multiple workstations. This offers several advantages, such as the possibility of continuously passing a replica stack through an intermediate processing station between exposures. The intermediate processing station may, for example, include a fixing module for fixing the exposed holograms in the replica stack and / or a coating module for applying additional photosensitive material layers to the replica stack. The intermediate station can also be used to add or remove films from the replica stack, for example, to remove optical adhesive films, protective films, or wavelength filter films. In this way, the replica stack can be stabilized in a separate intermediate station before further hologram exposures, thereby reducing the risk of replication errors and eliminating the need for wavelength-selective photosensitive materials for each channel.

[0093] 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.

[0094] In this way, multicolor RGB (red-green-blue) holograms can be created. Such holograms appear to diffract light from virtually the entire visible spectrum, thus generating high-resolution full-color holographic images. Due to the precise alignment of the channels, such images achieve very high visual quality. Multicolor RGB holograms can also redirect light from virtually all regions of the visible spectrum in a compact manner, which is particularly useful for HOEs integrated into cars, airplanes, or other vehicle windows.

[0095] In another preferred embodiment of the invention, a replica stack is provided as a first photosensitive layer in step b) of the method according to the invention. The first photosensitive layer (and any associated carrier or protective layer) is preferably temporarily laminated to a substrate in a removable manner. 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 substrate by rolling. Lamination can be performed using an optical adhesive film applied between the replica stack and the substrate. This can stabilize the composite roll during the duration of the exposure and / or fixing steps. The fixing steps can be pre-fixing, incremental fixing, or full fixing.

[0096] For the purposes of this invention, "pre-fixation" is preferably a treatment of the photosensitive material to reduce its sensitivity to further exposure via further electromagnetic radiation. Pre-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 pre-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.

[0097] In a preferred embodiment of the invention, each photosensitive layer of the replicated stack is pre-fixed after exposure. Preferably, pre-fixing is performed in situ without moving the replicated stack. Pre-fixing can sufficiently stabilize the exposed photosensitive layers to allow the application of another photosensitive layer on top without affecting the already replicated hologram. It is also preferable that the replicated multicolor hologram, comprising any number of layers, is fully fixed after all exposure steps. Full fixation can be performed in situ, particularly within the exposure station, without moving the replicated multicolor hologram. Alternatively or additionally, full fixation can be performed in a downstream fixation station. This fixation can be performed on the stationary replicated multicolor hologram or while the replicated multicolor hologram is being transported through the fixation 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.

[0098] In the following preferred embodiments, "fixing" preferably refers to the final step of completely fixing, pre-fixing, or fixing a pre-fixed photosensitive material.

[0099] Preferably, after exposure in step d), the first replicated hologram is fixed in the first photosensitive layer. Preferably, the fixing is performed without moving the first replicated hologram. This means that the exposure and fixing of the first hologram are preferably performed in a single workstation. The same workstation may preferably include an exposure module and a fixing module. Each module can be activated as needed for the corresponding process step, for example, by turning on the exposure source, UV lamp, heating lamp, etc. The module can be deactivated in process steps where it is not used.

[0100] By fixing the first hologram within the first photosensitive layer, there is no risk of affecting further exposure steps of the first hologram. This is particularly useful in the case of wavelength-selective photosensitive materials, since the wavelength ranges of such materials typically overlap. The first photosensitive layer may, but advantageously, need not exhibit wavelength selectivity.

[0101] After the first hologram has been fixed in the first photosensitive layer, a second photosensitive layer can preferably be added to the replication stack. The second photosensitive layer can be provided, for example, as a roll and applied to the layer structure of the replication stack by roll lamination. A second hologram can then be exposed in the second photosensitive layer. In this way, the photosensitive layer does not need to be wavelength selective, and subsequent exposure steps do not interfere with previous exposure steps. Simultaneously, after parallel exposure and lamination to form the layer structure, the individual layers do not need to be aligned with each other in a conventional manner. Instead, the first and second holograms are provided as a precisely aligned stack during exposure. Additional layers can be added to the replication stack upon request. Particularly error-free multicolor holograms can be produced.

[0102] In another preferred embodiment of the invention, fixation is performed after each exposure. Fixation is preferably performed by UV radiation, radiation in the visible light range of the electromagnetic spectrum, and / or heat treatment. Fixation can be performed using a fixation module, which is preferably located in the same workstation as the exposure module. In this way, both exposure and subsequent fixation can be performed in the same workstation where the hologram was exposed. This allows for the construction or provision of a stack of replicas, preferably at a single workstation, without the need to move the replicated holograms between method steps. This further prevents alignment errors.

[0103] By fixing the replicated holograms after exposure, they can be stabilized and insensitive to defects caused by interfering light or exposure of other layers. Furthermore, the fixed photosensitive layer can be moved to other workstations without deformation or shrinkage, such as with soft resin.

[0104] It is particularly advantageous to fix each hologram immediately after exposure to obtain a complete, aligned multicolor hologram stack without having to move the hologram stack from the workstation. This allows precisely aligned holograms of different layers to remain fixed in their relative positions during replication stacking. The resulting multicolor holograms are therefore largely error-free.

[0105] In a preferred embodiment of the invention, the translation and / or rotation of the master stack is controlled by a control unit. This allows translation and / or rotation to be performed with specific precision and repeatability.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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 the memory, alignment of the master holograms can be performed for repetition of the same exposure step sequence without recalculating the required alignment. The 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 portions of composite webs or unexposed replica stacks.

[0110] 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 on 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 be located on the replication stack or the substrate. Alternatively, the external alignment marks may exist only in software, for example, as predetermined image coordinates.

[0111] 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 translation and / or rotation positions to be tested can be repeatedly selected 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 the optimal value according to defined constraints. The convergence function used to select the optimal translation and / or rotation position can be, for example, based on an iterative or recursive algorithm.

[0112] 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.

[0113] In another preferred embodiment of the invention, in order to determine the desired degree and direction of translation and / or rotation of the first master hologram and / or the second master hologram, the master stack is illuminated with collimating 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.

[0114] Preferably, the desired degree and / or direction of translation and / or rotation of the first master hologram and / or the second master hologram 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 in the first or second master hologram can be used.

[0115] 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.

[0116] 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 can then be moved incrementally until the position of the positioning mark matches the target position. The positioning mark can take any form, such as an imprint, notch, or holographic element.

[0117] 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.

[0118] 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 slide that can be translated via two orthogonal axes, for example by means of pins, guides, etc. It may also be preferred that the slide is located on a rotatable carrier connected to a motor (e.g., a piezoelectric motor). Of course, additional pins, gears, or similar devices can be provided for fine adjustment and / or restriction of movement.

[0119] 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.

[0120] The master substrate is preferably configured to support a layered structure of 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, or prism. At least one surface of the master substrate is preferably parallel to the master hologram and intersects the longitudinal and transverse directions.

[0121] 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.

[0122] 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.

[0123] The master substrate or its cover can provide a rigid surface onto which optical fluid 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 aberration 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, a master stack including a first master hologram and a second master hologram is mounted on a substrate, wherein preferably, translation and / or rotation of the master stack relative to the substrate is performed to perform alignment. In the context of the invention, the master stack substrate is preferably part of the master element.

[0125] This allows for functional separation of the master stack and the substrate. The substrate can be specifically configured for optical contact with the replication stack. This advantageously allows the substrate to remain stationary during the various stages of exposure while the master stack can be aligned for optimal replication, as described. Advantageously, this prevents stress or deformation from being 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 parts of the master element, i.e., between the substrate and the master stack.

[0126] 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.

[0127] Furthermore, the substrate between the replica stack and the master stack allows for excellent optical contact, while the master stack is spaced apart from the replica 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 replica stack.

[0128] 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. Such undesirable reflections can constitute stray light, which can impair the quality of the reconstructed multicolor hologram. This is advantageously prevented in this case.

[0129] In a preferred embodiment of the invention, optical contact between the replication stack and the substrate is achieved through 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 may also include semi-solid substances such as gels or fluids such as optical liquids. 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.

[0130] 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 substrate, and / or master hologram, and improves the optical contact between them. The optical fluid has the advantage of enabling frictionless movement of the two components while allowing 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.

[0131] 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.

[0132] In another preferred embodiment of the invention, an optical fluid is introduced between the substrate and the replication stack to impart optical contact. The optical fluid 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 fluid can act as a lubricant to protect the substrate from surface damage.

[0133] 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.

[0134] 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.

[0135] 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. 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.

[0136] In the context 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.

[0137] 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.

[0138] In the context of this invention, "optical liquid" preferably refers to 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 liquid can prevent undesirable reflections at interfaces between components.

[0139] 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.

[0140] In another preferred embodiment of the invention, the replication stack includes a replication substrate. The replication substrate is preferably used to support the photosensitive layer of the replication stack to improve its handling.

[0141] In a preferred embodiment of the invention, the replica substrate is a rigid component. The rigid replica substrate preferably exhibits similar properties and dimensions to the base substrate. The same material can be used for this purpose, and a similar refractive index is preferably chosen, preferably between 1.4 and 1.6.

[0142] In some implementations, a rigid replication substrate can be used instead of a base substrate. In this way, the rigid replication substrate can be bonded to other layers of the replication stack and further processed using them. In this way, the substrate is separate for each multicolor hologram. The in-situ lamination of the optical adhesive film onto the substrate can be omitted, allowing for faster exposure. The need to clean the base substrate also becomes unnecessary; instead, the multicolor hologram can be constructed directly on the replication substrate and exhibits very good quality.

[0143] 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 roller-based stacking methods, which can lead to 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.

[0144] In other cases, 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.

[0145] A replication substrate ensures particularly good optical contact between the replication stack and the master stack. Similar to a substrate, the replication substrate can be used in combination with optical liquids or optical adhesive films without the risk of residue remaining on the replicated hologram itself. In embodiments using a replication substrate instead of a substrate, an optical liquid can be placed between the replication substrate and the master stack. This provides advantages similar to applying an optical fluid between the substrate and the master stack.

[0146] The replication substrate provides sufficient rigidity to the replication stack, allowing it to remain exceptionally stable during multi-step exposures. Furthermore, the strength and rigidity of the replication substrate allow for the lamination of additional layers and / or the removal of layers from the replication stack between exposure steps without undesirably deforming the stack. This supports incremental layer construction of the replication stack, enabling photosensitive layers to be exposed and fixed at the desired wavelength before the application of additional photosensitive layers. Therefore, even if the layers are not wavelength-selective, the exposure of subsequent layers does not necessarily impair the optical function of previous layers. This provides a particularly stable and error-free replication method.

[0147] 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.

[0148] In another preferred embodiment of the invention, the layer structure of the replica stack is arranged in a mirror-symmetric manner relative to the layer structure of the master stack. This mirror symmetry specifically relates to 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.

[0149] In another preferred embodiment of the invention, the replication stack is in the form of a roll of any length. This enables an efficient continuous replication process in which the web (also referred to as a “composite web”) is moved such that its different portions are located at different workstations. In this way, the exposed portions of the composite web can be secured, while the upstream portions of the composite web remain exposed. This securing can be achieved using a securing module at a securing station, which is preferably located downstream of the exposure station. This composite roll can also be provided in a compact and practical form as a roll, particularly if the thickness and flexibility of the replication stack are suitable for this. This makes it possible to easily transport the composite web through the replication process by unrolling and rolling up the composite roll.

[0150] In a preferred embodiment of the invention, an exposure module and a fixing module can be used to perform the exposure step and one or more fixing steps within the same workstation. This arrangement can reduce the process time for producing multicolor holograms. In such an embodiment, the exposure and fixing steps may not be performed simultaneously, but rather intermittently by operating the corresponding modules according to the method sequence. In such an embodiment, the replication stack can still be provided in roll form, where further processing upstream or downstream of the workstation is performed continuously in sync with the exposure and fixing. Such further processing may include removing the protective film, cutting dimensions, and / or combining the finished multicolor hologram with other multicolor holograms to form a HOE. Such a process can be performed with high throughput and reliable control.

[0151] Alternatively or additionally, the duplicated stack or duplicated substrate is conveyed on a conveyor belt via transfer rollers, wherein the duplication method is preferably performed continuously.

[0152] In a preferred embodiment of the invention, the photosensitive layers are pre-fixed before exposure to increase their mechanical stability. This pre-fixation may, for example, involve partial cross-linking of photopolymer molecules, thereby increasing the viscosity of the liquid layer while maintaining sufficient photosensitivity.

[0153] In another preferred embodiment of the invention, at least the first photosensitive layer is pre-fixed after the exposure of the first hologram and before the application of the second photosensitive layer. This protects the first photosensitive layer from mechanical deformation, such as during the lamination of the second photosensitive layer. Furthermore, it protects the first photosensitive layer from unwanted exposure. It is likely preferable that this pre-fixing occurs after each exposure step.

[0154] In another preferred embodiment of the invention, the replicated multicolor hologram is fully fixed after all the holograms contained therein have been exposed. Full fixation can also be performed in the exposure module to avoid mechanical movement of the multicolor hologram. Alternatively, full fixation can be performed in a separate workstation. This reduces processing time because the upstream portion of the roll-shaped replication stack can be exposed simultaneously in the exposure module.

[0155] In a preferred embodiment of the invention, the multicolor hologram is configured to perform the optical functions of an optical component such as a lens or mirror. The optical functions can be performed using a particularly compact, and especially inconspicuous, film-like component.

[0156] In another preferred embodiment of the invention, steps a) to f) of the method according to the invention described above are similarly repeated to replicate the second multicolor hologram in the second replication stack using a second master stack. By performing steps a) to f) at least twice with the first replication stack and the second replication stack, a first multicolor hologram and a second multicolor hologram can be generated.

[0157] Preferably, one of the first and second replica stacks is exposed using a planar 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 the spherical wavefront into a planar wavefront, and the other of the two multicolor holograms can be configured to reflect the planar waveform at a predetermined angle.

[0158] Multicolor holograms can perform the functions of concave or plane mirrors 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.

[0159] In another preferred embodiment of the invention, the first multicolor hologram and the second multicolor hologram are connected to each other, wherein the first multicolor hologram and the second multicolor hologram 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 multicolor hologram and the second multicolor hologram 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.

[0160] 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 is a major improvement over existing techniques, where six layers must be aligned and laminated one on top of the other to create such multi-layered RGB holograms. The accuracy of the HOE can be significantly improved. The resulting multicolor HOE can combine the functions of concave and planar mirrors to perform complex redirection of electromagnetic beams in a very compact manner.

[0161] In another aspect, the present invention relates to a replication stack comprising at least a first and a second replicated hologram capable of being produced by a method according to the invention. 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 replication stack can diffract radiation of two wavelengths. Additionally, the replication stack may include further layers, such as a carrier film, a protective layer, and / or a replication substrate.

[0162] This replication stack advantageously includes diffraction patterns configured to diffract radiation with two or more different wavelengths. The diffraction patterns corresponding to the 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.

[0163] In another aspect, the present invention relates to a master element for performing the method according to the invention, comprising a master stack and a substrate. The master stack includes a first master hologram and a second master hologram movably mounted on the substrate.

[0164] Preferably, the original stack also includes a master substrate, and the first master hologram and the second master hologram exist in a fixed manner on or in the master substrate.

[0165] Such master elements advantageously allow the master hologram to move relative to the substrate, ensuring alignment even after optical contact has been established between the substrate and the replication stack. Therefore, the position of the master hologram within the master element can be adjusted prior to exposure, allowing compensation during exposure for any positioning errors of the master hologram relative to each other or relative to the master substrate. Even if the master holograms of multilayer master elements contain unacceptable positioning tolerances due to their manufacturing methods, they can be used to produce multicolor holograms with significantly tighter tolerances.

[0166] The substrate can be specifically configured for optical contact with the replication stack. Unlike the master hologram, the substrate can advantageously remain stationary during the various stages of exposure. This ensures the stability of the replication method and prevents possible undesirable deformation of the photosensitive layer of the replication stack.

[0167] This means that during exposure, only the master stack needs to be moved to align the master hologram. The master stack can be particularly lightweight while maintaining sufficient rigidity. Where the replication stack is not directly laminated onto the master stack, the master substrate can exhibit slightly lower rigidity and mechanical strength than the substrate, and thus can be characterized by a lower thickness. Since the replication stack and / or the optical adhesive film as an intermediate layer are laminated onto the substrate rather than the master stack, only the substrate needs to withstand the lamination pressure in this case. Preferably, the master stack including the master substrate can be configured to be lighter and therefore can be moved with specific precision by an alignment module (e.g., via a piezoelectric motor) to perform alignment.

[0168] Preferably, the thickness of the substrate is selected to ensure sufficient mechanical stability during the application of replication stacking and / or photosensitive layers. Preferably, the thickness of the substrate is limited to keep the optical path between each photosensitive layer and the corresponding master hologram sufficiently small. This avoids unnecessary optical losses.

[0169] Preferably, the substrate has a length, width, and thickness. The length and width of the substrate are preferably chosen such that all areas of the master stack used are covered by the substrate. In other words, advantageously, the area of ​​the master stack is not located outside the substrate when the master stack is rotated or translated. Therefore, the length and / or width of the substrate can exceed the length and / or width of the master stack, with the excess portion being, for example, 1-3 mm.

[0170] The master element preferably further includes an alignment module configured for translation and / or rotation of the first master stack relative to the substrate.

[0171] The alignment module preferably includes a control unit, wherein the control unit is configured to automatically perform a predetermined translation and / or rotation of the first master stack for each alignment step in the replication series.

[0172] Automatic alignment with the control unit allows known alignment parameters of the master stack to be used for each repetition of the replication cycle without recalculation. The control unit can also be used to automatically adjust the speed of the alignment exposure step. This allows the translational or rotational movements required to align the first and second master holograms to be repeated synchronously with other aspects of the replication method. For example, the cycle of pre-programmed movements of the master stack can be synchronized with the cycle time for bringing the unexposed replication stack into contact with the substrate. This provides a very fast and continuous replication method for mass production of very high-quality multicolor holograms.

[0173] Preferably, translation and / or rotation can be performed with an accuracy of at least 10 μm and / or at least 0.1°. With such movement precision, even small alignment errors in the master hologram can be effectively compensated for, resulting in very high efficiency and sharpness of the obtained multicolor hologram.

[0174] In another aspect, the present invention relates to an apparatus for replicating a multicolor hologram in a method according to the invention. The apparatus comprises an exposure module including:

[0175] - A master stack including a first master hologram and a second master hologram, the first master hologram and the second master hologram being arranged in a layered structure and fixed in their relative positions to each other, wherein the first master hologram is configured for a first wavelength range and the second master hologram is configured for a second wavelength range;

[0176] One or more exposure sources are configured to direct electromagnetic radiation in a first wavelength range and a second wavelength range onto a master stack to copy a first master hologram and a second master hologram into a replication stack; and

[0177] - The alignment module is configured to translate and / or rotate the master stack in the longitudinal and / or lateral directions to align the first master hologram and the second master hologram relative to the copy stack before exposure by one or more exposure sources.

[0178] In the context of this invention, "module" preferably refers to a workstation in a continuous production method, which is preferably equipped with the technical means required to perform the method steps. Different modules may, but do not necessarily, be separated from each other by a housing or partition wall. In some embodiments of the invention, some modules are sub-units of other modules.

[0179] The exposure module preferably includes a master stack, an exposure source, and an alignment module within a housing, wherein the housing is preferably impermeable to light used in the exposure. The exposure module preferably has an inlet and an outlet for the replication stack to enter and exit the exposure module, respectively. The apparatus preferably also includes a conveying module for introducing the replication stack into the exposure module and for conveying the multicolor hologram out of the exposure module. Suitable embodiments of the transport module, such as transport rollers and / or transport belts, are known to those skilled in the art.

[0180] The "exposure source" preferably includes any type of radiation source configured to emit electromagnetic wavelengths within a first wavelength range and a second wavelength range. Preferably, a coherent light source, such as a laser, is used as the exposure source. Similar to the method according to the invention, the radiation from the exposure source can be modulated by an optical parametric oscillator and / or guided by suitable light redirection components (such as lenses, mirrors, prisms, etc.). Furthermore, the light redirection component can be equipped with a controllable actuator to guide the radiation onto the master stack at a predetermined angle. Additionally or alternatively, the exposure source itself can be equipped with an actuator to guide the radiation onto the master stack. Such an optical parametric oscillator, light redirection component, and / or actuator can also preferably be formed as part of an exposure module.

[0181] In a preferred embodiment of the invention, the device further includes a control unit configured to perform a predetermined translation and / or rotation of the master stack of the first master hologram and the second master hologram relative to the replication stack via an alignment module prior to exposure by one or more exposure sources, wherein the translation and / or rotation may preferably be performed with an accuracy of at least 10 μm and / or at least 0.1°.

[0182] In a preferred embodiment of the invention, the control unit is part of the alignment module, which does not mean that the device is preferably located inside the housing of the alignment module and must be spatially arranged with it. However, the control unit is preferably connected to the alignment module and / or an interface, particularly in connections for exchanging data or control signals, wherein the connection can be wireless or wired.

[0183] In a preferred embodiment of the device, the control unit is configured to control all steps of the replication method according to any embodiment of the invention. This control unit is preferably further connected to the exposure source and all associated actuators, transfer modules, lamination modules, coating modules, fixing modules, or any other operable components of the device.

[0184] In another preferred embodiment of the invention, the apparatus includes any module, component, or computer program product configured or required to perform method steps of a preferred embodiment of the replication method according to the invention.

[0185] In a preferred embodiment of the device, a master stack exists within master elements, wherein the master elements include a substrate. Preferably, the alignment module is configured to translate and / or rotate the master stack relative to the substrate. Such master elements advantageously allow the master hologram to move relative to the substrate, so that the master hologram can still be aligned after optical contact has been established between the substrate and the replication stack.

[0186] In another preferred embodiment, the device includes a lamination module, which is preferably configured to press the replica stack onto a substrate. By pressing the replica stack onto the substrate, a mechanically stable and optically seamless contact can be established between the replica stack and the master element. This reduces the risk of erroneous entry into the replica stack.

[0187] Alternatively or additionally, the lamination module is configured to apply an additional photosensitive layer to the replication stack. This is particularly preferred if the additional photosensitive layer is provided in solid form or on a solid carrier film.

[0188] In a preferred embodiment of the invention, the apparatus may include a coating module. This coating module is preferably configured to apply a new photosensitive material layer to the replication stack. Preferably, the coating module is located within the exposure module, such that the replication stack does not need to be moved from its position to be coated. However, it is also preferable that the coating module is disposed between the exposure modules, particularly for applying a third or additional photosensitive material layer to the replication stack.

[0189] In another preferred embodiment, the apparatus further includes a fixing module configured to fix at least one photosensitive layer of the replication stack, and preferably located within the housing of the exposure module. By inserting the fixing module into the housing of the exposure module, the replication stack or a portion thereof can be fixed or pre-fixed in situ. This prevents errors from being introduced into the replication method.

[0190] Preferably, the same fixing module is configurable in terms of its operating parameters, allowing it to be used for both pre-fixation and full fixation. Alternatively, the apparatus preferably comprises multiple fixing modules, with one or more fixing modules preferably located within the housing of the exposure module.

[0191] Terms such as substantially, approximately, about, nearly, close to, almost, etc., preferably describe tolerance ranges of less than ±20%, preferably less than ±10%, particularly preferably less than ±5%, and especially less than ±1%, and include precise values.

[0192] 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 stacks, master elements, and apparatus according to the invention, and vice versa.

[0193] Detailed description

[0194] The invention will now be explained in more detail with reference to examples and descriptions, but is not limited thereto. Attached Figure Description

[0195] Figure 1 It is a schematic diagram of a master stack structure that includes three master holograms.

[0196] Figure 2A It is a schematic diagram of the alignment of the first master hologram, so that its convergence point coincides with the reference point.

[0197] Figure 2B This is a schematic diagram of exposing the first master hologram onto the first photosensitive layer of the replication stack.

[0198] Figure 3A This is a schematic diagram showing the alignment of the convergence points of the second master hologram and the first master hologram.

[0199] Figure 3B This is a schematic diagram of exposing the second master hologram onto the second photosensitive layer of the replication stack.

[0200] Figure 4A This is a schematic diagram showing the alignment of the third master hologram with the convergence points of the first and second master holograms.

[0201] Figure 4B This is a schematic diagram of exposing the third master hologram onto the third photosensitive layer of the replicated stack.

[0202] Figure 5 An example replica stack including a multicolor z-hologram produced by the method according to the invention is shown. Detailed Implementation

[0203] Figure 1The 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.

[0204] A second master hologram 6 is laminated onto a stack including the master substrate 10 and the first master hologram 4. The second master hologram 6 is configured for a second wavelength range λ2, specifically the green range of the visible spectrum. Figure 1 As shown in the second illustration, during lamination, positional displacement may occur between the second master hologram 6 and the first master hologram 4. This means that the longitudinal, lateral, and / or rotational positions of the second master hologram 6 may not perfectly correspond to the longitudinal, lateral, and / or rotational positions of the first master hologram 4. Furthermore, the positions of the first master hologram 4 and the second master hologram 6 may not precisely correspond to their target positions on the master substrate 10.

[0205] The third master hologram 8 is then laminated onto the second master hologram 6, forming part of the layered structure of the resulting master stack 2. The third master hologram 8 corresponds to a third wavelength range λ3, such as the red range of the visible spectrum. Here, lamination also causes a shift, so that the position of the third master hologram 8 does not perfectly match the position of the first master hologram 4 or the second master hologram 6. 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 exhibit optical functions for focusing incident radiation.

[0206] The quality of the hologram reconstructed from or generated by the optical functions of the master stack 2 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, it is still possible to generate a multicolor hologram 20 with extremely low tolerances using a master stack 2 with high tolerances.

[0207] 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.

[0208] Figure 2A and Figure 2B The illustration shows the source Figure 1 The 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.

[0209] 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 coating 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 a light beam 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 2A to 2B 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.

[0210] 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 3A and Figure 4A 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.

[0211] The position of the master hologram 4 can also be adjusted relative to the position of the underlying substrate 42. For example, as Figure 2A As illustrated, the master hologram 4 can be centered directly above the substrate 42 with a predetermined margin.

[0212] 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 2B 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, 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 encompassing the blue range of the spectrum) and performs the optical function of converting a spherical wavefront into a planar wavefront. Optionally, the first hologram 140 can be fixed (not shown) before performing further exposure steps. This can be done by activating a fixing module in the same workstation.

[0213] Figure 3A and Figure 3B The step of replicating the second hologram corresponding to the green channel is schematically illustrated. The positions of the replica stack 44 and the substrate 42 preferably remain unchanged. Figure 3A As shown, the second master hologram 6 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 roll lamination. To perform this lamination, the substrate 42 is preferably sufficiently rigid and stably fixed. Exposure can then be performed by guiding a green reference beam 26 onto the second master hologram 6. A green laser can be used for this purpose. The reference beam 26 is reflected by the second master hologram 6 and forms an object beam 28 converging at a convergence point 40. The absolute position of the 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 and form a second hologram 160. This can be fixed before further exposure.

[0214] Similarly, the third master hologram 8 can be aligned and brought into the target location according to predetermined instructions, such as... Figure 4A 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 onto the third master hologram 8 using a red laser, and a third hologram 180 can be generated in the replication stack 44. The third hologram 180 is also fixed before further processing. Thus, the replication stack 44 comprises a multicolor RGB hologram. In this way, all three channels of the multicolor hologram are precisely aligned with each other, as shown at the same position of the convergence point 40 at each exposure step. This is possible despite the alignment errors that exist in the master stack 2 using the method according to the invention.

[0215] The exposed and preferably fixed multicolor hologram can be layered from a rigid substrate 42 to obtain a flexible multicolor hologram, or the substrate 42 can be used as a rigid replication substrate to obtain a stable multicolor hologram. The rigid replication substrate may have been positioned on top of the substrate and / or another multicolor hologram used in the application to encapsulate the replicated hologram between the two rigid replication substrates.

[0216] Figure 5 A HOE including 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 z-hologram has, for example, a BGRRGB layer structure. While the first multicolor hologram 20 is as follows... Figures 2A to 2B The second multicolor hologram 22 is generated as shown, but it has planar reflective optical capabilities and is exposed on a planar wavefront.

[0217] 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 red reflected beam 36. Similarly, the blue component of the reconstructed wavefront 32 is reflected by the first hologram 140 to form a red reflected beam 34.

[0218] 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.

[0219] List of reference numerals

[0220] 2. Master Stacking

[0221] 4 First Master Hologram

[0222] 6 Second Master Hologram

[0223] 8 Third Master Hologram

[0224] 10 Mother board

[0225] 12 Master Components

[0226] 14 First photosensitive layer

[0227] 16 Second photosensitive layer

[0228] 18 Third photosensitive layer

[0229] 20 First Multicolor Hologram

[0230] 22 Second Multicolor Hologram

[0231] 24 HOE

[0232] 26 Reference Beam

[0233] 28 Object Beams

[0234] 30 Optical Liquid

[0235] 32 Reconstructing the Wavefront

[0236] 34 Reflected waves in the first wavelength range

[0237] 36. Reflected waves in the second wavelength range

[0238] 38. Reflected waves in the third wavelength range

[0239] 40 meeting points

[0240] 42 Substrate

[0241] 44. Replication Stacking

[0242] 46 Redirecting wavefront

[0243] 140 First Replicated Hologram

[0244] 160 Second replicated hologram

[0245] 180 Third Replica Hologram

Claims

1. A method for replicating a multicolor hologram (20), comprising the following steps: a) A master stack (2) is provided, comprising a first master hologram (4) and a second master hologram (6), the first master hologram (4) and the second master hologram (6) being arranged in a layered structure and fixed in their relative positions to each other, wherein the first master hologram (4) is configured for a first wavelength range (λ1) and the second master hologram (6) is configured for a second wavelength range (λ2). b) Provides a replica stack (44). c) Aligning the first master hologram (4) relative to the replica stack (44) by translating the master stack (2) in the longitudinal and / or lateral directions and / or by rotating the master stack (2). d) Expose the first master hologram (4) to electromagnetic radiation in the first wavelength range (λ1) to obtain the first replicated hologram (140) in the replicated stack (44). e) Aligning the second master hologram (6) relative to the replica stack (44) by translating the master stack (2) in the longitudinal and / or lateral directions and / or by rotating the master stack (2), f) Expose the second master hologram (6) by electromagnetic radiation in the second wavelength range (λ2) to obtain the second replicated hologram (160) in the replicated stack (44).

2. The method according to claim 1, characterized in that, A third master hologram (8) is provided, wherein the third master hologram (8) is composed of the master stack (2) including the first master hologram (4) and the second master hologram (6), or another master stack, and the method includes the following additional steps: g) Aligning the third master hologram (8) relative to the replica stack (44) by translating the master stack (2) and / or the other master stack in the longitudinal and / or lateral directions, and / or by rotating the master stack (2) and / or the other master stack. h) Expose the third master hologram (8) to electromagnetic radiation in the third wavelength range (λ3) to obtain the third replicated hologram (180) in the replicated stack (44).

3. The method according to the preceding claim, characterized in that, One of the wavelength ranges (λ1), (λ2), or (λ3) corresponds to red light, one of the wavelength ranges (λ1), (λ2), or (λ3) corresponds to green light, and one of the wavelength ranges (λ1), (λ2), or (λ3) corresponds to blue light, and / or the first master hologram (4), the second master hologram (6), and the third master hologram (8) are reflection holograms.

4. The method according to any one of the preceding claims, characterized in that, The replication stack (44) is provided with a first photosensitive layer (14) in step b), and after exposure in step d), the first replicated hologram (140) is fixed in the first photosensitive layer (14).

5. The method according to any one of the preceding claims, characterized in that, After each exposure, fixation is preferably performed by UV radiation, radiation in the visible light range of the electromagnetic spectrum, and / or heat treatment.

6. The method according to any one of the preceding claims, characterized in that, Reference values ​​for the degree and direction of the desired translation and / or rotation of the first master hologram (4) and the second master hologram (6) are stored in memory and are automatically repeated by the control unit for a series of replica stacks (44).

7. The method according to the preceding claim, characterized in that, To determine the desired translation and / or rotation of the first master hologram (4) and / or the second master hologram (6), the master stack (2) is irradiated with collimated reconstruction radiation (32) to generate a convergence point (40), wherein the desired translation and / or rotation of the first master hologram and / or the second master hologram (2) is selected such that the convergence point (40) of the reconstruction radiation (32) for the first wavelength range (λ1) coincides with the convergence point (40) of the reconstruction radiation for the second wavelength range (λ2).

8. The method according to any one of the preceding claims, characterized in that, The first master hologram (4) and the second master hologram (6) are arranged in or on the master substrate (10) to form the master stack (2), wherein the master substrate (10) is translated and / or rotated by the alignment module to perform alignment.

9. The method according to any one of the preceding claims, characterized in that, The master stack (2), including the first master hologram (4) and the second master hologram (6), is mounted on a substrate (42), wherein translation and / or rotation of the master stack (2) relative to the substrate (42) are performed to perform alignment.

10. The method according to any one of the preceding claims, characterized in that, The master stack (2), including the first master hologram (4) and the second master hologram (6), is mounted on a substrate (42), wherein the substrate (42) comprises optical glass and / or optical plastic.

11. The method according to any one of the preceding claims, characterized in that, The replication stack (44) includes a replication substrate, and the master stack (2) is mounted on a substrate (42), wherein the replication substrate is positioned on the substrate (42) for exposure, wherein preferably, an optical adhesive film or optical liquid (30) is applied between the substrate (42) and the replication substrate, wherein preferably, the replication substrate and / or the substrate (42) are provided with an anti-reflective coating.

12. The method according to any one of the preceding claims, characterized in that, During the exposure step, the layer structure of the copy stack (44) is arranged in a mirror-symmetric manner relative to the layer structure of the master stack (2).

13. The method according to any one of the preceding claims, characterized in that, The replication substrate (44), photosensitive layer, and / or replication stack are present in the form of a roll of any length and / or conveyed in a flow path by a conveyor roller, wherein the replication method is preferably performed continuously.

14. The method according to any one of the preceding claims, characterized in that, Steps a) through f) generate the first multicolor hologram (20) in the first copy stack (44). Similarly, steps a) through f) are repeated to copy the second multicolor hologram (22) into the second copy stack (44) using the second master stack (2). Preferably, the exposure of one of the replica stacks in the first replica stack or the second replica stack (44) is performed by a plane wave front, and the exposure of the other replica stack in the first replica stack or the second replica stack (44) is performed by a spherical wave front.

15. The method according to the preceding claim, characterized in that, The first multicolor hologram (20) and the second multicolor hologram (22) are connected to each other, wherein the first multicolor hologram (20) and the second multicolor hologram (22) are arranged at a distance of less than 1 mm, preferably less than 0.5 mm, and particularly preferably less than 0.1 mm.

16. A replica stack (44) comprising at least a first replica hologram (140) and a second replica hologram (160) capable of being produced by the method according to any one of the preceding claims.

17. A master element (12) comprising a master stack (2) and a substrate (42) for performing the method according to any one of claims 1-15, characterized in that, The master stack (2) includes a first master hologram (4) and a second master hologram (6) mounted on the substrate (42), wherein the master element (12) preferably includes an alignment module configured for translation and / or rotation of the master stack (2) relative to the substrate (42).

18. The master element (12) according to the preceding claim, characterized in that, The alignment module includes a control unit configured to automatically perform a predetermined translation and / or rotation of the master stack (2) for each alignment step in the replication series, wherein the translation and / or rotation can preferably be performed with an accuracy of at least 10 μm and / or at least 0.1°.

19. An apparatus for replicating a multicolor hologram (20) in a method according to any one of claims 1-15, wherein the apparatus has an exposure module comprising: - Master stack (2), the master stack (2) includes a first master hologram (4) and a second master hologram (6), the first master hologram (4) and the second master hologram (6) are arranged in a layered structure and fixed in their relative positions to each other, wherein the first master hologram (4) is configured for a first wavelength range (λ1) and the second master hologram (6) is configured for a second wavelength range (λ2); - One or more exposure sources, the one or more exposure sources being configured to: direct electromagnetic radiation of the first wavelength range (λ1) and the second wavelength range (λ2) onto the master stack in order to copy the first master hologram (4) and the second master hologram (6) into the replication stack (44); as well as - Alignment module, which is configured to translate the master stack (2) in the longitudinal and / or lateral directions and / or rotate the master stack (2) before exposure by the one or more exposure sources, so that the first master hologram (4) and the second master hologram (6) are aligned relative to the copy stack (44).

20. The apparatus for replicating a multicolor hologram (20) according to the preceding claim, characterized in that, The device also has a control unit configured to perform a predetermined translation and / or rotation of the master stack (2) of the first master hologram (4) and the second master hologram (6) relative to the replica stack (44) via the alignment module before exposure to one or more exposure sources, wherein the translation and / or rotation may preferably be performed with an accuracy of at least 10 μm and / or at least 0.1°.

21. The apparatus (20) for replicating a multicolor hologram according to claim 19 or 20, characterized in that, The master stack (2) exists within the master element (12), wherein the master element (12) includes a substrate (42), and The alignment module is configured to translate and / or rotate the master stack (2) relative to the substrate (42).

22. The apparatus for replicating a multicolor hologram (20) according to the preceding claim, characterized in that, The device includes a lamination module, wherein the lamination module is preferably configured to laminate the replication stack (44) onto the substrate.

23. The apparatus for replicating a multicolor hologram (20) according to any one of claims 19-22, characterized in that, The device further includes a fixing module, wherein the fixing module is configured to fix at least one photosensitive layer of the replication stack, and is preferably present in the housing of the exposure module.

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