Method for the simultaneous replication of a multilayer polychromatic hologram

Abstract

The invention relates to a method for the replication of a polychromatic hologram. The method comprises: providing a master assembly comprising a first master hologram and a second master hologram, wherein the first master hologram is wavelength-selective for radiation having a first wavelength range and the second master hologram is wavelength-selective for radiation having a second wavelength range; providing a replication assembly comprising a first and a second light-sensitive layer, wherein the first light-sensitive layer is sensitive to radiation in the first wavelength range but not to radiation in the second wavelength range, and wherein the second light-sensitive layer is sensitive to radiation in the second wavelength range but not to radiation in the first wavelength range; and exposing the master assembly comprising the first and the second master hologram in order to replicate a first and a second hologram in the first and second light-sensitive layer, preferably simultaneously.

Description

[0001] “METHOD FOR THE SIMULTANEOUS REPLICATION OF A MULTILAYER POLYCHROMATIC HOLOGRAM”

[0002] DESCRIPTION

[0003] The invention relates to a method for replicating a polychromatic hologram. The method comprises providing a master composite comprising a first master hologram and a second master hologram, wherein the first master hologram is wavelength-selective for radiation having a first wavelength range and the second master hologram is wavelength-selective for radiation having a second wavelength range; providing a replication composite comprising a first and second light-sensitive layer, wherein the first light-sensitive layer is sensitive to radiation in the first wavelength range but not to radiation in the second wavelength range, and wherein the second light-sensitive layer is sensitive to radiation in the second wavelength range but not to radiation in the first wavelength range; and exposing the master composite comprising the first and second master holograms.to replicate a first and a second hologram into the first and second light-sensitive layers, preferably simultaneously.

[0004] The invention also relates to a replication composite comprising at least a first and a second replicated hologram producible by the method according to the invention.

[0005] Background and state of the art

[0006] The invention relates to the field of hologram replication.

[0007] Holograms are created by the interference of a reference beam with light reflected or diffracted from the surface of an object (object rays). Traditionally, three-dimensional objects have been used to create unique, customized holograms. Commercially available holograms, however, are often mass-produced using duplication processes. Such duplication processes typically use a master hologram, which has a diffraction pattern to be copied. The diffraction pattern can be configured to diffract radiation from a single, narrow wavelength range (monochromatic) or from multiple wavelength ranges (polychromatic). In the case of a polychromatic diffraction pattern, a master hologram is often created stepwise using lasers of different wavelengths.For this purpose, the diffraction pattern can be divided into color channels, which are recorded in a single layer as a multiplex or each represent a separate layer of a multilayer stack. The master holograms can be in the form of a thin film.

[0008] The master holograms used are often stored in or on a substrate body that bears the master hologram. The substrate body is preferably transparent and can have various shapes, such as a cuboid, a plate, or a cylinder. The combination of the master hologram (or master holograms) with the substrate body forms a master composite.

[0009] The master composite is exposed to a coherent exposure source to replicate the image from the master hologram into a photosensitive material. The photosensitive material is provided, for example, as a photosensitive composite with one or more carrier films. The photosensitive material is typically sensitive to a broad range of the electromagnetic spectrum, so that a master hologram exposed to different light colors can be multiplexed into a single photosensitive layer. For mass production, the photosensitive composite can be provided in the form of a flowing web comprising a photosensitive material and one or more carrier and / or protective layers.For this purpose, the light-sensitive web is preferably transported through various workstations to produce the HOEs (Holographic Optical Elements).

[0010] During exposure, the light-sensitive composite web is brought into optical contact with a surface of the master composite. "Optical contact" should ideally allow a ray of light to pass between process components without experiencing significant reflections or even total internal reflection. Direct, integral contact between the process components is possible, but not necessary. Preferably, neither reflection (especially total internal reflection) nor scattering occurs at the interface between the surfaces of adjacent process components.

[0011] To create a reflection hologram, the coherent light can traverse the composite path before reaching the master hologram, which reflects it back into the composite path. The object and reference beams interfere with each other in the light-sensitive material, forming the replicated hologram. The replication process is sensitive to changes in exposure angle, intensity, wavelength, etc., which must be adjusted according to the optical function of the master hologram. Typically, the exposure for each master hologram is performed according to a set of preprogrammed parameters.

[0012] HOEs (holographic optical elements) typically refer to optical components in which holographic properties are used to achieve a specific beam path of light, such as transmission, reflection, diffraction, scattering and / or deflection, etc. This allows the desired optical functionalities to be implemented compactly in any substrate. The holographic properties preferably exploit the wave nature of light, in particular coherence and interference effects. Both the intensity and the phase of the light are taken into account. For example, HOEs can be configured to fulfill the optical function of a classic optical component such as a lens or a mirror. However, due to their thin structure, they can be much more compact than conventional optical components.Furthermore, HOEs can be designed to avoid the well-known optical errors of conventional optical components, such as spherical and chromatic aberration. For example, HOEs can convert a plane wavefront into a spherical one and vice versa. They require very little space and can be easily integrated into a surface such as a window, eyeglasses, a card, or other product surfaces.

[0013] For some applications, it may be desirable for the HOEs to be exposed in multiple layers or with multiple superimposed patterns or wavelengths (e.g., color channels). A polychromatic multiplex hologram can contain diffraction structures in the form of Bragg gratings with different frequencies in a single material layer. Such a hologram can be recorded simultaneously at multiple wavelengths, for example, as an RGB or CMY hologram. The polychromatic hologram can be copied from a polychromatic RGB or CMY master hologram, which can be present in a single layer or as a stack of master holograms with different wavelengths. This would require the use of a light-sensitive material sensitive to all wavelengths used. However, such materials are often not equally sensitive to all wavelengths and offer only limited image resolution.The uneven wavelength sensitivity can lead to a reduction in the quality of the reproduced holograms.

[0014] A polychromatic hologram can be replicated using known light-sensitive materials in a single light-sensitive layer. The replicated hologram, comprising the various color channels in a single layer, is called a "multiplex." Although such multiplex holograms are thin, they have the disadvantage that their efficiency is reduced compared to a multilayer hologram. This can be attributed, among other things, to a mismatch between the light sensitivity profile of the light-sensitive material and the wavelength profile of the illumination source. Furthermore, with a multiplex hologram, there is generally an increased risk of crosstalk between the hologram channels.

[0015] Another explanation for the limited performance of multiplexed holograms is the use of the same potential refractive index modulation Δn for all color channels, so that each exposed color channel uses a fraction of the total refractive index modulation Δn. This may be due, for example, to the use of a light-sensitive photopolymer that has a specific concentration of monomers that can polymerize upon exposure. When light of different colors is used to polymerize the monomers, the light of each color is only allowed to polymerize a fraction of the total available monomers in the photosensitive material. Thus, with exposure in red, green, and blue, each of the three colors can ideally use one-third of the available monomers.Thus, a lower concentration of monomers is available for each color when all colors are multiplexed in a single layer than would be the case if a separate photosensitive material were provided for each color.

[0016] To create such a multiplex hologram, a composite web comprising a light-sensitive material can be brought to various exposure stations, with each exposure station containing a master element and an exposure source of a specific wavelength range. To align the various color channels in the composite web, it must be transported to the various stations with very close tolerances and brought into optical contact with the various master elements. Alternatively, the composite web would have to contact several master holograms (e.g., arranged as rollers) at a very precise speed. In practice, this is extremely difficult to achieve and can lead to errors in the positioning of the composite web relative to the successive master elements.For example, the different exposed color channels in the composite web may exhibit a twist or offset, which adversely affects the optical function of the HOEs.

[0017] A polychromatic holographic element can also comprise multiple holograms arranged one on top of the other in a stack. For example, a holographic element can have a plurality of superimposed monochromatic holograms, each recorded separately using light from different wavelength ranges and combined into a stack. This enables the use of light-sensitive materials designed for a broad range of the electromagnetic spectrum without the efficiency losses of a multiplex hologram. Creating these multilayer holograms previously required precise positioning of the various layers on the respective master hologram and then on top of each other. The equipment used for this often has large tolerances, which can lead to quality losses.For example, in a braking device for placing the corresponding section of a composite web at an exposure station which includes a master hologram, unavoidable errors occur, e.g. due to unintentional stretching of the composite web.

[0018] Such polychromatic holographic elements are used in many areas, such as in transparent displays (e.g. in shop windows, refrigerated cabinets, vehicle windows), for lighting applications such as information or warning signals in glass surfaces, light-sensitive detection systems, for example for interior monitoring (eye tracking in vehicles or presence status tracking of people indoors).

[0019] For example, DE102021116146A1 discloses a polychromatic hologram comprising six monochromatic layers in a single stack. The layers are configured for different wavelength ranges. Three upper layers can form a first holographic element configured to convert an upward spherical wavefront into a downward plane wavefront by reflecting light from the blue, green, and red parts of the electromagnetic spectrum at predetermined angles. Three lower layers form a second holographic element configured to reflect the downward plane wavefront back upward to create a plane wavefront at a predetermined angle. In this way, the layers of the two holographic elements can function like a combination of a concave and a plane mirror.Advantageously, by arranging two at least partially reflective multilayer holographic elements directly one behind the other, a high refractive power can be achieved, while at the same time providing high image quality and a compact structure.

[0020] However, precise positioning of the holographic layers relative to each other is necessary to avoid unwanted filter effects and ensure the optical function.

[0021] With multilayer holograms, it is crucial for the quality of the produced HOE that the superimposed holograms in a stack are correctly positioned relative to each other. Depending on the complexity of the HOE, the number of layers in such a stack can increase, which poses a significant challenge during the alignment steps of their production.

[0022] When exposing each layer of an HOE in a respective composite web, the individual layers must then be combined into a stack. Due to technical limitations, the placement, lamination, and bonding of the layers are carried out within tolerances, which also accumulate when the steps are repeated to create a stack with two, three, four, or more layers.

[0023] JPH11272153A discloses the use of positioning marks to align different layers of a hologram stack. According to this document, a multilayer hologram is produced from a plurality of layers of light-sensitive material. Holograms with different properties are recorded in each layer of light-sensitive material, and positioning marks are holographically recorded in each of the multiple hologram layers. The positioning marks are then used to align the layers on a substrate and laminate them together.

[0024] This is, on the one hand, complex. Furthermore, the process of laminating the layers itself can lead to alignment errors, for example, due to varying degrees of deformation of the layers.

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

[0026] Object of the invention The object of the invention is to provide a method and a replication network which enable the replication of a polychromatic hologram without the disadvantages of the prior art. In particular, it is an object of the invention to provide a method for replicating a polychromatic hologram in which several color channels or patterns with different wavelengths are positioned relative to one another in a holographic element using simple means, repeatably, and with high precision. Furthermore, it is a particular object of the invention to provide a replication method which is suitable for the continuous mass production of a polychromatic hologram of any degree of complexity, in particular for the production of a multilayer polychromatic hologram.Furthermore, it is an object of the invention to provide a replication array with precisely aligned color channels without the efficiency losses of a multiplex hologram.

[0027] Summary of the invention

[0028] The object is achieved by the features of the independent claims. Advantageous embodiments of the invention are described in the dependent claims.

[0029] In a first aspect, the invention relates to a method for replicating a polychromatic hologram. The method comprises the following steps: a) providing a master composite comprising a first master hologram and a second master hologram, wherein the first master hologram is wavelength-selective for radiation having a first wavelength range and the second master hologram is wavelength-selective for radiation having a second wavelength range; b) providing a replication composite comprising a first and second light-sensitive layer, wherein the first light-sensitive layer is sensitive to radiation in the first wavelength range but not to radiation in the second wavelength range, and wherein the second light-sensitive layer is sensitive to radiation in the second wavelength range but not to radiation in the first wavelength range;c) exposing the master composite comprising the first and second master holograms to replicate a first and a second hologram in the first and second photosensitive layers.

[0030] The replication composite can preferably be provided in roll form and pass through the station(s) of a replication process continuously or intermittently, making the process particularly suitable for mass production. A particularly advantageous feature is that the replication composite itself does not need to be moved between replications of the first and second master holograms. By providing the first and second master holograms in the layer structure of a master composite, the exposure of a replication composite can advantageously take place at a single workstation for the corresponding wavelengths. Transport-related deformations and positioning errors of the replication composite can be avoided. The replication process therefore avoids the introduction of alignment errors between the first and second holograms (also referred to as "partial holograms" within the meaning of the invention).

[0031] The exposure of the first and second master holograms in a single station advantageously means that the first and second master holograms can be exposed simultaneously or one after the other without intermediate opto- / thermochemical steps. The same exposure source can preferably expose both master holograms simultaneously, with the exposure source emitting radiation from both the first and second wavelength ranges. Each master hologram can select and reflect and / or diffract a wavelength range. Due to the wavelength selectivity of the light-sensitive layers, crosstalk between the wavelength ranges can be avoided. This means that the first master hologram is not replicated in the second light-sensitive layer, and vice versa.A motif that is intended to be reproduced only in the first wavelength range and only in the first light-sensitive layer will thus not be present as an unwanted "shadow" in the second light-sensitive layer. This allows a clear image with the correct weighting of the wavelength ranges to be created.

[0032] By providing a replication composite with a first light-sensitive layer sensitive to radiation in the first wavelength range and a second light-sensitive layer sensitive to radiation in the second wavelength range, the first and second holograms can be replicated in a single exposure process, preferably simultaneously. This process is extremely fast and efficient, without having to bring the replication composite into contact with different master composites. Since the light-sensitive layers react selectively to radiation of specific wavelengths, they can both be exposed with the same broadband exposure source, with an exposure source emitting radiation in different wavelength ranges, such as an RGB laser, or with multiple simultaneous or staggered scanning exposure sources.The multiple exposure sources can be designed for different wavelength ranges. The choice of one or more exposure sources can preferably depend on whether the holograms of different wavelength ranges are to be exposed from the same exposure angle.

[0033] If the first and second master holograms are configured for exposure from different angles, it is advantageous to use different exposure sources to replicate them. One advantage of the present invention is that the two or more exposure sources can be activated simultaneously without causing crosstalk in the replicated holograms. The two or more exposure sources can simultaneously illuminate the master composite over a large area from different angles. Alternatively, the two or more exposure sources can simultaneously scan the master composite from different angles. In other possible variants, the two or more exposure sources can illuminate or scan the master composite one after the other without the need to fix the photosensitive material between exposure steps.This is because the first photosensitive layer is insensitive to the wavelength range used to expose the second photosensitive layer and therefore does not need to be protected from it.

[0034] Due to the wavelength selectivity of the layers, holographic patterns of the second wavelength range, which are particularly reflected or diffracted by the second master hologram, are not accidentally exposed in the first light-sensitive layer. Instead, each master hologram can be replicated only in the designated light-sensitive layer(s). This prevents a mismatch between the color channels or the different wavelengths used to create the polychromatic hologram, so that the final polychromatic hologram is not off-color or distorted. Furthermore, patterns intended to be viewed only from a specific angle or under a specific wavelength of light do not appear from the wrong angle or in the wrong color. The resulting polychromatic hologram is therefore of particularly high quality.

[0035] Between the exposure of the first and second holograms, the need to attach movable mechanical components to the stationary replication assembly, such as rollers for applying new light-sensitive layers, is advantageously eliminated. The risk of introducing mechanical or optical defects is thus further reduced.

[0036] Additionally, holograms of different wavelength ranges, e.g., different colors, can be exposed in separate layers of the replication composite. This offers particularly high efficiency and quality compared to multiplex holograms exposed in the same layer. This can be attributed, at least in part, to the individual adaptation of each light-sensitive layer to the respective wavelength range, allowing sharp and efficient holograms to be created in each light-sensitive layer. This requirement cannot usually be met for all wavelength ranges used when non-wavelength-selective light-sensitive materials are used.

[0037] After exposure, the first and second replicated holograms preferably remain stationary in their layer structure in the replication composite.

[0038] Separate stacking and alignment of the different holograms to one another is not necessary. Furthermore, a step of mechanically and / or chemically bonding the first and second holograms to one another, for example by lamination or bonding, is preferably omitted. This represents a significant advantage compared to known prior art approaches to providing a hologram stack, in which finished holograms of different wavelength ranges must be positioned and stacked on top of one another, e.g., using positioning marks, to ensure alignment of the layers before pressure is applied to bond and / or laminate the layers. The mechanical distortions often introduced with these alignment and bonding steps are advantageously avoided.Highly efficient polychromatic holograms can thus be produced without compromising the alignment of the different holograms to each other.

[0039] The solution according to the invention thus combines the advantages of a multiplex hologram in terms of the lack of need for alignment of the individual holograms with each other with the advantages of the high efficiency of a polychromatic hologram stack.

[0040] For the purposes of the invention, a "method for replicating a hologram" or a "replication method" is preferably a method in which the diffraction pattern of an object, in particular a master hologram, is recorded in a light-sensitive material. This comprises at least one exposure of the respective master hologram, but may also include further preferred steps such as fixing, cutting, or trimming.

[0041] For the purposes of the invention, a "polychromatic hologram" is preferably a hologram configured to diffract electromagnetic radiation of different wavelengths, wherein the different wavelengths preferably differ by at least 50 nm, more preferably by at least 100 nm, and even more preferably by at least 200 nm. Preferably, the polychromatic hologram may comprise a plurality of channels, each channel corresponding to a different wavelength and / or wavelength range. Each channel may be the result of replicating a master hologram configured for the respective wavelength or wavelength range. For example, the channels may correspond to different colors, such as red, green, and blue light.For the purposes of the invention, a color preferably means light of a specific wavelength range from the visible spectrum (380 nm to 780 nm) with a bandwidth of less than 50 nm, preferably less than 40 nm, less than 30 nm, or less, with a maximum or peak at a central wavelength characteristic of the color. For blue light, for example, the central wavelength can be approximately 460 nm, while green light can have a central wavelength of approximately 530 nm, or red light a central wavelength of approximately 630 nm.

[0042] It may also be preferred for one or more of the channels to correspond to electromagnetic radiation outside the visible spectrum, such as UV radiation or IR radiation. The various channels can be present in a polychromatic hologram in the form of a diffraction structure configured to diffract electromagnetic radiation of the respective wavelength or wavelength range. A polychromatic hologram can generally be designed as a single-layer (as a multiplex) or multi-layer structure. Different diffraction structures can be present in a single layer of the light-sensitive material or in individual layers of a polychromatic hologram composite. The present invention describes in particular the production of multi-layer polychromatic holograms from multiplex or stacked master composites.In particular, a third or further hologram can be provided as a multiplex in one of the at least two light-sensitive layers of the replication composite. This means that the number of (master) holograms designed for different wavelength ranges in a polychromatic master composite or in the polychromatic hologram composite does not have to correspond to the number of light-sensitive layers in the same composite. Thus, several master holograms of the master composite can be replicated as a multiplex in one of the at least two light-sensitive layers of the replication composite. Alternatively, several master holograms can be present as a multiplex in one layer of the master composite and yet be replicated separately and without crosstalk in different light-sensitive layers of the replication composite to create a multilayer polychromatic hologram.

[0043] For the purposes of the invention, a "polychromatic hologram composite" is preferably a replication composite, wherein a hologram has been exposed in each of at least two light-sensitive layers. The at least two exposed holograms are designed for different wavelength ranges and are distributed between at least two different layers. Preferably, the light-sensitive layers were fixed to create the polychromatic hologram composite, so that a polychromatic hologram composite—in contrast to a replication composite with still light-sensitive layers—can no longer be exposed, and the polychromatic hologram composite can be used as a product for manipulating electromagnetic radiation. The terms "polychromatic hologram composite" and "multilayer polychromatic hologram" can be used synonymously here.

[0044] A "master hologram" within the meaning of the invention is preferably a holographic-optical element comprising at least one hologram to be replicated. The master hologram is designed for an optical function (e.g., diffraction, reflection, transmission, and / or refraction) for one or a plurality of wavelengths within a wavelength range. The master hologram can, for example, be a microstructure in the volume of a material in the form of a local difference in the refractive index. Such a master hologram is considered a so-called "volume hologram." The light transmitted by the master hologram can be converted into almost any desired distribution through diffraction and subsequent propagation. This can be an image, a logo, text, a light refraction pattern, or the like.In addition, the master hologram can be a technical hologram, such as a Bragg mirror, a diffuser or a hologram acting as a lens.

[0045] A "wavelength selectivity" of a master hologram "for a wavelength range" preferably means that the diffraction structure is configured for the diffraction of electromagnetic radiation with at least one wavelength in the wavelength range. Wavelength selectivity means, in particular, that the diffraction conditions are preferably only provided by the first master hologram for radiation within a first wavelength range. Radiation of other wavelengths is preferably not diffracted by the first master hologram. This preferably means that a spectral profile of the radiation reflected or diffracted by the first master hologram has an efficiency peak in the first wavelength range and no efficiency peaks outside the first wavelength range.Preferably, the efficiency peak in the first wavelength range has a maximum efficiency of at least 0.6, in particular at least 0.7, even more preferably at least 0.8, wherein the efficiency represents a relationship between the incident radiation and the radiation reflected or diffracted by the first master hologram. Even more preferably, the spectral profile of the radiation reflected or diffracted by the first master hologram outside the first wavelength range exhibits an efficiency of less than 0.2, preferably less than 0.1, particularly preferably zero or negligible. The same also applies to a wavelength selectivity of the second master hologram, according to which diffraction should occur selectively for light of at least one wavelength in the second wavelength range.

[0046] According to the invention, the first and second wavelength ranges are not identical. In preferred embodiments, the first and second wavelength ranges may represent disjoint ranges and have essentially no intersections. This may be the case, for example, if the first and second wavelength ranges correspond to different colors. For example, a first wavelength range may correspond to one color (e.g., blue, red, or green), while the second wavelength range corresponds to another color.

[0047] For the purposes of the invention, a "wavelength range" can be narrowband and comprise radiation of a characteristic target wavelength, for example, the characteristic wavelength emitted by a monochromatic laser. Preferably, the wavelength range has a bandwidth of less than 60 nm, preferably less than 50 nm, preferably less than 40 nm, less than 30 nm, or less, with a maximum or peak at a wavelength characteristic of the exposure source.

[0048] In the case of a reflection hologram, the hologram can be configured such that electromagnetic rays in the relevant wavelength range are diffracted, so that a first-order diffracted beam travels back into a replication compound. The first-order diffracted beam can interfere with the reference beam in the replication compound. Radiation with wavelengths outside the wavelength range can preferably be transmitted without diffraction. This preferably means that radiation with wavelengths outside the relevant wavelength range is transmitted with a percentage transmission of at least 80%, in particular at least 90%. In the case of a transmission hologram, the hologram can be configured such that electromagnetic rays in the relevant wavelength range are diffracted, so that a diffracted beam interferes with a reference beam in the replication compound.Electromagnetic radiation with wavelengths outside the relevant wavelength range can preferably be transmitted undiffracted. The master hologram therefore preferably only diffracts radiation of the wavelength for which it is designed.

[0049] A "light-sensitive layer" within the meaning of the invention is preferably a layer comprising a material that reacts to radiation from a region of the electromagnetic spectrum, with which the master composite is exposed. The light-sensitive material preferably reacts to light from the visible region of the electromagnetic spectrum. Particularly preferably, the light-sensitive material reacts to the radiation by generating a local change in its refractive index. This can occur, for example, through local polymerization of monomers or shorter polymer chains, as in a photopolymer.

[0050] A light-sensitive layer sensitive to radiation of a specific wavelength range preferably has, in the unexposed state, a minimum transmission of <90% for radiation of the specific wavelength range. Particularly preferably, the minimum transmission of the light-sensitive layer for radiation of the relevant wavelength range (the "desired wavelength range") with which a hologram is to be exposed in the light-sensitive layer is less than 85%, preferably less than 80%, more preferably less than 70%, more preferably less than 60%, more preferably less than 50%, more preferably less than 40%, and even more preferably less than 30%. At the same time, the light-sensitive layer should react to the radiation of the desired wavelength range, in particular by polymerization.In some preferred embodiments of the invention, the above-mentioned transmission values ​​refer to the average (rather than the minimum) percentage transmission over the respective wavelength range. In further preferred embodiments of the invention, the light-sensitive layer has a reduced transmission across the entire specific wavelength range, for example, due to a broad transmission trough. In this case, the aforementioned transmission values ​​can also be considered limit values ​​for the maximum percentage transmission in the specific wavelength range.

[0051] Preferably, the light-sensitive layer is insensitive to radiation in all other wavelength ranges ("undesired wavelength ranges"), meaning that the light-sensitive layer preferably experiences essentially no reaction to radiation outside the desired wavelength range. The light-sensitive layer is particularly preferably insensitive to radiation in the wavelength ranges to which further layers of the replication composite are exposed. Particularly preferably, the light-sensitive layer has a high transmission for radiation in undesired wavelength ranges, in particular for wavelength ranges to which further layers of the replication composite are exposed.The high transmission is preferably at least 40%, more preferably at least 50%, more preferably at least 60%, more preferably at least 70%, more preferably at least 80%, more preferably at least 85%, more preferably at least 90% and particularly preferably at least 95%.

[0052] A "replication composite" within the meaning of the invention is preferably a multilayer material comprising at least two photosensitive layers. The photosensitive layers preferably comprise a photosensitive material, such as a silver halide, a dichroic gelatin, a photoresist, a photopolymer, a photochromic material, a photothermoplastic, a synthetic salt (e.g., LiNbOa), a solid inorganic compound (e.g., BiiaSiOao), or combinations thereof, with photopolymers being particularly preferred. Each photosensitive layer is preferably sensitive to electromagnetic radiation in a limited wavelength range, in particular with little or no overlap between the wavelength ranges to which the photosensitive layers are sensitive.Any number of light-sensitive layers can be provided in a replication composite, for example two, three or more, whereby the sensitivities of the layers preferably do not overlap.

[0053] Preferably, the replication network comprises at least one replication substrate.

[0054] For the purposes of the invention, a "replication substrate" is preferably a component that mechanically stabilizes the one or more photosensitive layers of the replication composite. In preferred embodiments, the replication substrate can be located between the one or more photosensitive layers and the master composite and preferably mediates optical contact between the master composite and the photosensitive layers. Likewise, it can also be preferred for the replication substrate to be located on a side of the photosensitive layers facing away from the master composite, so that the photosensitive layers preferably directly contact the master composite. One or more replication substrates preferably protect the photosensitive layers from mechanical stress or damage.Preferably, the replication substrates are also insensitive to electromagnetic radiation used to expose and / or fix the holograms in the photosensitive layers. Such a replication substrate can also prevent the drying of the photosensitive layers and / or their reaction with air.

[0055] In a preferred embodiment of the invention, the replication substrate is a film-like layer, such as a carrier film or a flexible base. The replication substrate can be used for handling the photosensitive layers of the replication composite, e.g., to combine them into a master composite and integrate them into a final product. Furthermore, the replication substrate can protect a master composite from residues from photosensitive layers.

[0056] In a further preferred embodiment of the invention, the replication composite comprises at least two replication substrates, which are preferably present as two outer carrier films, wherein the carrier films are preferably transparent to electromagnetic radiation of all wavelengths with which the replication composite is to be irradiated and, in particular, exposed. Such carrier films can optionally carry, enclose, and / or separate successive photosensitive layers. The carrier films preferably protect the process components used, in particular the master composite, from unwanted residues that could be left behind by the photosensitive layers. Furthermore, the photosensitive layers or the holograms replicated therein are mechanically stabilized or protected.

[0057] In a further preferred embodiment of the invention, the replication substrate is rigid, with two or more photosensitive layers laminated to the replication substrate to create a stable replication composite. Such a replication composite can be provided as a discrete unit (instead of a roll or web) comprising a rigid replication substrate supporting a stack of at least two photosensitive layers. Such a rigid replication substrate can have similar properties to a master substrate. An advantage of this embodiment is that a rigid replication substrate can be transported with the remaining parts of the replication composite to further processing stations of a manufacturing process.For example, a rigid replication substrate can be used to precisely position multiple multilayer polychromatic holograms—after exposure—on top of each other with mechanical precision and encapsulate them between the substrates. This way, only the rigid replication substrates need to be aligned on top of each other, which is much more precise and manageable than aligning foil-like materials. A six-layer polychromatic hologram, which functions as a combination of concave and planar mirrors, as described in DE102021116146A1, can be precisely manufactured in this way. For example, two polychromatic hologram composites, each comprising RGB layers, can be positioned on top of each other by adjusting their rigid replication substrates so that alignment is achieved by an alignment mark or similar.Not only is this easier than aligning and overlaying flexible films, but it only needs to be done once for the six-layer hologram.

[0058] A rigid replication substrate is preferably provided individually for each polychromatic hologram. In some applications, the rigid replication substrate can form part of the final product, e.g., as a base for incorporating the polychromatic hologram into a final product. This is particularly advantageous when multiple polychromatic holograms are to be stacked on top of each other in a precise relative position. The use of rigid replication substrates for the various polychromatic holograms offers an alternative to roll-based stacking methods, which can result in deformation of the replication composites. The replication substrates can include positioning markers.These can be used, for example, to precisely position two multilayer polychromatic holograms on top of each other, encapsulating them between the two replication substrates with the respective positioning marks aligned. Preferably, the exposed and preferably fixed multilayer polychromatic hologram is delaminated from the rigid replication substrate to obtain a flexible polychromatic hologram. The rigid replication substrate can then be reused.

[0059] In a preferred embodiment of the invention, the replication composite is present as a composite web.

[0060] A "composite web" within the meaning of the invention is preferably a composite material, in particular a replication composite, with a length that is at least twice, preferably at least five times, and more preferably at least twenty times its width. The thickness of the composite web is preferably adjusted to have a certain flexibility so that it can be provided, for example, as a roll. Preferably, the composite web has a thickness of up to 1500 μm, preferably up to 1000 μm, more preferably up to 700 μm. The composite web comprises at least two layers of a photosensitive material. The composite web preferably also comprises a replication substrate as a carrier film. Preferably, the composite web encloses one or more layers of the photosensitive material between two transparent carrier films that have a similar refractive index to the photosensitive material.The refractive index of the carrier films and the light-sensitive material is preferably between 1.4 and 1.6. The light-sensitive material can be, for example, a light-sensitive photopolymer or a dichroic gelatin. The light-sensitive material is preferably wavelength-selective.

[0061] The replication composite provided as a composite web can be film-like and delivered as a roll. The replication composite is preferably provided with protective films on one or both sides prior to exposure to protect the replication substrate and / or the light-sensitive layers. The protective film preferably protects the replication composite from scratches or mechanical damage. One or both protective films are preferably removed prior to exposure of the light-sensitive layers so that the replication composite can be brought into direct contact with a master composite. In preferred embodiments of the invention, the replication composite is transported on a conveyor belt by means of transport rollers, with the replication process preferably taking place continuously.This embodiment may be particularly preferred if the replication composite is not provided in the form of a web-shaped composite web, but for example in the form of smaller, separate replication composites (sheets).

[0062] Once all light-sensitive layers of the replication composite have been processed, in particular by exposure and optionally fixation, so that they are essentially no longer light-sensitive, the product is preferably referred to as a "polychromatic hologram composite." A polychromatic hologram composite is therefore preferably a multilayer product resulting from the processing of all light-sensitive layers of the replication composite. The polychromatic hologram composite preferably comprises two or more (partial) holograms in two or more hologram layers, which are combined to form a composite. Optionally, the polychromatic hologram composite comprises further layers such as a replication substrate, in particular in the form of a carrier film.

[0063] In a preferred embodiment of the invention, the polychromatic hologram composite is provided with a protective film on one or both sides. This can be applied after exposure and / or fixation of all light-sensitive layers and advantageously protects the polychromatic hologram from mechanical damage. If the replication composite or the polychromatic hologram composite is provided with a protective film, this film preferably adheres more weakly to the layers of the replication composite or the polychromatic hologram composite (i.e., the light-sensitive layers or hologram layers, or optionally a replication substrate) than these layers adhere to each other.

[0064] In a preferred embodiment of the invention, the bond between the layers of the replication composite or the multilayer polychromatic hologram is such that they cannot be separated from one another by the application of even slight force and are therefore essentially permanently bonded to one another. The peel force between the layers of the replication composite or the multilayer polychromatic hologram is preferably at least 10 N / cm, more preferably at least 50 N / cm, and even more preferably at least 100 N / cm.

[0065] In a preferred embodiment of the invention, the bond between a protective film and an outer layer (in particular a light-sensitive layer, hologram layer, or replication substrate) of the replication composite or the multilayer polychromatic hologram is such that it can be removed from the composite by applying a slight force. Preferably, the peel force required to remove the protective film from the replication composite or the polychromatic hologram composite is no more than 3 N / cm, preferably no more than 1 N / cm, even more preferably no more than 0.2 N / cm, and particularly preferably no more than 0.1 N / cm.

[0066] A "master composite" within the meaning of the invention is preferably a multilayer composite comprising at least one master hologram layer and a master substrate. The at least one master hologram layer comprises the first master hologram. The second master hologram is present either in the same master hologram layer as a multiplex or in a further master hologram layer of the master composite. The master composite preferably comprises at least a first master hologram and a second master hologram in a layered structure. The master composite can preferably comprise further layers, such as one or more covers and / or a master substrate, so that the master hologram (or master holograms) are preferably present between the master substrate and the cover. The master holograms are preferably laminated to a surface of the master substrate.Preferably, all layers of the master composite are firmly bonded to one another so that they can only be separated from one another with a peel force of at least 10 N / cm, preferably at least 50 N / cm, more preferably at least 100 N / cm.

[0067] The master composite is preferably rigid. A rigid master composite is preferably not designed as a film. However, the rigidity of the master composite can be ensured by the master substrate. In particular, a rigid master composite has a thickness preferably greater than 1 mm, more preferably greater than 5 mm, and even more preferably greater than 1 cm.

[0068] A structure, a material or a composite material is considered rigid within the meaning of the invention if it has a modulus of elasticity of at least 5 GPa, preferably of at least 50 GPa, particularly preferably of at least 100 GPa.

[0069] The "master substrate" is preferably a three-dimensional unit comprising a master hologram in a shape that facilitates its handling and mobility. The master hologram is, in particular, connected to the master substrate in a fixed position such that a movement of the master substrate directly leads to a corresponding movement of the master hologram. The dimensions of the master substrate are preferably larger than those of the master hologram in all directions. The master substrate preferably has a length and width that at least corresponds to that of the master hologram; it may also be preferred that one length and / or width of the master substrate is slightly larger than one length and / or width of the master holograms it supports, for example by less than 30%, preferably less than 20%, 10%, or less.Preferably, the master substrate is at least twice, preferably five times and particularly preferably at least twenty times as high as the master hologram.

[0070] The master substrate can preferably be in the form of a cuboid block, a plate, a prism, or a roller. At least one surface of the master substrate is preferably arranged parallel to the master holograms. By attaching the first and second master holograms to or integrating them into the master substrate, they are robustly fixed and mechanically stabilized within the master composite.

[0071] In a preferred embodiment of the invention, the master composite comprises any number of further substrates, which are preferably configured for the mechanical support of the master holograms.

[0072] The master substrate is preferably made of a material that is transparent for exposure, preferably of an optical glass or plastic.

[0073] Preferably, the master substrate can be formed from a material that is an optical plastic, preferably selected from the group comprising: polymethyl methacrylate (PMMA), polycarbonate (PC), cycloolefin polymers (COP), and cycloolefin copolymers (COC), and / or an optical glass, preferably selected from the group comprising: borosilicate glass, quartz glass, B270, N-BK7, N-SF2, P-SF68, P-SK57Q1, P-SK58A, and P-BK7. The master substrate preferably has a refractive index between 1.4 and 1.6.

[0074] The master holograms can be laminated to a surface of the master substrate to create a master composite. The master substrate is preferably configured to support the layered structure of the first and second master holograms, and optionally third or further master holograms. Preferably, the first and second master holograms are laminated to a surface of the master substrate to create the layered structure. The master substrate is preferably rigid and transparent to the first and second wavelength ranges. In some preferred embodiments, the master composite may further comprise a transparent top cover for protecting one or both master holograms, which is / are present between the cover and the master substrate. Preferably, the top cover is also transparent. The top cover may, for example, be a transparent film or a glass layer.The top cover may also have a coating, in particular a primer coating or an adhesive layer. The coating may be configured to increase adhesion to the replication composite.

[0075] For the purposes of the invention, the term "transparent" or "transparency" preferably refers to a property of a material whereby it is substantially permeable to light. Preferably, a transparent material for the purposes of the invention is transmissive for at least part of the electromagnetic spectrum, preferably with wavelengths between 200 nm - 25 pm, more preferably between 400 nm - 780 nm, even more preferably between 430 nm - 750 nm. Such a material can be provided with UV-absorbing additives which improve the aging resistance of the material, while the material remains transparent for substantially the entire visible range of the electromagnetic spectrum. A material is preferably considered transparent for a wavelength range if it essentially completely transmits radiation of all wavelengths in the relevant wavelength range.The percentage transmission is preferably at least 80%, more preferably at least 85%, even more preferably at least 90%, and particularly preferably at least 95% across the entire wavelength range. A material is preferably considered transparent for a portion of the electromagnetic spectrum if it is substantially transmissive in this portion and exhibits no absorption peaks. An absorption peak in this sense preferably corresponds to a transmission of less than 80%, in particular less than 70%, less than 60%, 50%, 40%, 30%, or less. A transparent material, for example a transparent master substrate or a transparent cover, is particularly preferably permeable to light of a wavelength range with which exposure of the master holograms takes place. A transparent material can also be colored in such a way that it selects the light radiation of one or more specific wavelengths.

[0076] It is preferred that the surface or cover of the master composite comprises glass, PC, TAC, or PMMA. The surface material can be in the form of a film or plate to protect the master hologram. However, the surface or cover material can also be the material of the master substrate itself and, for example, have a cuboid or cylindrical shape.

[0077] In the context of the invention, "exposure" is preferably understood to mean the targeted directing of electromagnetic radiation onto a correspondingly sensitive surface, preferably to form a hologram. Various methods for exposing a hologram are known, including transmissive or reflective techniques for producing volume holograms.

[0078] A "volume hologram" is preferably written into a sensitive layer by the interference of two light beams (a so-called reference beam and an object beam). A volume hologram is preferably written into the replication composite. This can preferably be done using a transmission or reflection technique. The interference of object and reference beams within the hologram volume preferably creates a sequence of Bragg planes. A volume hologram therefore preferably has a non-negligible extension in the propagation direction of the light beams, whereby the Bragg condition applies to the reconstruction of a volume hologram.

[0079] For this reason, volume holograms exhibit wavelength and / or angle selectivity. For the recording of full-color polychromatic volume holograms, exposure sources can be used that emit, for example, the three primary colors blue, green, and red. The three beams preferably simultaneously expose a portion of the replication array at the same angle. The multiple light-sensitive layers of the replication array can each store at least one volume hologram. For example, the first light-sensitive layer can store a red volume hologram, while the second light-sensitive layer stores a green-blue multiplex volume hologram. The second light-sensitive layer would thus have two volume holograms. Alternatively, red, blue, and green volume holograms can each be exposed in a separate light-sensitive layer.Other combinations are also conceivable, such as a red-green multiplex in a first layer and a blue hologram in a second layer, an RGB multiplex in a first layer and a UV hologram in a second layer, etc. The volume holograms that form the polychromatic hologram can be referred to as "partial holograms." To reproduce the polychromatic hologram, one can exploit the fact that each partial hologram can be reconstructed using only the color with which it was recorded. Thus, the three reconstructed color separations superimpose themselves to form a color, true-to-original image, provided the color components are correctly weighted.

[0080] Exposure can preferably be carried out by an exposure module which has one or more exposure sources provided for this purpose. The exposure source(s) (also "light sources" within the meaning of the invention) preferably emit electromagnetic radiation in a first and / or second wavelength range for this purpose. The emitted electromagnetic radiation can comprise visible light or radiation with wavelengths outside the visible range of the electromagnetic spectrum. Preferably, a coherent light beam is emitted by the exposure source. Coherence preferably refers to the property of optical waves according to which there is a fixed phase relationship between two wave trains. As a result of the fixed phase relationship between the two wave trains, spatially stable interference patterns can arise. With regard to coherence, a distinction can be made between temporal and spatial coherence.Spatial coherence preferably represents a measure of a fixed phase relationship between wave trains perpendicular to the propagation direction and is present, for example, for parallel light beams. Temporal coherence preferably represents a fixed phase relationship between wave trains along the propagation direction and is present in particular for narrowband, preferably monochromatic light beams.

[0081] The coherence length preferably refers to the maximum path length or travel time difference between two electromagnetic beams from a starting point, so that a (spatially and temporally) stable interference pattern is still created when they superpose. The coherence time preferably refers to the time required for the radiation to travel one coherence length.

[0082] In a preferred embodiment of the invention, the exposure of the master composite comprising the first and second master holograms takes place in one exposure process, preferably simultaneously. This contrasts with known methods for producing multilayer polychromatic holograms, in which exposure typically takes place in different exposure processes, whereby the different exposure processes take place independently of one another on different replication composites and, in particular, require a fixing step after each individual exposure process in order to avoid quality defects due to stray light. The implementation of multiple fixing steps can be avoided in the present invention by exposing the different light-sensitive layers simultaneously or immediately one after the other. Fixing between exposure steps is also unnecessary due to the wavelength selectivity.

[0083] For the purposes of the invention, "an exposure process" is an exposure method that is not interrupted by steps designed to influence the chemical or physical properties of the photosensitive layers of the replication composite. In particular, the replication composite is preferably not subjected to any opto- or thermochemical steps between the exposure steps, in particular no steps of curing, drying, pre-fixing, or fixing. The replication composite preferably also remains at the same process station, in particular it remains in optical contact with the master composite for the duration of the exposure. In this way, the exposure can be considered a single process, even if one or more exposure sources are used and even if one or more of the exposure sources are temporarily switched off or directed away from the master composite during the individual exposure process.

[0084] For the purposes of the invention, "simultaneous" exposure refers to the direction of one or more exposure sources onto the master composite for the simultaneous exposure of the first and second master holograms in order to replicate them in the replication composite, wherein the one or more exposure sources emit radiation of the first and second wavelength ranges. The simultaneous exposure preferably comprises a temporally overlapping scanning of the master holograms by different exposure sources that emit radiation of the first and second wavelength ranges. Furthermore, the simultaneous exposure preferably comprises the simultaneous or temporally overlapping direction of radiation of the first and second wavelength ranges from different angles onto the first and second master holograms, such that the first and second replicated holograms can be reconstructed from different angles.

[0085] In a preferred embodiment of the invention, the master composite comprises a third master hologram. The third master hologram is present, in particular, in a layered structure with the first and second master holograms. The third master hologram is preferably wavelength-selective for a third wavelength range. The replication composite preferably comprises a third light-sensitive layer, wherein the third light-sensitive layer is sensitive to radiation in the third wavelength range, but not to radiation in the first or second wavelength range.

[0086] This allows a polychromatic hologram comprising three precisely aligned color channels to be created, for example, to display a full-color image. The advantage of this is that the replication composite does not need to be moved between the exposure steps of the first, second, and third holograms, thus eliminating alignment errors between the holograms.

[0087] For example, a laser system with three monochromatic lasers or a polychromatic laser with a laser emission in the red, green or blue (RGB) range can be provided for this purpose.

[0088] In an alternative preferred embodiment of the invention, the third master hologram is provided separately from the master composite of the first and second master holograms. The third master hologram can, for example, be provided in a further master composite, wherein the further master composite preferably comprises a further master substrate, such as a glass plate. The further master composite can optionally comprise further master holograms, such as a fourth, fifth, and further master holograms. The further master composite can be provided at a downstream exposure station.In this embodiment, the alignment of the various holograms in the respective layers of the replication composite is also improved compared to the prior art, since the master holograms are at least partially bundled in master composites and at least some of the master holograms are exposed in a single exposure station. This eliminates at least one alignment step.

[0089] In a further preferred embodiment of the invention, one of the first, second or third wavelength ranges corresponds to red light, wherein the wavelength range is preferably between 590 - 750 nm, particularly preferably between 620 - 700 nm. Preferably, one of the first, second or third wavelength ranges corresponds to green light, wherein the wavelength range is preferably between 490 - 590 nm, particularly preferably between 500

[0090] - 560 nm. Preferably, one of the first, second or third wavelength ranges corresponds to blue light, wherein the wavelength range is preferably between 380

[0091] - 490 nm, particularly preferably between 420 - 475 nm.

[0092] In this way, a polychromatic RGB (red-green-blue) hologram can be created. Such a hologram can diffract light from essentially the entire visible spectrum, producing full-color holographic images with a high degree of sharpness. Such images can achieve very high visual quality due to the precise alignment of the channels. The polychromatic RGB hologram can also redirect light from various regions of the visible spectrum in a compact manner, which is particularly useful for HOEs integrated into car, aircraft, or other vehicle windows.

[0093] In a further preferred embodiment of the invention, the exposure of the replication composite is carried out by at least a first and a second exposure source, wherein the first exposure source emits radiation with a wavelength in the first wavelength range and the second exposure source emits radiation with a wavelength in the second wavelength range and / or wherein the exposure is carried out by at least one polychromatic exposure source, wherein the polychromatic exposure source emits radiation with a wavelength in the first wavelength range and the second wavelength range.The use of multiple exposure sources is particularly advantageous because it allows the various master holograms of the master composite to be replicated simultaneously or in rapid succession into different layers of the replication composite, while also providing the freedom to direct the radiation of the different wavelength ranges at different angles. This allows, for example, security elements to be created that display different patterns or information depending on the angle of inclination or viewing. For example, different images can be applied to a specific location in the replication composite, so that the different images are visible in different colors when a card is tilted. The alternative of using a polychromatic and / or broadband exposure source makes it possible to expose all light-sensitive layers of the replication composite simultaneously. This ensures a very fast replication process.

[0094] In a further preferred embodiment of the invention, at least one laser and / or one light-emitting diode (LED), for example a scanning RGB laser, is used for the exposure. Such an exposure source can provide coherent, collimated radiation directed at a precise angle onto the master hologram. At the same time, the radiation can have one or more specific, narrow wavelength peaks. It can be advantageous for the exposure source to have one or more characteristic wavelengths defined by peaks in its emission spectrum. A peak preferably corresponds to a central wavelength characteristic of a color (or non-visible radiation). For blue light, for example, the central wavelength can be approximately 460 nm, while green light can have a central wavelength of approximately 530 nm, or red light a central wavelength of approximately 640 nm.

[0095] Since the wavelength ranges emitted by the lasers or LEDs are narrow (e.g. with a bandwidth of <30 nm for LEDs and significantly lower for lasers), unwanted crosstalk between the different photosensitive layers can be effectively avoided. This is particularly advantageous when the photosensitive layers have broad-band absorption (or sensitivity) peaks. Such absorption peaks can, for example, have a full width at half maximum (FWHM) of at least 30 nm. This occurs, for example, when the dye used in the first photosensitive layer has a broad absorption peak with gently tapered edges. The relevant absorption peak of such a dye could overlap with the tapered edges of an absorption peak of a different dye in a different photosensitive layer.This overlap does not lead to crosstalk if the wavelength peaks of the exposure source(s) used are sufficiently narrow and sufficiently spaced from one another. In preferred embodiments, the exposure source comprises a laser. Particularly preferably, it is a narrow-band, preferably monochromatic laser with a preferred wavelength in the visible range (preferably 400 nm to 780 nm), wherein the emitted radiation preferably falls within a wavelength range to which a light-sensitive layer of the replication composite is sensitive. Non-exhaustive examples include solid-state lasers, preferably semiconductor lasers or laser diodes, gas lasers, or dye lasers. Lasers can be selected to emit radiation of a specific wavelength or wavelength range. This can be achieved by selecting a laser made of a suitable material.For example, ruby ​​lasers, He-Ne lasers, Ar. + -laser, Kr^-laser, He-Cd-laser and / or Nd 3+ YAG lasers can be used. These or other laser types can be combined with an optical parametric oscillator to generate coherent beams of different wavelengths. Lasers with different characteristic wavelengths can also be combined, for example, to create an RG B laser.

[0096] Various laser types, particularly solid-state lasers, can be combined with an optical parametric oscillator to generate coherent beams of different wavelengths as a tunable system. The optical parametric oscillator preferably comprises an optical resonator and at least one nonlinear optical crystal. Systems with a plurality of converter crystals can be used, in particular, using three-wave mixing (f_pumpe = f_signal + f_dler). By varying the frequency of f_signal and / or f_dler, laser wavelengths can be generated in a very broad wavelength range. This includes, in particular, the entire visible and infrared ranges of the electromagnetic spectrum.

[0097] Other illumination sources, preferably coherent illumination sources, can also be used. Narrowband illumination sources, preferably monochromatic illumination sources, such as light-emitting diodes (LEDs), optionally in combination with monochromators, are preferred.

[0098] For replication with different wavelengths, in particular a first and second wavelength range, it is preferred to provide an exposure source whose emitted radiation falls within the respective different wavelength ranges. The wavelength-selecting component(s) of the photosensitive layer can also be selected to precisely match the wavelength peaks of the exposure source. The wavelength range to which the photosensitive layer in question is sensitive preferably encompasses or overlaps the wavelength range of the radiation emitted by the exposure source. It is particularly preferred that the wavelength range to which the photosensitive layer is sensitive is broader than the wavelength range emitted by the exposure source, so that the latter is completely encompassed by the former.In this way, the photosensitive layer is sensitive to essentially all the radiation reaching it from the exposure source, which increases the efficiency of the process.

[0099] The exposure source can be monochromatic. This preferably means that the emitted radiation is narrowband, for example, with a bandwidth of less than 60 nm, preferably less than 50 nm, even more preferably less than 40 nm, and most preferably less than 30 nm.

[0100] The exposure source can also be polychromatic and / or white. A polychromatic exposure source preferably comprises two or more monochromatic exposure sources or has more than one intensity peak in the radiation emitted by it. If the polychromatic exposure source comprises several monochromatic exposure sources, these are preferably arranged as a unit so that they have the same exposure angle, move together and / or scan a surface simultaneously. However, the intensity of each monochromatic exposure source can be individually modulated. For the purposes of the invention, 'white' preferably means light with components of at least three or more colors, preferably with components in the blue, green and red range or with components in the magenta, cyan and yellow range. The components of a polychromatic hologram of a specific wavelength range orFor the purposes of the invention, color or color combinations can also be referred to as a color channel. A red color channel therefore preferably refers to a portion of a holographic image in the red color range, while a white color channel preferably refers to a portion of the holographic image of a combination of a red, blue, and green color range.

[0101] Preferably, the light-sensitive layers of the replication composite comprise a photopolymer composition. Such compositions have proven to be particularly versatile and compatible with many additives and dyes, allowing their sensitivity to be adjusted to different wavelength ranges of the electromagnetic spectrum. At the same time, photopolymers have been found to produce particularly efficient volume holograms.

[0102] In a preferred embodiment of the invention, a photopolymer composition of a photosensitive layer comprises the following basic components: a writing monomer (also referred to as "photoactive monomer") and / or a writing oligomer, which is preferably configured to undergo a polymerization reaction to form a photopolymer, a wavelength-selective photoinitiator system, which is preferably configured to trigger polymerization of the photoactive monomer and / or oligomer upon exposure, and a polymer matrix and / or one or more precursors for forming the polymer matrix (in particular matrix monomers), which are preferably substantially inert to the exposure radiation.

[0103] Preferably, the photopolymer and the polymer matrix have different refractive indices, the difference between their refractive indices preferably being at least 0.001, in particular at least 0.003, even more preferably at least 0.02.

[0104] A writing monomer or writing oligomer is preferably a chemical compound configured to react when the photopolymer composition is exposed to radiation to form polymer chains. The formation of polymer chains preferably involves an increase in chain length when the photopolymer composition is exposed to radiation. The writing monomers or writing oligomers of the photopolymer composition may be of the same or different types and may optionally be configured to copolymerize. The polymerization reaction of the writing monomers or writing oligomers may be triggered by other physical or chemical reactions in the photopolymer composition, these reactions preferably being driven by the presence or intensity of electromagnetic radiation.

[0105] In a preferred embodiment of the invention, the writing monomer and / or the writing oligomer comprises one or more functional groups selected from the following group: cyclic carbonates, cyclic esters, dioxalanes, maleyl groups, fumaryl groups, maleimide groups, dicyclopentadienyl groups, acrylamides, methacrylamides, vinyl esters, vinyl ethers, vinylcarbazoles, other vinyl derivatives, and ethylenic unsaturation (i.e., a double bond), particularly acrylates and methacrylates. For example, the photoactive monomer can be a methyl methacrylate, with the double bond acting as a functional group. Alternatively or additionally, the photoactive monomers can comprise two or more copolymers. The photoactive monomer and / or the photoactive oligomer are preferably present in the composition at a concentration of 1-90 mass percent, particularly preferably 10-60 mass percent.

[0106] The polymer matrix is ​​preferably a polymeric material in which the writing monomers and / or writing oligomers are embedded in such a way that their reaction is not hindered upon exposure to radiation. Preferably, the writing monomers and / or writing oligomers can diffuse within the uncured polymer matrix by Brownian motion. Preferably, the polymer matrix does not react when the photopolymer composition is exposed to the exposure radiation. Once the photopolymerization of the writing monomer and / or writing oligomer is complete, the polymerized structures resulting from the reaction of the writing monomer and / or writing oligomer preferably have a different refractive index than the polymer matrix. The polymer matrix can preferably be configured to be chemically stabilized by the application of radiation and / or heat.

[0107] In a preferred embodiment of the invention, the polymer matrix is ​​selected from the following group: poly(vinyl acetate), poly(styrene), poly(ethylene), poly(propylene), poly(ethylene oxide), linear polyamides, linear polyesters, linear polycarbonates, linear polyurethanes, poly(vinyl chloride), poly(vinyl alcohol-co-vinyl acetate), poly-, diacrylates or dimethacrylates, in particular urethane acrylates and urethane methacrylates, and combinations thereof. Those skilled in the art will know which precursors to select to form such a polymer matrix. The proportion of the polymer matrix or its precursor substances in the composition is preferably between 10 and 95 percent by mass, particularly preferably between 20 and 60 percent by mass.

[0108] A wavelength-selective photoinitiator system is preferably a combination of two or more chemical components in a composition, wherein at least one chemical component reacts to electromagnetic radiation of the desired wavelength range upon exposure to initiate photopolymerization. The photoinitiator system can be considered unstable in the presence of light or other electromagnetic radiation. The instability of the photoinitiator system preferably triggers one or more additional reactions in the photopolymer composition, which in particular lead to the polymerization of the writing monomer or writing oligomer.

[0109] In a preferred embodiment of the invention, the wavelength-selective photoinitiator system comprises wavelength-selective photoinitiator, wherein the wavelength-selective photoinitiator preferably triggers a polymerization reaction of the photoactive monomer and / or oligomer upon absorption of electromagnetic exposure radiation of a desired wavelength range.

[0110] In a further preferred embodiment of the invention, the wavelength-selective photoinitiator system comprises a dye and a co-photoinitiator, wherein the co-photoinitiator preferably triggers a polymerization reaction of the photoactive monomer and / or oligomer upon absorption of electromagnetic exposure radiation of a desired wavelength range by the dye. Without wishing to be limited to any theory, in embodiments this can be attributed to a decomposition of the co-photoinitiator after activation by the dye. Such decomposition can, for example, release a radical that triggers the polymerization of the monomer or oligomer. Alternative reaction mechanisms are of course not excluded.Preferably, the wavelength-selective photoinitiator system further comprises a photoinitiator or a combination of a UV-absorbing dye and a co-photoinitiator for fixing the photopolymer composition. Preferably, the wavelength-selective photoinitiator system comprises at least one further chemical component that reacts to electromagnetic radiation for fixing the photopolymer composition. The at least one further chemical component is preferably substantially insensitive to the electromagnetic radiation of the desired wavelength range for exposure, so that it is preferably only activated during a fixing step.

[0111] Optionally, the wavelength-selective photoinitiator system additionally comprises one or more catalysts.

[0112] The type and amount of components of the photoinitiator system can be selected by the skilled person, among other things, based on whether radical polymerization of the writing monomers or oligomers, cationic polymerization, anionic polymerization of the writing monomers or oligomers, or a combination of these polymerization mechanisms is intended. The selection of the desired polymerization mechanism may depend on the optical and chemical properties of the photopolymer as well as the required exposure speed. On this basis, the skilled person can select suitable components for the wavelength-selective photoinitiator system.

[0113] As an example, one of the following photoinitiators can be used in the photoinitiator system: bis(q-5-2,4-cyclopentadien-1-yl)bis[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl]titanium (commercially available as Irgacure 784), 5,7-diiodo-3-butoxy-6-fluorone (commercially available as H-Nu 470), 1-[4-(phenylthio)phenyl]-1,2-octanedione 2-(O-benzoyloxime) (commercially available as Irgacure OXE01), 1-[({1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]ethylidene}amino)oxy]ethanone (commercially available as Irgacure OXE02). For a cationic polymerization, for example, (q5-2,4-cyclopentadien-1-yl)(q6-isopropylbenzene) iron(II) hexafluorophosphate (commercially available as Irgacure 261), a diazonium salt, an organometallic complex or an onium salt, in particular a sulfonium salt or an iodonium salt, can be used.

[0114] The photoinitiator is preferably present in the composition in an amount of 0.01 - 30 volume percent, particularly preferably 0.5 - 10 volume percent.

[0115] For the purposes of the invention, a "dye" is preferably a substance which has a high absorption in a desired wavelength range for the exposure of a photosensitive layer. The dye preferably acts as a photochemical "catalyst", in particular by transferring light energy to one or more other components of a photosensitive composition, wherein the other component(s) optionally have other absorption properties. In a particularly preferred embodiment, the dye absorbs electromagnetic exposure radiation of the desired wavelength range and enters an excited state which causes it to react with a co-photoinitiator. The co-photoinitiator preferably triggers photopolymerization.The dye can thus adjust the absorption spectrum of a light-sensitive layer and its reactivity to radiation of a specific wavelength range, even if the other reacting components (in particular writing monomers or oligomers) are generic.

[0116] It should be noted that the term "dye" within the meaning of the invention also includes pigments and other colored molecules that are suitable for use as photosensitizers and are not necessarily chemically classified as dyes.

[0117] In preferred embodiments, the dye may be selected from one of the following groups: cyanines, isocyanines, indocarbocyanine(s), xanthene dyes (e.g.Fuorescein), phencarboxonium, indamine dyes, ketones, a-diketones, substituted benzophenones, substituted camphorquinones, substituted thioxanthones, substituted related amino (or thiol) derivatives, substituted thioxanthone fluorenes, anthraquinones, fluorenones, flavones, anthrones, quinones, naphthacenequinones, quinolines, benzodioxinones, thiazines, phenothiazines, acridines, N-methylacridones, phenosafranines, thiopyronines, riboflavins, phenoxazines, pyrromethenes, polymethines, fluorones, squaryls, julolidine dyes, phenoxazones, quinolinones, phthalocyanines, benzopyranones, rhodanines, crystal violet / benzofuranone derivatives, Dimethylaminostyryl benzothiazolinium iodides, diarylmethine dyes, triarylmethine dyes, triphenylmethane dyes, bis-arylimidazole derivatives, coumarin derivatives, ketocoumarin derivatives, pyrylium salts, thiopyrylium salts, hydroxam esters and thiohydroxam esters.

[0118] In preferred embodiments, the co-photoinitiator can be selected from one of the following groups: organic amines, preferably amine-functionalized acrylates, tertiary amines, such as N,N-dimethyl-2,6-diisopropylaniline, or phenylglycine derivatives, such as N-phenylglycine or N-phenylglycine ethyl ester, thiols, for example 2-mercaptobenzimidazoles or 2-mercaptobenzthiazole and borate salts, preferably triarylalkyl borates, such as tetrabutylammonium tetrahexylborate, tetrabutylammonium triphenylhexylborate, tetrabutylammonium tris-(3-fluorophenyl)-hexylborate or tetrabutylammonium tris-(3-chloro-4-methylphenyl)-hexylborate.

[0119] The co-photoinitiator is preferably present in the composition in an amount of 0.01 - 30 volume percent, particularly preferably 0.5 - 10 volume percent.

[0120] In a preferred embodiment of the invention, the first and second photosensitive layers of the replication composite comprise a different photopolymer composition, wherein the photopolymer compositions differ in the wavelength selectivity of the wavelength-selective photoinitiator system, in particular the type and amount of wavelength-selective photoinitiators, dyes and / or co-photoinitiators present.

[0121] In a preferred embodiment of the invention, the photopolymer composition of a photosensitive layer comprises a dye configured to absorb radiation having a wavelength within the desired range of the electromagnetic spectrum. Preferably, the dye is present as part of a multicomponent photoinitiator system. In a further preferred embodiment of the invention, the first photosensitive layer of the replication composite comprises a different photopolymer composition than the second photosensitive layer of the same replication composite. If the replication composite comprises further photosensitive layers for exposure to other wavelength ranges, these layers preferably also comprise a different photopolymer composition. The photopolymer compositions preferably differ in the type and amount of dyes present.If different dyes, co-photoinitiators and / or wavelength-selective photoinitiators are present and / or in the first and second light-sensitive layers, these different components are preferably designed for the absorption of radiation from different wavelength ranges, in particular with different colors.

[0122] In a preferred embodiment of the invention, the first light-sensitive layer of the replication composite comprises a photopolymer composition with a first dye designed to absorb light of one color. The second light-sensitive layer of the replication composite preferably comprises a photopolymer composition with a second, different dye designed to absorb light of a different color. Preferably, the first dye is designed to absorb light from one of the wavelength ranges corresponding to red, green, and blue light.

[0123] Preferably, the second dye is designed to absorb light from another of the wavelength ranges corresponding to red, green and blue light.

[0124] For example, one of the at least two photosensitive layers may be configured for red, while another of the at least two photosensitive layers may be configured for green and / or blue. As a further example, one of the at least two photosensitive layers may be configured for blue, while another of the at least two photosensitive layers may be configured for green and / or red. Likewise, by way of example, one of the at least two photosensitive layers may be configured for green, while another of the at least two photosensitive layers may be configured for blue and / or red.

[0125] In a further preferred embodiment of the invention, a light-sensitive layer of the replication composite comprises a dye or a combination of dyes designed for the absorption of two wavelength ranges. Preferably, the two wavelength ranges differ from the wavelength range of another light-sensitive layer of the replication composite. Particularly preferably, the dye or the combination of dyes designed for two wavelength ranges is configured for the absorption of two different colors selected from red, green, or blue. The other light-sensitive layer of the replication composite is preferably configured for exposure with the third color selected from red, green, or blue. For example, a first light-sensitive layer can be designed for red and green, while a second light-sensitive layer is designed for blue.Alternatively, a first light-sensitive layer can be designed for red and blue, while a second light-sensitive layer is designed for green. As a further alternative, a first light-sensitive layer can be designed for green and blue, while a second light-sensitive layer is designed for red. This can provide a particularly compact replication array in which, for example, multiplexing occurs for two of three colors.

[0126] By varying the composition of the various photosensitive layers, the reactivity of the photosensitive layers to different regions of the electromagnetic spectrum can also be varied. The photopolymers of the photosensitive layers can, for example, comprise oligomers, monomers, and / or polymers. These oligomers, monomers, and / or polymers could, in principle, be crosslinked by radiation from a broad region of the electromagnetic spectrum. The radiation can be absorbed by reactive components of the composition, in particular by the wavelength-selective photoinitiator system, in particular the dye(s), the co-photoinitiator(s), and / or the wavelength-selective photoinitiator(s), to release free radicals or polymerization-active cationic or anionic reaction centers, which enable the polymerization of the composition.The photopolymer composition can therefore be adjusted to prevent unwanted radiation from activating the relevant components, e.g., the writing monomers. By adjusting the composition to be transmissive to unwanted regions of the spectrum, these are essentially not absorbed and do not interact with the components of the photopolymer composition. They therefore do not trigger a polymerization reaction that would produce a diffusion pattern of a volume hologram. By adding dyes that absorb selected regions of the electromagnetic spectrum, the opposite can be achieved. The absorbed radiation interacts with the photoinitiators or co-photoinitiators to release free radicals that promote polymerization. The wavelength selectivity of the photopolymer composition can thus be finely tuned.

[0127] The dye can be selected based on its transmission or absorption spectrum. Preferably, the dye has at least one absorption peak (corresponding to at least one transmission trough) at a wavelength within the desired wavelength range of the electromagnetic spectrum. It is also preferred that at least one absorption peak of the dye coincides with or overlaps with a wavelength of the radiation emitted by the exposure source with which the photosensitive layer is exposed.

[0128] The absorption peak of the dye can have an absorption maximum of at least 50%, preferably of at least 60%, more preferably of at least 70%, more preferably of at least 80%, even more preferably of at least 85%, and most preferably of at least 95%. In a preferred embodiment, a photopolymer composition for a light-sensitive layer of the replication composite comprises at least two absorption peaks. The at least two absorption peaks are preferably separated from one another by at least 50 nm, preferably at least 100 nm, particularly preferably at least 150 nm. This can be achieved by using a dye with multiple absorption peaks and / or by using multiple dyes. The resulting light-sensitive layer can advantageously be exposed to light from two wavelength ranges, preferably excluding another wavelength range.For example, two monochromatic master holograms can be replicated into a single light-sensitive layer, resulting in two holograms as a multiplex in the same layer, with the two holograms being reconstructed at different wavelengths.

[0129] In a preferred embodiment of the invention, the first light-sensitive layer of the replication composite is sensitive to exposure to radiation in a first wavelength range, wherein the first wavelength range corresponds, for example, to red light. The first wavelength range is preferably in a range between 590 and 750 nm and covers, for example, the exposure wavelengths of approximately 640 nm or approximately 660 nm. The first light-sensitive layer preferably comprises a photopolymer composition, which in turn comprises a first dye. The first dye preferably has a high absorption in the first wavelength range, wherein the high absorption is preferably at least 50%, more preferably at least 60%, even more preferably at least 70%, even more preferably at least 80%, even more preferably at least 85%, and most preferably at least 90%.High absorption in the first wavelength range preferably means that the dye exhibits such high absorption values ​​at least for selected wavelength ranges from the first wavelength range. However, it may also be preferred that the aforementioned high absorption is present on average across the entire first wavelength range. Preferably, the first dye exhibits low absorption in a second wavelength range and optionally in a third wavelength range, wherein the second and optionally third wavelength ranges are disjoint from the first wavelength range. For example, the second and third wavelength ranges can correspond to green and / or blue light.To achieve the desired sensitivity of the photosensitive layer for exposure to red light, one of the following (red-light sensitive) dyes could be used: Azure A, Brilliant Green, Brilliant Blue FCF, Cyanine 5, Cyanine 7, Fast Green FCF, Methylene Blue, New Methylene Blue, and Thionine. A red laser with a characteristic wavelength between 630 and 670 nm is preferably used for exposure of the first photosensitive layer. The red laser can be part of a laser system or a white light laser.

[0130] In a further preferred embodiment of the invention, the second photosensitive layer of the replication composite is configured for exposure to radiation of a second wavelength range, wherein the second wavelength range corresponds, for example, to green light. The second wavelength range is preferably between 490 and 590 nm. The second photosensitive layer preferably comprises a photopolymer composition, which in turn comprises a second dye. The second dye preferably has a high absorption in the second wavelength range, wherein the high absorption is preferably at least 50%, more preferably at least 60%, even more preferably at least 70%, even more preferably at least 80%, even more preferably at least 85%, and most preferably at least 90%.A high absorption in the second wavelength range preferably means that the dye has such high absorption values ​​at least for selected wavelength ranges from the second wavelength range. However, it can also be preferred that the aforementioned high absorption is present on average over the entire second wavelength range. Preferably, the second dye has a low absorption in the first wavelength range and optionally in a third wavelength range, wherein the first and optionally third wavelength ranges are disjoint from the second wavelength range. For example, the first and third wavelength ranges can correspond to red and / or blue light. In order to achieve the desired sensitivity of the light-sensitive layer for exposure to radiation of green light, a dye that absorbs green light is preferably used.As an example, one of the following (green-absorbing) dyes could be used: basic fuchsin, cyanine 3, eosin Y, eosin G, erythrosin, erythrosin B, pyronin B, pyronin Y, pyronin G, Rose Bengal, and safranin O. For exposure of the second light-sensitive layer, a green laser with a characteristic wavelength between 510 and 560 nm, for example, approximately 532 nm, is preferably used. The green laser can be part of a laser system or a white-light laser.

[0131] In a further preferred embodiment of the invention, the third photosensitive layer of the replication composite is configured for exposure to radiation of a third wavelength range, wherein the third wavelength range corresponds, for example, to blue light. The third wavelength range is preferably between 380 and 490 nm. The third photosensitive layer preferably comprises a photopolymer composition, which in turn comprises a third dye. The third dye preferably has a high absorption in the third wavelength range, wherein the high absorption is preferably at least 50%, more preferably at least 60%, even more preferably at least 70%, even more preferably at least 80%, even more preferably at least 85%, and most preferably at least 90%.A high absorption in the third wavelength range preferably means that the dye has such high absorption values ​​at least for selected wavelength ranges from the third wavelength range. However, it can also be preferred that the aforementioned high absorption is present on average over the entire third wavelength range. Preferably, the third dye has a low absorption in the first and second wavelength ranges, wherein the first and second wavelength ranges are disjoint from the third wavelength range. For example, the first and second wavelength ranges can correspond to red and / or green light. In order to achieve the desired sensitivity of the light-sensitive layer for exposure to radiation of blue light, a dye that absorbs blue light is preferably used.For example, one of the following (blue-absorbing) dyes could be used: Acridine Orange, Acridine Yellow, Acridine-3,6-diamine, Acriflavin hydrochloric acid, Brilliant Yellow, Pyrillium I (2,4,6-triphenylpyrylium tetrafluoroborate), and Riboflavin. For exposure of the third light-sensitive layer, a blue laser with a characteristic wavelength between 440 and 470 nm, e.g., approximately 450 nm, is preferably used. The blue laser can be part of a laser system or a white-light laser.

[0132] In a further preferred embodiment of the invention, the replication composite comprises a light-sensitive layer designed or sensitive for exposure to two wavelength ranges. Preferably, the two wavelength ranges correspond to two colors, preferably selected from the group consisting of red, green, and blue. A further light-sensitive layer of the replication composite is preferably designed for exposure to a different wavelength range, wherein the different wavelength range preferably corresponds to a third color, preferably red, green, or blue.

[0133] In a further preferred embodiment of the invention, the replication composite comprises a (first) light-sensitive layer sensitive to exposure to blue and green light. For example, one of the following dyes could be used: Astrazon Orange G, Darrow Red, Rhodamine 6G, Rhodamine B, and Sudan IV. A further (second) light-sensitive layer can preferably be sensitive to exposure to red light and comprise a corresponding dye.

[0134] In a further preferred embodiment of the invention, the replication composite comprises a light-sensitive layer designed for exposure to green and red light. For example, one of the following dyes could be used: Celestine Blue, DBC (2,5-bis[(4-diethylamino-2-methylphenyl)methylene]cyclopentanone), Ethyl Violet, Pinacynol Chloride, Reactive Blue 19, Victoria Blue R, and Thionin. A further (second) light-sensitive layer can preferably be sensitive to exposure to blue light and comprise a corresponding dye.

[0135] In addition to or alternatively to the use of dyes, the photoinitiators themselves can be selected to respond only to radiation in a specific wavelength range, for example, red, blue, or green. Such wavelength-selective photoinitiators can preferably be substantially inert to radiation from wavelength ranges used to expose other layers of the replication composite to avoid crosstalk. In preferred embodiments of the invention, the replication composite comprises two or more of the above-mentioned photosensitive layers (for red, green, and blue) in any order.Alternatively or additionally, the replication composite can comprise multiple photosensitive layers configured for exposure to the same wavelength, wherein the photosensitive layers comprise at least two layers configured for exposure to different regions of the electromagnetic spectrum. The use of additional layers designed for an identical or overlapping wavelength range is not excluded. Alternatively, the photosensitive layers can be configured according to any other color system, such as magenta, cyan, or yellow. One or more photosensitive layers can also be configured for exposure to any wavelength range of visible light, e.g., violet, orange, or turquoise.One or more photosensitive layers can also be configured for exposure to any wavelength in the UV, infrared, or near-infrared range of the electromagnetic spectrum. The inventive concept can thus be applied in various ways to obtain precisely aligned holograms that can be reconstructed at different wavelengths.

[0136] In a preferred embodiment of the invention, the dye is part of a dye-hydrogen donor system. In this case, tertiary amines such as n-methyldiethanolamine can be suitable hydrogen donors. Such a system is particularly advantageous as a photoinitiator for radical polymerization.

[0137] The photopolymer composition of a light-sensitive layer may further comprise a pH adjuster and / or pH stabilizer. The absorption spectra of the dyes and the reactivity of the monomers or oligomers can be influenced by adjusting the pH to a desired value.

[0138] In a further preferred embodiment of the invention, the photopolymer composition comprises one or more of the following components: a catalyst, a stabilizer, a plasticizer and a refractive index adjuster.

[0139] In a further preferred embodiment of the invention, the method comprises mixing a light-sensitive composition for each light-sensitive layer of the replication composite. Preferably, each composition comprises a different wavelength-selective dye. By mixing as part of the replication process, the properties of the replication composite, such as the number of layers, the thickness of the individual layers, the hardness of the layers, and the ranges of electromagnetic sensitivity, can be adjusted in situ. This makes the replication process particularly adaptable to small-batch production. By adjusting, in particular, the type and / or amount of dye used, the same basic composition can be used for different light-sensitive layers. This is particularly economical and efficient.

[0140] In a further preferred embodiment of the invention, the process comprises coating the photosensitive compositions one after the other in liquid form and optionally drying them to obtain the replication composite. This advantageously allows liquid photopolymers (or an alternative liquid photosensitive composition) to be used directly as starting material for replication. Preferably, the photopolymers can also be mixed in situ, and the finished mixture can be delivered to a coating module (also referred to synonymously as an "application module" within the meaning of the invention). Alternatively, the coating module is supplied with a finished, preferably light-tight, liquid photopolymer mixture. The liquid photopolymers can thus be changed between successive series or provided with different additives (in particular dyes).Thus, a wide range of liquid photopolymers can be used in the same device and adapted to the desired properties of the resulting polymer composite.

[0141] The liquid photopolymers can be present in the replication composite in a soft or liquid form prior to exposure. The ability to replicate the holograms in the still-liquid photopolymers opens up significantly greater process flexibility and can increase exposure efficiency, resulting in sharp images. With the aid of the method according to the invention, process parameters such as the layer thickness of each light-sensitive layer, its light sensitivity, or the properties of carrier films can be easily adapted to the respective desired applications. The ability to quickly change these properties without providing prefabricated light-sensitive films makes the production of small-batch holograms economical. At the same time, the polymerization of monomers or oligomers during exposure is more efficient when they are in liquid form.This is believed to be due to Brownian motion, which allows the unpolymerized monomers or oligomers to diffuse toward the polymerized diffraction gratings created by exposure. This reduces the concentration of the monomers or oligomers in the base polymer matrix of the photosensitive layer and increases their concentration in the diffraction gratings. This allows for greater refractive index contrast and sharper images.

[0142] In situ production of the replication composite is preferably carried out using one or more carrier films, a coating module, and optionally a lamination module. Preferably, a first carrier film is coated with a first liquid photopolymer composition by the coating module. Depending on the material properties of the first liquid photopolymer composition, further liquid photopolymer layers can subsequently be applied thereto. Alternatively, a second carrier film is applied to the first liquid photopolymer composition. The lamination module can serve to enclose the first liquid photopolymer between the first and second carrier films, e.g., by fusing the edges of the carrier films together. In this way, further layers of liquid photopolymer can be applied to the second carrier film.

[0143] In some embodiments, the one or more liquid photopolymer compositions are enclosed between two (outer) carrier films, with contact with the master element occurring via one of the two carrier films. It may also be preferred for the liquid photopolymer compositions to be applied directly to the surface of a master element, without separation by an intermediate carrier film.

[0144] In-situ lamination allows film thicknesses and carrier film properties to be easily adjusted between series. The liquid photopolymer can be sealed between two films by lamination to ensure high durability and prevent contamination. The lamination also protects the liquid photopolymer from unwanted deformation due to shear forces. This reduces the susceptibility to errors during hologram production.

[0145] "Laminating" or "lamination" is preferably a material-to-material, thermal joining process, preferably without auxiliary materials such as adhesives. For the purposes of the invention, this is also referred to as "lamination." The laminating module preferably comprises at least one laminating roller or lamination roller, which is heated to 5-300°C, preferably 15-200°C, or even 20-100°C.

[0146] In the context of the present invention, the term "liquid" or a liquid photopolymer is preferably defined as a substance that continuously deforms when subjected to a shear stress of any magnitude (p. 13, Munson et al., Fundamentals of Fluid Mechanics, Wiley: 2010). A liquid can also preferably be characterized by its viscosity and distinguished from other semi-solids.

[0147] The dynamic viscosity of the liquid photopolymer used as raw material at 300 K is preferably between 0.2 mPas (millipascal second) and 200 Pas (Pascal second), more preferably between 1 and 20,000 mPas. The dynamic viscosity of the liquid photopolymer at the time of exposure is preferably between 0.2 mPas and 200 Pas. It may be preferable to pre-crosslink the liquid photopolymer after application to a carrier film and before exposure, converting it into a viscoelastic state.

[0148] In a further preferred embodiment of the invention, a layer structure of the replication composite is arranged mirror-symmetrically to a layer structure of the master composite during exposure. The mirror symmetry here particularly applies to the light-sensitive layers of the replication composite. In this way, the optical function of the generated polychromatic hologram can correspond exactly to the optical function of the multilayer master hologram. When reversed, such a polychromatic hologram has the same layer structure as the master hologram. The arrangement of the layers can be configured, in particular, to minimize filter effects between the layers and to improve the efficiency of the optical function of the polychromatic hologram.

[0149] In a preferred embodiment of the invention, the polychromatic hologram is configured to fulfill the optical function of an optical component such as a lens or a mirror. This optical function can be fulfilled by a particularly compact, particularly film-shaped component that can be discreetly integrated into a product.

[0150] In a further preferred embodiment of the invention, steps a to c of the method according to the invention are repeated analogously in order to copy a polychromatic hologram composite into a second replication composite using a second master composite. In this case, the first and second master composites preferably comprise a third master hologram, while the replication composites also have a third light-sensitive layer, wherein the third master hologram and the third light-sensitive layer are designed for a third wavelength range. The three light-sensitive layers are preferably designed for red, green, and blue light. Preferably, one of the first and second replication composites is exposed using a planar wavefront. Preferably, the other of the first and second replication composites is exposed using a spherical wavefront.In this way, one of the two polychromatic holograms can be configured to convert a spherical wavefront into a planar wavefront, and the other of the two polychromatic holograms can be configured to reflect a planar waveform at a given angle.

[0151] The polychromatic holograms can perform the function of a concave mirror or a planar mirror in a very compact manner without unwanted chromatic aberration. Since the polychromatic holograms can be manufactured from light-sensitive materials with thicknesses in the micrometer range, they can perform their respective optical functions with high efficiency across multiple wavelength ranges while requiring very little space. They can therefore be discreetly integrated into AR glasses, car windshields, aircraft windows, pilot training devices, and the like.

[0152] In a further preferred embodiment of the invention, the first and second polychromatic holograms are connected to one another, wherein the first and second polychromatic holograms are preferably arranged at a distance of less than 1 mm, preferably less than 0.5 mm, particularly preferably less than 0.1 mm. The first and second polychromatic holograms preferably have a layered structure, wherein a first layer corresponds to a first wavelength range and a second layer corresponds to a second wavelength range. The polychromatic holograms are preferably arranged such that their layers are mirror-symmetrical to one another - that is, the order of the layers corresponding to each wavelength range is preferably the same from the center line outwards.

[0153] In this way, a transmissive, light-redirecting HOE with very tight tolerances and high efficiency can be created by combining two reflective polychromatic holograms, which act as concave and planar mirrors, respectively. Since only the two polychromatic holograms can be applied and bonded together in a conventional manner, e.g., by lamination, only one alignment of the two generated polychromatic holograms is required. This is a significant improvement over the current state of the art, in which six layers would have to be aligned and laminated to create such a multilayer RGB hologram. The precision of the HOE can be drastically improved.The resulting polychromatic HOE can combine the functions of the concave mirror and the planar mirror of the individual polychromatic holograms to perform complex redirection of electromagnetic beams in a very compact manner as an effective transmissive HOE.

[0154] In a further preferred embodiment of the invention, the polychromatic hologram comprises reflective and transmissive diffraction patterns, which are present in the same or in different hologram layers. This allows additional optical functions to be ensured in a compact and aberration-free manner. A polychromatic hologram can, for example, also be configured to convert a spherical wavefront into a planar wavefront. This can be combined with another polychromatic hologram that converts the planar wavefront into a freeform wavefront. Together, they advantageously form a HOE for converting a spherical wavefront into a wavefront of any shape.

[0155] In a preferred embodiment of the invention, the polychromatic hologram is produced continuously.

[0156] In a preferred embodiment of the invention, the replication composite and / or a substrate of the replication composite is in the form of a web of any length. Alternatively or additionally, the replication composite or replication composites are transported on a flow path by means of transport rollers (or “transport cylinders”), wherein the replication process takes place in particular continuously. The first and second carrier films are preferably designed as a (any length) web, so that the lamination produces a (any length) photopolymer composite web comprising a preferably liquid photopolymer layer. As a result, the replication composite can be moved through various work stations, e.g. for coating, laminating, exposing and / or fixing, at a predetermined speed and with minimal stops. The throughput can be set particularly high, even for small series. The photopolymer composite web preferably comprises at least one carrier film.

[0157] For the purposes of the invention, a "continuous" process is preferably a process in which different work steps are performed in parallel, particularly in different sections of an uninterrupted replication network and / or in different replication networks. In a continuous process, the replication network is preferably not stored temporarily.

[0158] In a further preferred embodiment of the invention, the replication composite is enclosed on both sides by a carrier film, so that all light-sensitive layers are enclosed. The light-sensitive layers between the outer carrier films can be directly layered on top of one another or separated by additional carrier layers.

[0159] In a preferred embodiment of the invention, a surface of a photosensitive layer is applied directly to the surface of a master element, without separation by an intermediate carrier film. This can be suitable for photosensitive materials that are particularly residue-free and can be peeled from the surface of the master element.

[0160] It can also be advantageous if a photosensitive layer of the replication composite remains uncovered and is oriented away from the master composite during exposure, e.g. to prevent residues from remaining on the surface of the master composite. The photosensitive layer can then be hardened in a drying and / or fixing step. This can improve the compactness of the replication composite, particularly as a carrier film can be omitted. This can be particularly advantageous if several replication composites are to be combined into more complex stacks after exposure and fixing. Alternatively, the exposed photosensitive layer can be used to emboss a pattern into the still soft photosensitive material. This can be used, for example, to create a relief hologram or to add an additional security feature to the product, to name just a few examples.

[0161] In a further preferred embodiment of the invention, the method comprises fixing the exposed replication composite, preferably by UV irradiation and / or heat treatment. This allows the light-sensitive layers to be fixed in such a way that they are no longer susceptible to the introduction of optical errors. The holograms stored in the replication composite can thus be precisely aligned with one another in a single fixing step. This process is particularly fast and error-free.

[0162] In preferred embodiments of the invention, the exposed replication composite is pre-fixed after exposure before the exposed replication composite is moved. The pre-fixing can stabilize the exposed photosensitive layers sufficiently to bring them to a further treatment station, in particular a fixing station, without affecting the already replicated hologram. This is particularly advantageous for replication composites comprising liquid or soft photosensitive layers. It can also be preferred for the replicated polychromatic hologram comprising any number of layers to be completely fixed after all exposure steps. The complete fixing can take place in situ, in particular in an exposure station, without moving the replicated polychromatic hologram. Alternatively or additionally, the complete fixing can take place in a downstream fixing station.Such fixation can be performed on a stationary, replicated polychromatic hologram or while the replicated polychromatic hologram is transported through the fixation station. The latter can allow for uniform dosing of UV irradiation and / or heat across the replicated polychromatic hologram while using lower-power devices.

[0163] In the following preferred embodiments, "fixing" preferably refers to a complete fixation, a pre-fixation, or a final step of fixing a photosensitive material that has already been pre-fixed.

[0164] For the purposes of the invention, "pre-fixing" is preferably a treatment of a light-sensitive material to reduce its sensitivity to further exposure by further electromagnetic irradiation and / or mechanical influences. Pre-fixing can also be configured to adapt the material properties of the light-sensitive material, in particular by reducing its viscosity and / or by converting the material into a semi-solid or solid form. It can be preferred that pre-fixing is used on an already exposed light-sensitive layer of a replication composite in order to stabilize the light-sensitive material and prevent further exposure of grids. The same means as for full fixation can be used for pre-fixing, in particular UV irradiation and heat treatment.It may be preferred that the process parameters used for pre-fixing, such as the intensity of UV radiation or the temperature of a heater, are adjusted to achieve the desired mechanical properties and / or the desired lower light sensitivity.

[0165] In preferred embodiments of the invention, the exposure steps and one or more fixing steps can be performed using an exposure module and a fixing module within the same workstation. This arrangement can reduce the process time for producing the polychromatic hologram. In such an embodiment, the exposure and fixing steps can be performed simultaneously or intermittently by activating the respective modules according to a process sequence. This can be achieved, for example, by applying the master composite to a circumferential surface of a rotatable roller. The composite web can be configured to be guided over and contact a portion of a rotating circumferential surface. An exposure source can direct exposure radiation onto a region of the moving composite web.Simultaneously, a device can direct UV rays or heat to a downstream region of the moving composite web. Both regions of the moving composite web can be spaced apart by up to 5 mm, up to 1 cm, or preferably up to 5 cm. This allows sufficient time for the reactions triggered by exposure to occur, while simultaneously avoiding mechanical errors by moving the exposed holograms a longer distance before fixation.

[0166] In such an embodiment, the replication composite can still be provided in web form, with further processes upstream or downstream of the workstation occurring continuously in sync with the exposure and fixation. Such further processes can include removing protective films, cutting, and / or combining a finished polychromatic hologram with other polychromatic holograms to form an HOE. Such a process can be carried out with high throughput and reliable control.

[0167] In a preferred embodiment of the invention, the master composite is mounted movably relative to the replication composite. Preferably, the master composite undergoes at least one alignment step between exposure steps to compensate for any alignment error between different master holograms of the master composite. This technique will be explained in more detail below.

[0168] The first master hologram and the second master hologram are preferably present in a layered structure in the master composite, wherein the first and second master holograms are fixed in their relative position to one another. A replication composite is preferably brought into optical contact with the master composite. The first master hologram is preferably exposed into the first light-sensitive layer of the replication composite to obtain a first hologram. For this purpose, an exposure source of the first wavelength range is preferably used, such that no radiation of the second wavelength range is emitted. The second light-sensitive layer is not affected by this. The second master hologram is then preferably aligned with respect to the replication composite by translating the master composite in a longitudinal and / or transverse direction and / or by rotating the master composite.This is preferably achieved by moving the entire master composite, the layers of which are fixed with respect to one another. The second master hologram is thus aligned with the first hologram with an improved tolerance. The second master hologram is subsequently exposed to an exposure source of the second wavelength range, in particular so as not to influence the first light-sensitive layer. The generated polychromatic hologram thus comprises at least two precisely aligned holograms, wherein the alignment tolerances of the replicated polychromatic hologram are even narrower than the alignment tolerances of the master composite. In this way, it is advantageously possible to compensate for tolerances that can arise when integrating the first and second master holograms into a master composite. Likewise, differences in the positioning of the master holograms with respect to the replication composite can be avoided.

[0169] The use of an optical fluid between the replication composite and the moving master composite can be advantageous to protect the replication composite from unwanted friction while maintaining adequate optical contact. However, it is preferred to provide the master composite as part of a master element to which the replication composite can optionally be laminated or temporarily bonded. This embodiment is discussed in more detail below.

[0170] In preferred embodiments, the master composite is part of a master element. The master element preferably comprises a master composite and a base substrate, wherein the master composite and the base substrate are mounted so as to be movable relative to one another. This solution allows one substrate of the master element to be held stationary while another substrate is rotated or translated. Preferably, the base substrate is held stationary while the master substrate (and thus the master holograms) is moved. This allows the replication composite to be brought into constant contact with a surface of the master element without frictional forces or deformation occurring between exposure steps due to relative movement at an interface. This solution enables the alignment of the master composite between exposure steps to compensate for possible tolerances during the production of the master composite.

[0171] A "base substrate" within the meaning of the invention is preferably a three-dimensional unit designed for mechanical contact with a replication composite. The base substrate is preferably rigid so that one or more layers can be laminated onto it. The base substrate is preferably mounted stationary, with a master composite preferably being mounted movably with respect to the base substrate. The base substrate preferably has analogous optical and mechanical properties to those of the master substrate. The base substrate is in particular transparent, preferably made of an optical glass or plastic. The shape and dimensions of the base substrate can be analogous to those of the master composite. Preferably, the length and / or width of the base substrate exceed the length and / or width of the master composite.

[0172] The master substrate is preferably mounted so that it can rotate and / or translate relative to the base substrate. This preferred embodiment makes it possible to compensate for any alignment errors in the master composite in the replicated polychromatic hologram. Preferably, at least two master holograms of the master composite are exposed in one exposure process, but one after the other and not simultaneously. Between the exposure steps of the at least two master holograms, the master composite is preferably aligned in its position in order to precisely position a master hologram to be exposed on an already exposed hologram in the replication composite.

[0173] In preferred embodiments of the invention, the process steps, in particular the exposure of the master composite and its optional translation and / or rotation, are controlled by a control unit. Thus, the translation and / or rotation can be carried out particularly precisely and repeatably. The process can thus follow an automated, repeating sequence. For this purpose, a control unit is preferably provided, which is configured to carry out the process steps with the aid of actuators.

[0174] The term "control unit" preferably refers to any computer unit comprising a processor, a processor chip, a microprocessor, or a microcontroller that enables automatic control of one or more actuators, e.g., a carriage, a motor, a brake, an electromagnet, an exposure source, an intensity modulator, a wavelength modulator, a galvo scanner, a movable optical component, a stage, a robot arm, etc. The components of the control unit can be conventional or individually configured for the respective implementation. Preferably, the control unit comprises a processor, a memory, and computer code (software / firmware) for controlling the components of the device.

[0175] The control unit may also comprise a programmable circuit board, a microcontroller, or other device for receiving and processing data signals from the components of the device, for example, from sensors relating to the speed of a composite web and / or the position of a master hologram, as well as other relevant sensory information. The control unit preferably further comprises a computer-usable or computer-readable medium, such as a hard disk, random access memory (RAM), read-only memory (ROM), flash memory, etc., on which computer software or code is installed. The computer code or software for controlling the components of the device may be written in any programming language or model-based development environment, e.g., but not limited to, C / C++, C#, Objective-C, Java, Basic / VisualBasic, MATLAB, Python, Simulink, StateFlow, Lab View, or Assembler.

[0176] The term "control unit is configured to" perform a specific operation, such as controlling one or more exposure sources or transporting a replication network, may include customer-specific or standard software installed on the control unit that initiates and controls these operational steps.

[0177] To perform the exposure, instructions for controlling one or more exposure sources and optionally intensity modulator(s), wavelength modulator(s), scanners, and / or movable optical components are preferably stored in a memory. The control unit preferably communicates with the memory to control the exposure. This can include switching various exposure sources on and off in a predetermined sequence. The exposure source(s) can also be intensity modulated so that different parts of the master assembly are exposed with different intensities. Additionally, a scanner and / or movable optical components can be provided to direct a collimated exposure beam in a predetermined path across the master assembly, which can cover the entire master assembly or a predetermined part of it. The optical components include, for example, mirrors, wedges, lenses, etc.

[0178] In a further preferred embodiment of the invention, the master composite comprises a master substrate, while the replication composite comprises a replication substrate. The two substrates are preferably arranged facing each other during exposure. This allows the replication composite to be securely brought into mechanical and optical contact with the master composite, protecting the light-sensitive layers and the master holograms. As described above, the replication substrate can also be flexible. In this case, the entire replication composite can be seamlessly laminated to the rigid master substrate. This stabilizes the replication composite during exposure and reduces the risk of optical losses at the interface between the replication composite and the master composite.

[0179] Preferably, an optical adhesive film or an optical fluid is applied between the master substrate and the replication substrate prior to exposure. The replication substrate and / or the master substrate is preferably provided with an anti-reflection coating. These measures can further increase the optical contact between the replication composite and the master composite and improve exposure efficiency. The optical fluid, the optical adhesive film, and the anti-reflection coating all reduce reflections at the interface between the replication composite and the master composite. Furthermore, the optical fluid can fill any gaps between the replication composite and the master composite, preventing internal reflections from occurring at these gaps. Alternatively, the optical adhesive film can improve the quality of the lamination and further stabilize the replication composite against vibrations.

[0180] For the purposes of the invention, an "optical adhesive film" is preferably a transparent film with a refractive index close to the refractive index of the master substrate, the replication substrate, and / or the light-sensitive material. The optical adhesive film is preferably designed to improve optical contact between the master composite and the replication composite, so that reflections at the interface between the master substrate and the replication substrate are reduced or eliminated. Preferably, the materials used for the optical adhesive film have identical or similar optical properties to those materials used for the master substrate, a replication substrate, or the adjacent layer of the replication composite. Preferably, the similar or identical properties include transparency, haze, stress birefringence properties, and / or the refractive index.The use of identical or similar materials enables a very close match of the refractive index of the optical adhesive film to the refractive indices of the adjacent master substrate and / or replication substrate, ensuring a transition between the adjacent refractive indices without any refractive index jumps. Reflections at the interface between the master element, the optical adhesive film, and / or the replication composite are thus largely eliminated or significantly minimized.

[0181] The optical adhesive film can preferably be removed from the surface of the master element using a peel force of less than 3 N / cm, preferably less than 1 N / cm. The optical adhesive film can preferably be removed from the replication composite using a peel force of less than 1 N / cm, more preferably less than 0.5 N / cm. This is particularly gentle on both the replication composite and the master element.

[0182] In further preferred embodiments of the invention, the optical adhesive film is part of the replication composite, so that the replication composite itself adheres to the master element. Such an optical adhesive film preferably requires a peel strength against an adjacent layer of the replication composite of at least 10 N / cm, preferably at least 50 N / cm, and even more preferably at least 100 N / cm.

[0183] In the context of the invention, the peel force of the optical adhesive film or other films or layers of the replication composite (e.g., a protective film or carrier film) can preferably be measured according to a 180-degree peel test. In preferred forms, the measurement is performed according to ASTM D903, in which six inches of the film in question are applied to a clean substrate surface. The substrate is clamped. A free end of the film is folded back 180 degrees and pulled with a force gauge. The force in Newtons required to detach each centimeter of the film from the substrate corresponds to the peel force.

[0184] An "optical fluid" within the meaning of the invention is preferably a transparent fluid with similar or identical optical properties to the master substrate, master composite, replication substrate, base substrate, and / or replication composite. The similar or identical properties preferably include transparency, haze, stress birefringence properties, and / or the refractive index. The use of an optical fluid can prevent unwanted reflections at the interfaces between components.

[0185] In a further aspect, the invention relates to a polychromatic hologram composite (or multilayer "polychromatic hologram") comprising at least a first and a second replicated hologram producible by the method according to the invention. The first and the second replicated hologram can preferably be present in one or more layers of fixed photosensitive material to provide a polychromatic hologram. The first hologram is preferably exposed to a wavelength from a first wavelength range, while the second hologram is preferably exposed to a different wavelength from a second wavelength range, so that the resulting hologram composite can diffract radiation of both wavelengths. In addition, the polychromatic hologram composite can comprise further layers such as carrier films, protective layers and / or the replication substrate.The polychromatic hologram composite is preferably a replication composite as described above, wherein at least two light-sensitive layers of the replication composite have been subjected to exposure. The light-sensitive layers of the polychromatic hologram composite can preferably be fixed so that the replicated holograms within the hologram composite are long-term stable and are not altered by the influence of further irradiation and / or exposure.

[0186] Such a polychromatic hologram composite advantageously comprises diffraction structures designed to diffract radiation with two or more different wavelengths. The diffraction structures corresponding to the different wavelengths are advantageously precisely aligned with each other, ensuring the polychromatic hologram is of high quality and fulfills its optical function very efficiently. Unwanted light filtering due to incorrect alignment of the different wavelength channels is avoided.

[0187] The polychromatic hologram composite may also comprise any other feature described above with respect to the method. Since the polychromatic hologram composite results from processing the replication composite, the polychromatic hologram composite may have an analogous layer structure and / or analogous properties to the replication composite. In particular, the polychromatic hologram composite may comprise a third layer of an exposed photosensitive material in which a third hologram is recorded. The first, second, and third holograms may be configured to be reconstructed using radiation from three different wavelength ranges, corresponding in particular to red, green, and blue. In this way, the polychromatic hologram composite may contain a clear, full-color holographic image.

[0188] Terms such as substantially, approximately, approximately, approximately, nearly, etc., preferably describe a tolerance range of less than ± 20%, preferably less than ± 10%, particularly preferably less than ± 5%, and especially less than ± 1%, and include the exact value. The average person skilled in the art recognizes that technical features, definitions, and advantages of preferred embodiments of the method according to the invention also apply to the polychromatic hologram composite according to the invention, and vice versa.

[0189] Detailed description

[0190] In the following, the invention will be explained in more detail using examples and illustrations, without being limited to these.

[0191] Short description of the figures

[0192] Fig. 1 shows the transmission spectrum of a photosensitive layer according to the prior art.

[0193] Fig. 2 shows transmission spectra for various dyes for use in a photosensitive layer according to preferred embodiments of the invention.

[0194] Fig. 3 shows further transmission spectra for various photopolymer compositions at different dye types and concentrations according to preferred embodiments of the invention.

[0195] Fig. 4 shows schematically the structure of a replication array according to a first preferred embodiment of the invention and its exposure with an RGB laser.

[0196] Fig. 5 schematically shows a method for investigating the transmission spectrum of the exposed polychromatic hologram produced according to the first embodiment (Fig. 4).

[0197] Fig. 6 shows the transmission spectrum of the exposed polychromatic hologram produced according to the first embodiment (Fig. 4).

[0198] Fig. 7 shows the transmission spectrum of another polychromatic hologram according to a second preferred embodiment of the invention, wherein the order of the light-sensitive layers is changed.

[0199] Fig. 8 shows schematically the structure of a replication array according to a third preferred embodiment of the invention and its exposure with an RGB laser.

[0200] Fig. 9 shows the transmission spectrum of the exposed polychromatic hologram produced according to the third embodiment (Fig. 8).

[0201] Fig. 10 schematically shows a method for the simultaneous exposure of a replication composite according to a fourth preferred embodiment of the invention.

[0202] Fig. 11 is a schematic representation of a polychromatic holographic-optical element (in particular a "z-hologram") comprising six holograms in a layered structure, which can be produced by the method according to the invention. Detailed Description of the Figures

[0203] Fig. 1 shows the transmission spectrum of an unexposed photosensitive layer according to the prior art in a visible region of the electromagnetic spectrum. The blue, green, and red regions of the spectrum are shaded differently. Furthermore, line 52 shows the wavelength of a red exposure laser, line 54 the wavelength of a green exposure laser, and line 56 the wavelength of a blue exposure laser. The emission spectrum shows various transmission depths, particularly in the red and green regions of the spectrum. The transmission depths (also known as "transmission minima") show the wavelengths or wavelength ranges that are absorbed by the unexposed photosensitive layer and are therefore suitable for exposure. Exposure is particularly useful in those wavelength ranges in which the transmission through the photosensitive material is less than 80%.This transmission depth can be adjusted by tuning the composition of the light-sensitive material. State-of-the-art light-sensitive materials are designed for broadband light sensitivity and therefore exhibit transmission depths of less than 80% over a broad spectral range (here: essentially across the entire visible spectrum from approximately 400 nm to 700 nm).

[0204] Figure 2 shows the transmission spectra of four different dye solutions for use in a light-sensitive material according to preferred embodiments of the invention. Suitable dyes were selected and dissolved in glycerol at concentrations between 0.5 - 5%, depending on the dye, so that each solution contains only one dye. For a blue dye (HOE Blue), acriflavine hydrochloride was used; for a green dye, either safranin O (HOE Green variant 1) or diethylsafranin (HOE Green variant 2) was used; and for a red dye (HOE Red), methylene blue was used. Each solution was applied as a liquid film between two glass plates, each measuring 50 x 50 x 1.1 mm. A UV-Vis spectrometer was calibrated with respect to the effect of the glass plates themselves.The prepared glass plates containing the various liquid films were then analyzed with a UV-Vis spectrometer in the wavelength range 400–800 nm. The results were recorded and presented graphically.

[0205] Each of the individual preferred dyes (DYE for HOE Blue, DYE for HOE Green - Variant 1, DYE for HOE Green - Variant 2, DYE for HOE Red) exhibits transmission depths (corresponding to absorption peaks) in limited regions of the electromagnetic spectrum, corresponding to the respective colors blue, red, or green. The overlap between the transmission depths of different dyes, for example, for red and blue, is small.

[0206] Shown in dashed lines are the wavelengths of radiation emitted by a red, a green, and a blue laser, respectively. A close match between the transmission minima and the emitted wavelengths of the lasers is evident. The transmittance of all selected dye solutions at these wavelengths is advantageously less than 30%. Most of the light incident on these dyes is therefore absorbed by the dyes and can be used to trigger a photopolymerization reaction for the exposure of a photosensitive material. Outside the relevant wavelengths, the dyes are significantly less absorbent (i.e., more transmissive with a transmittance greater than 85%) and therefore do not mediate a photopolymerization reaction.

[0207] For example, the "Dye for HOE Blue" solution exhibits a transmittance of approximately 20% at the characteristic wavelength of the blue exposure laser (approximately 457 nm). However, the transmittance of the same solution at the characteristic wavelengths of the green and red exposure lasers is over 90%. This means that the dye absorbs blue light but not green or red light. A photopolymer composition comprising the "Dye for HOE Blue" would therefore react to blue light but not green or red light.

[0208] The "HOE Red Dye" solution exhibits a transmittance of approximately 29% at the characteristic wavelength of the red exposure laser (approximately 640 nm). At the characteristic wavelength of the blue exposure laser, the solution exhibits a transmittance of approximately 90%. This solution also exhibits a high transmittance of approximately 85% at the characteristic wavelength of the green exposure laser. The "HOE Red Dye" therefore absorbs red light without substantially absorbing blue or green light. A photopolymer composition comprising the "HOE Red Dye" would therefore react to red light but not to green or blue light.

[0209] The same applies to the solutions "Dye for HOE Green - Variant 1" and "Dye for HOE Green - Variant 2," which exhibit very low transmission (5-12%) at the characteristic wavelength of the green exposure laser (approx. 532 nm) and much higher transmission at the characteristic wavelengths of the blue and red exposure lasers. This transmission can be fine-tuned by adjusting the dye concentration in the solution.

[0210] By applying different dyes in optimized concentrations to different light-sensitive layers of a replication composite according to the invention, the respective different light-sensitive layers can in particular achieve a wavelength selectivity in which a first light-sensitive layer is sensitive to radiation in a first wavelength range but not to radiation in a second wavelength range, and wherein a second light-sensitive layer is sensitive to radiation in the second wavelength range but not to radiation in the first wavelength range.

[0211] Figure 3 shows the transmission spectra of four different photopolymer compositions prepared with the four different dyes shown in Figure 2. The various photopolymer compositions are sensitive to radiation from a red, green, or blue laser, with the characteristic wavelengths of the lasers shown as dashed lines. Each tested photopolymer composition comprises a base composition. The base composition includes a writing monomer (or "photoactive monomer"), a matrix monomer (for the polymer matrix), and a photoinitiator system. A dye was added to each of these base compositions as a concentrate, so that the photopolymer composition exhibits a desired wavelength selectivity.While the photoinitiator system of the base composition preferably has no or only reduced wavelength selectivity and comprises, for example, a co-photoinitiator and / or photoinitiator, the wavelength selectivity of the photoinitiator system can be adjusted by adding a dye. The concentration of the dyes in the photopolymer composition has been optimized for wavelength selectivity.

[0212] A first photopolymer composition comprises a blue dye (“Dye for HOE Blue”, here: Acriflavine hydrochloride) in a concentration of 0.045 wt-%, a second photopolymer composition comprises a first green dye (“Dye for HOE Green - Variant 1”, here: Safranin O) in a concentration of 0.01 wt-%, a third photopolymer composition comprises a second green dye (“Dye for HOE Green

[0213] - Variant 2", here: diethylsafranine) in a concentration of 0.09 m-% and a fourth photopolymer composition comprises a red dye ("dye for HOE Red", here: methylene blue) in a concentration of 0.015 m-%.

[0214] To record the transmission spectra, the photopolymer compositions were introduced as a liquid film between two glass plates (50 x 50 x 1.1 mm) in the same way as the solutions shown in Fig. 2 and measured with a calibrated UV-Vis spectrometer in the wavelength range 400

[0215] - 800 nm exposed.

[0216] The transmission was recorded and is shown in Fig. 3. The spectra show that each photopolymer composition exhibits low transmission (specifically <80%), i.e., high absorption, at the characteristic wavelength of the relevant exposure laser. At the characteristic wavelengths of the other exposure lasers, the photopolymer compositions do not exhibit high absorption, i.e., in particular, the transmission is above 85%. Each photopolymer composition is therefore designed for exposure to radiation from a specific wavelength range and is essentially insensitive to other wavelength ranges.

[0217] For example, the composition "Photopolymer for HOE Green - Variant 2" exhibits a low transmittance of approximately 60% at the characteristic wavelength of the green exposure laser (shown as a dashed line at approximately 530 nm). At the same time, the composition has a high transmittance of approximately 80% at the characteristic wavelength of the blue exposure laser and a high transmittance of approximately 90% at the characteristic wavelength of the red exposure laser. Exposure of a replication composite comprising a photosensitive layer made of the "Photopolymer for HOE Green - Variant 2" with an RGB laser would therefore only produce a green diffraction pattern in the photosensitive layer. The red and blue rays would have essentially no effect on this material. In particular, no undesirable red or blue diffraction structures would be formed in the photosensitive layer.

[0218] Two or more of the photopolymer compositions (in particular selected from photopolymer for HOE Red, photopolymer for HOE Green - variant 1, photopolymer for HOE Green - variant 2, or photopolymer for HOE Blue) can be exposed in one exposure process, in particular simultaneously, without generating undesirable patterns in an incorrect photopolymer composition. Such photopolymer compositions are therefore particularly suitable for use in the light-sensitive layers of a replication composite according to the invention.

[0219] Fig. 4 schematically shows the structure of a replication composite 44 according to a first preferred embodiment of the invention. The replication composite 44 comprises a first carrier film 48, onto which a first light-sensitive layer 14 is applied. In this embodiment, the first light-sensitive layer 14 is sensitive to radiation in the green and blue regions of the electromagnetic spectrum. For this purpose, the first light-sensitive layer 14 comprises the dye for HOE Blue from Fig. 2, which absorbs blue light particularly well, and the dye for HOE Green - variant 1 from Fig. 2, which absorbs green light particularly well. The replication composite 44 further comprises a second carrier film 48, which is coated with a second light-sensitive layer 16. The second light-sensitive layer 16 is particularly sensitive to radiation from the red region of the electromagnetic spectrum.For this purpose, the second light-sensitive layer 16 comprises the dye for HOE Red shown in Fig. 2, which absorbs red light particularly well. The coated first and second carrier films are applied to one another such that a carrier film 48 is present between the first 14 and the second 16 light-sensitive layers. The second light-sensitive layer 16 is uncovered on one side. Together, these layers form the replication composite 44.

[0220] The replication composite 44 is projected onto a mirror 50, which serves as a reflective master hologram for the purposes of the embodiments explained here. The mirror 50 is a stainless steel optical element with a thickness of 0.8 mm. The unexposed replication composite is irradiated with an RGB laser to simultaneously expose the first and second photosensitive layers 14, 16. For this purpose, a reference beam 26 from the RGB laser is directed onto the mirror 50 at an orthogonal angle of incidence of 90°. The reference beam traverses the photosensitive layers 14 and 16 before being reflected back by the mirror 50 to generate an object beam. The reference beam 26 interferes with the object beam in the photosensitive layers 14 and 16. This triggers a photopolymerization reaction that forms diffraction patterns in the photosensitive materials.Due to the wavelength selectivity of the layer, the red portion of the RGB radiation acts on the second light-sensitive layer to generate a red hologram. In this first embodiment, the red radiation has a wavelength of 660 nm and is applied at a dose of 151 mJ / cm. 2 The green and blue components of the RGB radiation act on the first light-sensitive layer to create a green-blue hologram. In this example, the green radiation has a wavelength of 532 nm and is applied at a dose of 57 mJ / cm 2 The blue radiation has a wavelength of 457 nm and is applied at a dose of 75 mJ / cm 2 The holograms are then fixed using UV radiation and / or heat. The fixed replication composite 44 is subsequently removed from the mirror 50.

[0221] Figure 5 shows an examination of the transmission spectrum of the exposed replication composite 44 of the first embodiment. The replication composite 44 is applied to a transparent glass plate 52 and reconstructed with a white wavefront 32. In this case, the white light is generated by an RGB laser, so it has known red, green, and blue components. Since the holograms produced are reflection holograms, the light of the inscribed wavelengths is reflected. Light from other regions of the visible spectrum is transmitted through the replication composite 44. A transmission spectrum is recorded for the replication composite 44 and for the individual holograms in the separate light-sensitive layers 14 and 16.

[0222] The results of the study are shown in Figure 6. The black line shows transmission minima at approximately 450 nm, 525 nm, and 650 nm. These minima essentially correspond to the RGB wavelengths used for exposure. Slight deviations from the laser wavelengths may be due to shrinkage / swelling of the light-sensitive layers. The transmission spectrum shows that the replication composite exhibits 44 reflective diffraction patterns that reflect red, green, and blue light.

[0223] After separating the coated carrier films 48 from each other, the individual light-sensitive layers could also be examined. The upper line (red) shows the transmission spectrum of the second light-sensitive layer 16. The transmission spectrum includes a single transmission minimum in the red region of the visible spectrum. In the green and blue regions, the second light-sensitive layer 16 is essentially completely transmissive. This shows that a red hologram was inscribed in the exposed second light-sensitive layer 16, but no blue or green hologram. The light-sensitive layer 16 therefore effectively selected the red radiation of the RGB laser, while no interference pattern was generated by the simultaneous exposure to the green or blue light components.

[0224] The middle line (green) shows the transmission spectrum of the first light-sensitive layer 14. The transmission spectrum comprises only two transmission minima in the green-blue region of the visible spectrum. In the red region of the spectrum, the first light-sensitive layer 14 is essentially completely transmissive. This shows that two holograms (green and blue) were inscribed as a multiplex in the exposed first light-sensitive layer 14, but no red hologram. The light-sensitive layer 14 therefore effectively selected the green and blue radiation of the RGB laser, while no interference pattern was generated by the simultaneous exposure to red light components.

[0225] Figure 7 shows the transmission spectrum for the construction of a further replication assembly 44 according to a second embodiment of the invention. In this embodiment, the same compositions of the photosensitive layers as in the first embodiment (see Figures 4-6) are used. However, the order of the layers is changed so that the second photosensitive layer 16, which is sensitive to radiation in the green and blue ranges of the electromagnetic spectrum, is arranged above the first photosensitive layer 14, which is sensitive to radiation in the red range of the electromagnetic spectrum. The same parameters were used for exposure with an RGB laser and a mirror. The effect of the layer arrangement was then investigated by reconstruction with a white wavefront 32.The recorded transmission spectra for the entire replication assembly 44, as well as for the separate light-sensitive layers 14 and 16, are shown in Fig. 7. The recorded transmission spectrum was largely similar to that of Fig. 6, except that the green and blue transmission minima were deeper and the red transmission minimum was somewhat flatter. This suggests that—with a slight adjustment of the replication parameters—the wavelength selectivity of each light-sensitive layer is largely insensitive to the layer's position within a stack.

[0226] Fig. 8 shows a further layer structure of a replication composite 44 according to a third preferred embodiment, comprising a first carrier film 48, a first light-sensitive layer 14, a second light-sensitive layer 16 and a second carrier film 48.

[0227] In this embodiment, the same compositions of the light-sensitive layers of the structure of the first and second embodiments (see Figs. 4-7) are used. The light-sensitive layer 14 is therefore sensitive to radiation in the red region of the electromagnetic spectrum and, for this purpose, comprises the dye for HOE Red (see Fig. 2). The light-sensitive layer 16 is therefore sensitive to radiation in the green and blue regions of the electromagnetic spectrum and, for this purpose, comprises the dyes for HOE Blue and for HOE Green - Variant 1 (see Fig. 2).

[0228] The replication composite 44 was applied to the mirror 50 using an optical adhesive film 30 and exposed as described for Fig. 4. The exposure parameters were adjusted so that the red radiation in a dose of 31 mJ / cm 2 , the green radiation at a dose of 19 mJ / cm 2 and the blue radiation at a dose of 38 mJ / cm2 was used. The exposed and fixed replication composite 44 was then removed from the mirror 50 and applied to the glass plate 52. The transmission spectrum of the replication composite 44 was then examined. Due to the difficulty of separating the individual light-sensitive layers 14, 16 from one another, since in this case they are not separated by a carrier film, only the entire replication composite was analyzed. Fig. 9 shows the transmission spectrum of the replication composite 44 according to Fig. 8. In each of the blue, green, and red regions of the spectrum, three large depths can be seen. This shows that even without a separating carrier film, the light-sensitive layers in direct contact are suitable for generating different, separated partial holograms (RGB).

[0229] Fig. 10 schematically shows an exposure process according to a fourth preferred embodiment of the invention. The master composite 2 comprises a master substrate 10, which can be a glass plate, for example. A first master hologram 8 is laminated to a surface of the master substrate 10. The first hologram 8 is designed for a first wavelength range A1, for example, a blue region of the visible spectrum. A second master hologram 6 is laminated to the first master hologram 8. The second master hologram 6 is designed for a second wavelength range A2, in particular a green region of the visible spectrum. A third master hologram 4 is in turn laminated to the second master hologram 6 and forms part of the layer structure of the resulting master composite 2. The third master hologram 4 corresponds to a third wavelength range A3, for example, a red region of the visible spectrum.In the exemplary embodiment, the three master holograms 4, 6 and 8 are reflection holograms and have an optical function for bundling incident radiation.

[0230] A replication composite 44 comprises a first light-sensitive layer 14, which is designed for a first wavelength range A1, for example, a blue region of the visible spectrum. The replication composite 44 further comprises a second light-sensitive layer 16, which is designed for a first wavelength range A2, for example, a green region of the visible spectrum. The replication composite 44 additionally comprises a third light-sensitive layer 18, which is designed for a third wavelength range A3, for example, a red region of the visible spectrum. The replication composite 44 has a replication substrate 48, which is in the form of a transparent film or a rigid plate.

[0231] The replication composite 44 is illuminated with an RGB laser. RGB rays are simultaneously directed onto the master composite 2. These rays include the reference rays 26, which traverse the light-sensitive layers and are reflected by the respective master hologram 4, 6, or 8 of the master composite 2. The reflected rays include the object rays 28, which traverse the light-sensitive layers and converge to a point according to the optical function of the master composite 2. The reference rays 26 interfere with the object rays 28 in the light-sensitive layers. However, each light-sensitive layer only reacts to radiation from the wavelength range that the layer absorbs. This creates a red hologram 140, a green hologram 160, and a blue hologram 180. Together, these holograms form a first polychromatic hologram 20. Fig.Figure 11 shows a HOE comprising a first polychromatic hologram 20 and a second polychromatic hologram 22, each produced according to the method according to the invention. Each of the two polychromatic holograms is an RGB hologram, with the RGB holograms arranged in a mirrored order to one another. The resulting HOE (which can also be referred to as a "z-hologram" due to the beam guidance) thus has, for example, a BGRRGB layer structure. While the first polychromatic hologram 20 was produced as shown in Figure 10, the second polychromatic hologram 22 has a planar reflective optical function and is exposed with a planar wavefront.

[0232] The first polychromatic hologram 20 converts a spherical reconstruction wavefront 32 into a planar wavefront. A red component of the reconstruction wave from 32 is reflected by the third hologram 180 to form the red reflected rays 38. A green component of the reconstruction wave from 32 is reflected by the second hologram 160 to form the green reflected rays 36. Similarly, a blue component of the reconstruction wave from 32 is reflected by the first hologram 140 to form the blue reflected rays 34.

[0233] The second polychromatic hologram 22 then reflects the light beams 38, 36, and 34 to create the planar deflected wavefront 46. The holograms 140, 160, and 180 of the second polychromatic hologram reflect the blue light beams 34, the green light beams 36, and the red light beams 38, respectively. Thus, the planar wavefront 46 can preferably appear white. It can also have a color determined by the intensities of the reflected beams. A complex light-deflecting function can thus be performed in a precise and compact manner.

[0234] List of reference symbols

[0235] 2 Master's network

[0236] 4 first master hologram

[0237] 6 second master hologram

[0238] 8 third master hologram

[0239] 10 Master substrate

[0240] 14 first light-sensitive layer

[0241] 16 second light-sensitive layer

[0242] 18 third light-sensitive layer

[0243] 20 first polychromatic hologram

[0244] 22 second polychromatic hologram

[0245] 24 HOE

[0246] 26 Reference beam

[0247] 28 Object beam

[0248] 30 optical adhesive films

[0249] 32 Reconstruction wavefront

[0250] 34 reflected waves of the first wavelength range

[0251] 36 reflected wave of the second wavelength range

[0252] 38 reflected wave of the third wavelength range

[0253] 44 Replication network

[0254] 46 deflected wavefront

[0255] 48 carrier film

[0256] 50 mirrors

[0257] 52 glass

[0258] 54 Wavelength of the first exposure source

[0259] 56 Wavelength of the second exposure source

[0260] 58 Wavelength of the third exposure source

[0261] 140 first replicated hologram 160 second replicated hologram

[0262] 180 third replicated hologram

Claims

PATENT CLAIMS 1. A method for replicating a polychromatic hologram composite comprising the following steps: a) providing a master composite comprising a first master hologram and a second master hologram, wherein the first master hologram is wavelength-selective for radiation having a first wavelength range and the second master hologram is wavelength-selective for radiation having a second wavelength range, b) providing a replication composite comprising a first and second light-sensitive layer, wherein the first light-sensitive layer is sensitive to radiation in the first wavelength range but not to radiation in the second wavelength range, and wherein the second light-sensitive layer is sensitive to radiation in the second wavelength range but not to radiation in the first wavelength range, c) exposing the master composite comprising the first and second master holograms,to replicate a first and a second hologram into the first and second photosensitive layers., 2. Method according to claim 1, characterized in that the exposure of the master composite comprising the first and the second master hologram takes place in one exposure process, preferably simultaneously.

3. Method according to one of the preceding claims, characterized in that the master composite comprises a third master hologram which is wavelength-selective for radiation having a third wavelength range and the replication composite comprises a third light-sensitive layer, wherein the third light-sensitive layer is sensitive to radiation in the third wavelength range but not to radiation in the first or second wavelength range.

4. Method according to the preceding claim, characterized in that one of the first, second or third wavelength ranges corresponds to red light, one of the first, second or third wavelength ranges corresponds to green light and one of the first, second or third wavelength ranges corresponds to blue light.

5. Method according to one of the preceding claims, characterized in that the first and second light-sensitive layers of the replication composite comprise a different photopolymer composition, wherein the photopolymer compositions differ in the type and amount of dyes present.

6. Method according to one of the preceding claims, characterized in that during the exposure, a layer structure of the replication composite is arranged mirror-symmetrically to a layer structure of the master composite.

7. Method according to one of the preceding claims, characterized in that the master composite comprises a master substrate and the replication composite comprises a replication substrate, wherein preferably an optical adhesive film or an optical liquid is applied between the master substrate and the replication substrate before exposure, wherein preferably the replication substrate and / or the master substrate is provided with an anti-reflection coating.

8. Method according to one of the preceding claims, characterized in that the exposure is carried out by at least a first and a second exposure source, wherein the first exposure source emits radiation with a wavelength in the first wavelength range and the second exposure source emits radiation with a wavelength in the second wavelength range and / or wherein the exposure is carried out by at least one polychromatic exposure source, wherein the polychromatic exposure source emits radiation with a wavelength in the first wavelength range and the second wavelength range.

9. Method according to one of the preceding claims, characterized in that at least one laser and / or one light-emitting diode (LED), for example a scanning RGB laser, is used for the exposure.

10. Method according to one of the preceding claims, characterized in that the method further comprises fixing the exposed replication composite, preferably by irradiation with UV radiation and / or heat treatment.

11. A method according to any one of the preceding claims, characterized in that the method comprises mixing a photosensitive composition for each photosensitive layer, each composition comprising a different wavelength-selective dye.

12. A method according to any one of the preceding claims, characterized in that the method comprises coating the photosensitive compositions successively in liquid form and drying to obtain a replication composite.

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

14. Method according to one of the preceding claims, characterized in that steps a to c are repeated analogously in order to copy a polychromatic hologram composite into a second replication composite using a second master composite, wherein preferably the exposure of one of the two replication composites is carried out by means of a planar wavefront and the exposure of the other of the two replication composites is carried out by means of a spherical wavefront.

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

16. A polychromatic hologram composite comprising at least a first and a second replicated hologram producible by a method according to any one of the preceding claims.

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