Device and method for recording holograms

Abstract

Method and device for recording holograms, wherein the device comprises a first device and a second device, wherein the first device is designed to generate wavefront-printed holograms and the second device is designed to generate analog holograms, and wherein the device is designed to expose a dedicated area (302) or a plurality of dedicated areas (302) of the photopolymer film (300) with the first device in a first step by means of a sequential recording process in the same holographic photopolymer film (300), and in a second step to expose the photopolymer film (300) exposed in the first step, including at least a portion of the dedicated areas (302), with the second device.

Description

Prior ArtThe invention relates to an apparatus and a method for recording holograms.Fields of application for holograms, for example holographic optical elements (HOEs), are novel display or sensor systems. Possible fields of application such as smart glasses or transparent display systems based on holographic scattering discs have a great potential and can be realized by using HOEs.Hologram recording methods are based on the fact that wavefronts (laser beams) with a suitable aperture cone and angle and shaped coherently with respect to one another are caused to interfere and this interference pattern is exposed to light in a suitable photosensitive material (usually photopolymer film).Holography recording devices for recording so-called analog holograms are based on conventional optical elements which are implemented for beam shaping / beam deflection. Analog holograms are typically recorded in a single exposure step by appropriately widened wavefronts.In comparison with classic analog holograms, the holographic wavefront printing offers in particular a possibility of producing HOEs with particularly complex holographic structures. In this case, individual sub-holograms (Hogel) are exposed in a matrix structure in succession in a sequential exposure process. The size of a hollow, usually in square form, varies between 50 μm and about 1 mm edge length. The holographic function of each sub-hologram can be individually adapted in this case. This entails a great freedom for the design of the optical function of the HOE. The adaptation of the holographic function of a hollow is realized by adaptive optics, usually by so-called spatial light modulators (SLMs). Further possibilities are provided by transmissive, adaptive phase plates or deformable mirrors.Disclosure of the InventionFor the mass production of HOEs, replication of a hologram produced by the holographic wavefront exposer can be provided. The replication of the hologram can then be carried out cost-effectively and time-effectively in a roll-to-roll process.The hologram is produced with two recording waves with a holographic wavefront exposer. The wavefronts of the two recording waves are adjusted individually and independently of one another. The angular and wavelength bandwidth is increased in a targeted manner, in particular, in order to achieve a specific target value for the diffraction efficiency of the hologram.A stack of multiple holograms may be provided. For example, in the field of data glasses development, stacks of multiple holograms are used to realize optical functions by the HOE. For example, a stack of three holograms is used. The stack comprises, for example, three photopolymer films each having a hologram in order to represent functions in the full color space RGB with one photopolymer film each per color or eye tracking in the infrared range (IR) with two photopolymer films for two of the colors from the color space RGB and one of the photopolymer films for IR.By means of the apparatus and the method according to the independent claims, the properties of classical analog holograms are combined with the diversity of wavefront-printed holograms in a single photopolymer layer.The device enables a plurality of holographic functions to be realized in a single layer of hologram film.The device prevents unwanted double images and other disturbing effects. This enables the same functionality to be realized as in a stack with layers of holograms in a single hologram or with fewer layers of holograms in the stack.The device makes it possible to produce complex HOEs which realize a multiplicity of optical functions by means of an intermittent arrangement.This allows a plurality of functions, for example RGB, to be combined by spatial multiplexing. For example, the holographic functions can be divided into different groups of microgels and distributed over the entire area of the HOE in different arrangements.The apparatus for recording holograms comprises a first device and a second device, wherein the first device is configured to generate wavefront-printed holograms and the second device is configured to generate analog holograms, wherein the apparatus is configured to expose one or more dedicated regions of the photopolymer film to the first device in a first step by a sequential recording process in the same holographic photopolymer film, and to expose the photopolymer film exposed in the first step including at least part of the dedicated regions to the second device in a second step. By combining analog and digital recording technology, a combination of holographic functions in the visible as well as in the IR spectral range is possible. Moreover, holograms having a variety of different angular configurations may be realized.The device is preferably designed to leave one or more dedicated regions of the photopolymer film unexposed in the first step. This means that the device is designed to form the analog holograms in the second step, in particular in the regions which were not previously exposed in the first step. Holograms, i.e. volume diffraction gratings, have already formed in the already exposed regions, so that no holograms or holograms of significantly weaker configuration are recorded in these regions. The function of the recorded analog holograms is completely independent of the previously recorded wavefront-printed holograms and can realize other holographic functions.It can be provided that the first means for generating wavefronts of light of a wavelength visible to humans is configured, wherein the apparatus is configured to expose one or more dedicated regions of the photopolymer film to the wavefronts of light of the wavelength visible to humans in the first step, and that the second means for generating holograms is configured to infrared light, wherein the apparatus is configured to expose one or more dedicated regions of the photopolymer film to the infrared light in the second step. Holographic functions in the IR range can thereby be realized.Whether an exposure is possible in the pre-exposed areas depends here on the previously introduced recording energy or the dyes consumed in the photopolymer. An advantageous use or no or partial hologram formation can be achieved in the pre-exposed areas depending on the application.The device is preferably designed to expose at least one dedicated region of the photopolymer film in the first step to a recording energy which is matched to a dye in the photopolymer film in such a way that no imageable dye is left in the at least one dedicated region of the photopolymer film for exposure in the second step.The device is preferably designed to expose at least one dedicated region of the photopolymer film in the first step to a recording energy which is matched to a dye in the photopolymer film in such a way that dye still capable of being exposed is left in the at least one dedicated region of the photopolymer film for the exposure in the second step.The apparatus preferably comprises an incoherent white light source and is configured to expose the photopolymer film in the sequential recording process in a third step after exposure of the photopolymer film to incoherent light from the white light source by the first device and the second device. Exposure with the first device and the second device produces an interference pattern in the photopolymer film. Following exposure of the interference pattern, the photopolymer of the photopolymer film is bleached by the incoherent white light source. The bleaching causes the original photosensitive material of the photopolymer film to be brought into a stationary state. The bleaching process causes crosslinking of the polymer and fixing of the holographic structure. The bleaching process is also decisive for the transparency properties of the resulting hologram, i.e. the amount of scattered light.A method for recording holograms provides that the method comprises a sequential recording process in the same holographic photopolymer film, wherein in a first step one or more dedicated regions of the photopolymer film are exposed to a first device, wherein the first device is configured to generate wavefront-printed holograms, and in a second step the photopolymer film exposed in the first step, including at least a part of the dedicated regions, is exposed to a second device, wherein the second device is configured to generate analog holograms.It is preferably provided that in the first step, a dedicated region is left unexposed or a plurality of dedicated regions of the photopolymer film are left unexposed.It can be provided that in the first step, one or more dedicated regions of the photopolymer film are exposed to wavefronts of light of a human visible wavelength, wherein the first device is configured to generate wavefronts of light of a human visible wavelength, and the wavefronts are generated with the first device, and in the second step, one or more dedicated regions of the photopolymer film are exposed to infrared light, wherein the second device is configured to generate holograms is exposed to infrared light, and the infrared light is generated with the second device.For example, in the first step, at least one dedicated region of the photopolymer film is exposed to a recording energy which is matched to a dye in the photopolymer film in such a way that no imageable dye is left in the at least one dedicated region of the photopolymer film for exposure in the second step.For example, in the first step, at least one dedicated region of the photopolymer film is exposed to a recording energy which is matched to a dye in the photopolymer film in such a way that dye still capable of being exposed is left in the at least one dedicated region of the photopolymer film for the exposure in the second step.For fixing, the photopolymer film is exposed, for example in the sequential recording process, in a third step after exposure of the photopolymer film to incoherent light from a white light source by means of the first device and the second device.The method can provide that at least one hologram is produced by the exposure with the first device and a master hologram is produced by the exposure of the at least one hologram with the second device, wherein at least one other hologram is produced in a roll-to-roll process on the basis of the master hologram.Further embodiments can be seen from the following description and the drawing. The drawing shows: FIG. 1 shows a schematic representation of an apparatus for recording holograms, FIG. 2 shows a flow chart with steps of a method for recording holograms, FIG. 3 shows a photopolymer film.FIG. 1 schematically illustrates a device 100 for recording holograms.The apparatus 100 comprises a first device 102, a second device 104 and a white light source 106. The first device 102 is configured to generate wavefront-printed holograms. The second device 104 is designed to generate analog holograms. The white light source is designed to generate incoherent light for fixing the hologram.Depending on the intended application, the first device 102 can be designed to generate wavefront-printed holograms only with light of a wavelength visible to humans, or to generate wavefront-printed holograms with light of a wavelength visible to humans and infrared light.Depending on the intended application, the second device 104 can be designed to generate analog holograms only with light of a wavelength visible to humans, or to generate analog holograms with light of a wavelength visible to humans and infrared light.For example, the first device 102 is configured to generate wavefront-printed holograms with light from the RGB color space. For example, the second device 104 is designed to generate analog holograms with light from the RGB color space.For example, the first device 102 is configured to generate wavefront-printed holograms with light of the three different colors from the RGB color space. For example, the second device 142 is designed to generate analog holograms with light of the three different colors from the RGB color space.For example, the first device 102 is configured to generate wavefront-printed holograms with light of two of the three different colors from the RGB color space and with infrared light. For example, the second device 142 is designed to generate analog holograms with light of two of the three different colors from the RGB color space and with infrared light.The apparatus 100 is designed to carry out a method for recording holograms.FIG. 2 shows a flow chart of the method. The method comprises a sequential recording process in the same holographic photopolymer film.The method comprises a first step 202.In the first step 202, a dedicated area or areas of the photopolymer film are exposed to the first device 102.That is, depending on the application, a dedicated area or areas of the photopolymer film having wavefronts are exposed only to light of one or more colors of the human-visible wavelength, or to light of one or more colors of the human-visible wavelength and infrared light.In the first step 202, at least one dedicated area is left unexposed in the example. It may be provided to leave one or more dedicated areas of the photopolymer film unexposed.Depending on the application, it can be provided in the first step 202 that at least one dedicated region of the photopolymer film is exposed to a recording energy which is matched to a dye in the photopolymer film in such a way that no imageable dye is left for further exposure in the at least one dedicated region of the photopolymer film.Depending on the application, it can be provided in the first step 202 that at least one dedicated region of the photopolymer film is exposed to a recording energy which is matched to a dye in the photopolymer film in such a way that dye still capable of being exposed is left for a further exposure in the at least one dedicated region of the photopolymer film.The energy introduced by exposure is the product of power and duration. It can be provided to preset the recording energy for the desired result by adjusting the power or the duration of the exposure.The input energy is controlled, for example, such that the input energy is less than the energy that consumes the entire modulation budget.A second step 204 is then carried out.In the second step 204, the photopolymer film 300 exposed in the first step 202, including at least a part of the dedicated regions, is exposed with the second device 104.Depending on the application, this means that regions of the photopolymer film including at least one dedicated region already pre-exposed in the first step or a plurality of dedicated regions of the photopolymer film already pre-exposed in the first step are exposed to wavefronts only from light of one or more colors of the wavelength visible to humans, or to light of one or more colors of the wavelength visible to humans and infrared light.Optionally, a third step 206 is then carried out.In the third step 206, the photopolymer film is exposed to incoherent light from the white light source 106. For example, the photopolymer film is exposed until the hologram is fixed.It can be provided that, in order to produce a plurality of holograms, the first step 202 in the method is carried out for each hologram and the second step 204 is carried out only for one master hologram. Instead of exposing the other holograms already exposed in the first step 202, the method can provide a roll-to-roll process for producing the holograms as a function of the master hologram.Referring now to Figure 3, a holographic photopolymer film 300 is shown schematically.Photopolymer film 300 includes a plurality of regions 302.In FIG. 3, the dedicated areas 302 exposed by the first device 102 are shaded.

Claims

Apparatus (100) for recording holograms, characterized in that the apparatus (100) has a first device (102) and a second device (104), wherein the first device (102) is designed for generating wavefront-printed holograms and the second device (104) is designed for generating analog holograms, and in that the apparatus (100) is designed, by a sequential recording process in the same holographic photopolymer film (300), to expose one dedicated region (302) or a plurality of dedicated regions (302) of the photopolymer film (300) to the first device (102) in a first step, and to expose the photopolymer film (300) exposed in the first step, including at least part of the dedicated regions (302), to the second device (104) in a second step.The device (100) according to claim 1, characterized in that the device (100) is configured to leave one or more dedicated areas (302) of the photopolymer film (300) unexposed in the first step.The device (100) according to any one of the preceding claims, characterized in that the first means (102) for generating wavefronts of light of a wavelength visible to humans is configured, in the first step, to expose one or more dedicated regions (302) of the photopolymer film (300) to the wavefronts of light of the wavelength visible to humans, and in that the second means (104) for generating holograms is configured to expose one or more dedicated regions (302) of the photopolymer film (300) to the infrared light, in the second step.Device (100) according to one of the preceding claims, characterized in that the device (100) is designed, in the first step, to expose at least one dedicated region (302) of the photopolymer film (300) with a recording energy which is matched to a dye in the photopolymer film (300) in such a way that no imageable dye is left in the at least one dedicated region (302) of the photopolymer film (300) for the exposure in the second step.Device (100) according to one of the preceding claims, characterized in that the device (100) is designed, in the first step, to expose at least one dedicated region (302) of the photopolymer film (300) with a recording energy which is matched to a dye in the photopolymer film (300) in such a way that dye still capable of being exposed is left in the at least one dedicated region (302) of the photopolymer film (300) for the exposure in the second step.The device (100) according to any one of the preceding claims, characterized in that the device (100) comprises an incoherent white light source (106) and is configured to expose the photopolymer film (300) in the sequential recording process in a third step after exposing the photopolymer film (300) with the first device and the second device to incoherent light from the white light source (106).Method for recording holograms, characterized in that the method comprises a sequential recording process in the same holographic photopolymer film (300), wherein in a first step (202) a dedicated region (302) or a plurality of dedicated regions (302) of the photopolymer film is exposed to a first device (102), wherein the first device (102) is configured to generate wavefront-printed holograms, and in a second step (204) the photopolymer film (300) exposed in the first step (202), including at least a part of the dedicated regions (302), is exposed to a second device (104), wherein the second device (104) is configured to generate analog holograms.Method according to claim 7, characterized in that in the first step (202), one dedicated area (302) is left unexposed or several dedicated areas (302) of the photopolymer film (300) are left unexposed.Method according to one of claims 7 or 8, characterised in that in the first step (202), one or more dedicated regions (302) of the photopolymer film (300) are exposed to wavefronts of light of a wavelength visible to humans, wherein the first device (102) is configured to generate wavefronts of light of a wavelength visible to humans, and the wavefronts are generated with the first device (102), and in the second step (204), one or more dedicated regions (302) of the photopolymer film (300) are exposed to infrared light, wherein the second device (104) is configured to generate holograms with infrared light, and the infrared light is generated with the second device (104).Method according to one of Claims 7 to 9, characterized in that, in the first step (202), at least one dedicated region (302) of the photopolymer film (300) is exposed to a recording energy which is matched to a dye in the photopolymer film (300) in such a way that no imageable dye is left in the at least one dedicated region (302) of the photopolymer film (300) for the exposure in the second step (204).Method according to one of Claims 7 to 9, characterized in that, in the first step (202), at least one dedicated region (302) of the photopolymer film (300) is exposed to a recording energy which is matched to a dye in the photopolymer film (300) in such a way that dye still capable of being exposed is left in the at least one dedicated region (302) of the photopolymer film (300) for the exposure in the second step (204).Method according to one of Claims 7 to 11, characterized in that, in the sequential recording process, the photopolymer film (300) is exposed in a third step (206), after exposure of the photopolymer film (300) to incoherent light from a white light source (106) using the first device and the second device.Method according to one of Claims 7 to 11, characterized in that at least one hologram is produced by exposure to the first device (102), and a master hologram is produced by exposure of the at least one hologram to the second device (104), at least one other hologram being produced in a roll-to-roll process on the basis of the master hologram.

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