Method for producing a master hologram for a holographic optical element, holographic optical element, transparent display system and optical sensor system

Abstract

The invention relates to a method (100) for producing a master hologram (3) for a holographic optical element (16), in which a reflective main hologram (1) having at least one optical function is generated, which is further developed into a complex master hologram (3) with superimposed optical functions by joint exposure with a transmissive auxiliary hologram (2) and / or by generating a sub-hologram (15) having at least two optical functions in the reflective main hologram (1). The invention further relates to a holographic optical element (16), a transparent display system (18), and an optical sensor system (19).

Description

The invention relates to a method for producing a master hologram for a holographic optical element. The invention further relates to a holographic optical element, a transparent display system having a holographic optical element and an optical sensor system having a holographic optical element.Prior ArtHolographic optical elements, which can be used, for example, in smart glasses or head-up displays, and methods for producing the same are known from the prior art. Holographic optical elements generally have a hologram for realizing optical functions, for example for realizing shaping or deflection functions for defined beam shaping or beam deflection of a light beam.DE 10 2021 204 872 A1 describes an exposure device and a method for producing a second holographic optical element, in which a first holographic optical element having a first and second partial region and a first photosensitive material are provided. By irradiating the first holographic optical element with first and second light waves of a first and / or second wavelength and partial waves of the first and second light waves generated in this case at the first and second partial region, which interfere in the photosensitive material, a second holographic optical element is generated.Disclosure of the InventionAccording to the features of independent claim 1, a method for producing a master hologram for a holographic optical element is proposed, in which a reflective main hologram having at least one optical function is produced, which is further developed by joint exposure to a transmissive auxiliary hologram and / or by producing a sub-hologram having at least two optical functions in the reflective main hologram to form a complex master hologram having superimposed optical functions.With the proposed method, an optically complex master hologram with a high functional density for a holographic optical element can be provided.According to one embodiment, the method can comprise the following steps:generating a reflective main hologram having a recording wave according to a first recording configuration in a first photosensitive material layer;generating a transmissive auxiliary hologram having a recording wave according to a second recording configuration in a second photosensitive material layer;forming a layer stack with the first photosensitive material layer having the reflective main hologram, the second photosensitive material layer having the transmissive auxiliary hologram and an unexposed third photosensitive material layer; andexposing the layer stack with a reconstruction wave, wherein the reconstruction wave forms a first exposure wavefront transmitting the third photosensitive material layer, and wherein the diffraction properties of the transmissive auxiliary hologram are matched to the reflective main hologram in such a way that a reconstruction of the reflective main hologram takes place by diffraction of the reconstruction wave at the transmissive auxiliary hologram, and a second exposure wavefront is thereby formed, which interferes with the first exposure wavefront in the third photosensitive material layer to form a resulting master hologram.With the proposed embodiment of the method, it is possible to combine the advantages of different types of recording configurations and the advantages associated therewith of the main and auxiliary holograms produced with the different types of recording configurations in one master hologram. With the described method, master holograms for holographic optical elements can thus be produced with high complexity and quality. In this case, there is a high adaptability and freedom of design during the production of the master hologram due to the individual design possibility of the main hologram and of the auxiliary hologram. Furthermore, with the proposed embodiment of the method it is possible to generate a high density of different optical functions in the resulting master hologram. By using the transmissive auxiliary hologram as a Bragg grating for transforming the reconstruction wave, so that the latter can be reproduced from the reflective main hologram, a second exposure wavefront for forming the master hologram can moreover be generated in an efficient manner.A holographic optical element (HOE) is understood in the present case to mean an optical element whose holographic properties can be used for the optics of devices. By means of a master hologram integrated into the holographic optical element, optical functions can be realized, for example shaping or deflection functions for defined beam shaping or beam deflection of a light beam. Holograms for holographic optical elements can in principle be produced by exposure of a holographic recording material. For this purpose, recording wavefronts of the recording waves that are shaped coherently to one another can be brought to interference and the interference pattern that arises in this case can be written into the recording material.The first, second and third photosensitive material layers can each be formed by a photosensitive recording material suitable for recording volume holograms. For example, a photosensitive material layer can be embodied as a photopolymer film. To increase the mechanical stability, the photosensitive material layer can be arranged, for example, on a carrier film, which can comprise, for example, a polyamide or polycarbonate.The reflective main hologram can be a reflective volume hologram. The reflective main hologram can have one, in particular a plurality of optical functions. According to one possible embodiment, it can be provided that the main hologram has a greater optical functional width than the auxiliary hologram. For example, the reflective main hologram can have more optical functions and / or more complex optical functions than the auxiliary hologram. To produce the main hologram as a reflective main hologram, the recording material is exposed in such a way that the recording wavefronts of the recording waves used for exposure come from opposite half spaces with respect to the first photosensitive material layer. Expressed simply, the first photosensitive material layer is exposed from different sides.The transmissive auxiliary hologram can be a transmissive volume hologram. According to one possible embodiment, the transmissive auxiliary hologram can provide one or more additional optical functions which are not covered by the reflective main hologram. For example, the main hologram and the auxiliary hologram can complement one another with regard to different deflection functions. To produce the auxiliary hologram as a transmissive auxiliary hologram, the recording material is exposed in such a way that the recording wavefronts of the recording waves used for exposure come from the same half space with respect to the second photosensitive material layer. Expressed simply, the second photosensitive material layer is exposed from the same side.The first recording configuration and the second recording configuration mentioned can be regarded in particular as recording configurations differing from one another. The main hologram and the auxiliary hologram can therefore be generated in addition to the reflective and transmissive exposure under different optical recording conditions, as will be explained in more detail below with reference to advantageous embodiments.To form a layer stack, the first photosensitive material layer, the second photosensitive material layer and the third photosensitive material layer can be arranged one above the other, such that their layer planes lie on top of one another and run parallel to one another. The sequence of the material layers can be provided in such a way that the third, the second and the first photosensitive material layer follow one another in a propagation direction of the first exposure wavefront of the reconstruction wave.A reconstruction wave can be a recording wave with predefined optical properties for exposure of the layer stack in order to generate a resulting master hologram in the third photosensitive material layer. During the exposure, the reconstruction wave forms a first exposure wavefront which transmits the third photosensitive material layer. The reconstruction wave is diffracted at the auxiliary hologram in accordance with a transmissive Bragg grating formed by the auxiliary hologram and is therefore transformed in accordance with a holographic function of the auxiliary hologram determining the diffraction properties of the auxiliary hologram. The transformed reconstruction wave matches the configuration of the main hologram, so that it reconstructs in reflection and a diffracted second exposure wavefront is generated, which propagates in the direction of the third photosensitive material layer and interferes there with the first exposure wavefront. In other words, a first exposure wavefront is generated by an exposure device, while a further exposure wavefront is generated by successive diffraction at the auxiliary and main hologram, such that the exposure wavefronts enable the master hologram to be formed in the third photosensitive material layer by interference. In principle, it is also conceivable that at least two exposure wavefronts are generated during the diffraction of the reconstruction wave at the main hologram, since a plurality of further exposure wavefronts, in particular superimposed one on the other, can also advantageously be used for interference with the first exposure wavefront.The master hologram formed in the third photosensitive material layer can be further processed, for example fixed and replicated, subsequent to the exposure process. The master hologram can be reproduced with a playback wave which substantially corresponds to the reconstruction wave and can implement the optical functions of the main and auxiliary holograms combined in the master hologram.The method according to the proposed embodiment can be regarded as a multistage recording process with temporally consecutive steps, wherein the production of the main hologram and of the auxiliary hologram can be carried out selectively in parallel or successively with different exposure devices independently of one another.According to one embodiment, the reflective main hologram and the transmissive auxiliary hologram can each be generated at a predefined recording angle between an optical axis of the recording wave and a surface normal of the first or second photosensitive material layer, wherein the recording angle of the second recording configuration deviates from the recording angle of the first recording configuration, in particular is greater than the recording angle of the first recording configuration. As a result, a recording angle can be impressed into the master hologram, which recording angle deviates from the recording angle of the main hologram, in particular is usually not writable jointly with the main hologram by means of a single recording process. Accordingly, with the described embodiment, an expansion of the optical functions of the master hologram is possible with a high freedom of design. The recording angle can be an angle between the respective photosensitive material layer and the optical axis of the recording shaft, which angle is related to a surface normal of the photosensitive material layer for simplification. The reconstruction wave for exposing the third photosensitive material layer can be generated at an exposure angle corresponding to the recording angle of the second recording configuration, so that the auxiliary hologram can convert the provided deflection of the reconstruction wave to the main hologram and the second exposure wavefront can be generated at the main hologram. Accordingly, the resulting master hologram can likewise be reproduced by light irradiation at the exposure angle of the reconstruction wave, wherein in particular flat, i.e. large, exposure angles with respect to the surface normal of the recording material can be favorable, for example, for projection applications with strongly lateral light irradiation, as can be desired, for example, in the case of smart glasses or head-up displays. In addition, a high angular bandwidth of the resulting master hologram can be advantageous for optical diagnostic applications and contribute here to increasing the detection accuracy.According to a development of the embodiment described above, the recording angle of the second recording configuration can be an angle greater than 45° to the surface normal of the second photosensitive material layer. According to advantageous configuration options, the recording angle can be greater than 60° or even greater than 70°. The dimensions refer here to a degree dimension as an angular dimension. By separately providing the auxiliary hologram with a recording angle that can be selected independently of the recording angle of the main hologram, very flat deflection angles can be realized accordingly, which later permit a flat playback angle of the resulting master hologram accordingly.According to one embodiment, the reflective main hologram and the transmissive auxiliary hologram can each be generated with a predefined curvature of a recording wavefront of the recording wave, wherein the curvature of the recording wavefront in accordance with the first recording configuration deviates from a curvature of the recording wavefront in accordance with the second recording configuration. This further increases the design freedom and an achievable complexity of the optical functions of the main and auxiliary holograms and of the resulting master hologram. In particular, the predefined curvature can be subject to complex conditions, for example have different portions with respect to sphere, asphere or coma. Furthermore, an individual synthesis of the recording wavefront is conceivable, for example by means of Zernike polynomial functions.According to one embodiment, the transmissive auxiliary hologram can be generated by means of an analog recording process. In an analog recording process, a hologram is recorded with a widened wavefront in a single exposure step. Associated recording devices can have, for example, conventional optical elements which can be used for beam shaping and / or beam deflection. With an analog recording process, certain optical functions can be made possible or more favorably realized than with digital recording processes such as a wavefront printing process, for example very flat recording angles. If, for example, a digitally recorded main hologram, which is explained below, and an analog recorded auxiliary hologram are combined with one another, the advantages of both recording methods can be efficiently combined with one another and combined in the resulting master hologram. A high functionality diversity of the digitally recorded main hologram can be appropriately specifically supplemented with the analogously recorded auxiliary hologram. The main hologram and the auxiliary hologram as well as the recording processes and recording devices used for recording the main hologram and the auxiliary hologram can be optimized with respect to their respective recording conditions and recording configurations without a compromise solution being required for producing the desired combination of optical functions with a common recording process. In principle, it is not excluded to produce the auxiliary hologram by means of a digital recording process, in particular a wavefront printing process. If, for example, a digitally recorded main hologram and a digitally recorded auxiliary hologram are combined with one another in order to generate the resulting master hologram, a particularly high optical functional complexity can be achieved in the master hologram.According to one embodiment, the optical properties of the reconstruction wave can be matched to a reconstruction of the transmissive auxiliary hologram. Accordingly, the reconstruction wave can be optimized with respect to a reconstruction by the auxiliary hologram. In other words, the optical properties of the reconstruction wave are selected such that it reconstructs the auxiliary hologram ideally. For example, for this purpose, an exposure angle of the reconstruction wave can correspond as exactly as possible to the recording angle of the second recording configuration during the generation of the auxiliary hologram and / or a curvature of the first exposure wavefront formed with the reconstruction wave can correspond as exactly as possible to a curvature of the recording wavefront according to the second recording configuration. By means of a reconstruction wave matched to the auxiliary hologram, an optimized diffraction corresponding to the transmissive Bragg grating of the auxiliary hologram can be achieved, by means of which an optimized formation of a second exposure wavefront during the reflective diffraction of the reconstruction wave on the main hologram is promoted, such that the exposure process of the method is optimized overall.According to one embodiment, the reconstruction wave can be generated in such a way that during the exposure of the layer stack, a reconstruction of the transmissive auxiliary hologram and of the reflective main hologram takes place by means of the reconstruction wave at least approximately under the Bragg condition. In other words, the optical properties of the reconstruction wave can be chosen such that a reconstruction of the main and auxiliary hologram is ensured under conditions close to the so-called Bragg configuration. For example, the wave reconstructed by the auxiliary hologram by means of the reconstruction wave can be matched to the recording wave of the first recording configuration of the main hologram, for example with regard to the wavelength, collimation, recording angle and / or curvature of the recording wavefront. As a result, the diffracted wavefront of the reconstructed auxiliary hologram can generate a wavefront matching the main hologram, with the result that the latter is reconstructed in reflection and a diffracted exposure wavefront is produced which propagates in the direction of the unexposed third photosensitive material layer. By at least approximately satisfying the Bragg condition of the Bragg grating underlying the main hologram, the generation of the exposure wavefront can be optimized by diffraction at the auxiliary and main hologram, such that a resulting master hologram can be produced with high quality.According to one embodiment, a plurality of different transmissive auxiliary holograms and / or a plurality of different reflective main holograms can be generated and a combination of a transmissive auxiliary hologram and a reflective main hologram can be selected for the resulting master hologram as a function of predefined criteria in order to form the layer stack with the first material layer having the selected reflective main hologram, the second material layer having the selected transmissive auxiliary hologram and an unexposed third photosensitive material layer. As a result, a production process for master holograms can be made more flexible and the production of different holograms for holographic optical elements can be simplified and accelerated. By the respective provision and selection of suitable main and auxiliary holograms, an increased achievable variety of realizable hologram functions can be made possible. The generated transmissive auxiliary holograms and / or the generated reflective main holograms can accordingly form a type of modular system, by means of which the individually desired properties of the master hologram can be composed during the exposure process. For example, different transmissive auxiliary holograms can be provided which realize deflection functions differing from one another with different solid angles. For example, different reflective main holograms with different optical function combinations can be provided. When generating, selecting and combining the selected main and auxiliary holograms, it is to be noted in particular that the diffraction properties of the auxiliary hologram are matched to the main hologram in such a way that a reconstruction of the main hologram can take place by diffraction of the reconstruction wave at the transmissive auxiliary hologram and a second exposure wavefront can thereby be formed which can interfere with the first exposure wavefront in the third photosensitive material layer to form a resulting master hologram.In principle, it is also conceivable to generate only one reflective main hologram and a plurality of transmissive auxiliary holograms, wherein a selection of a transmissive auxiliary hologram for the layer stack is then made among the plurality of transmissive auxiliary holograms. It is likewise also conceivable to generate only one transmissive auxiliary hologram and a plurality of reflective main holograms, wherein a selection of a reflective main hologram for the layer stack is then made among the plurality of reflective main holograms.According to one embodiment, the method can additionally have the following further steps:generating a second transmissive auxiliary hologram having a recording wave according to a third recording configuration in a fourth photosensitive material layer;forming a layer stack with the first material layer having the reflective main hologram, the fourth material layer having the second transmissive auxiliary hologram and the third photosensitive material layer having the master hologram; andexposing the layer stack with the reconstruction wave, wherein the reconstruction wave forms a first exposure wavefront transmitting the third photosensitive material layer, and wherein the diffraction properties of the second transmissive auxiliary hologram are matched to the main hologram in such a way that a reconstruction of the reflective main hologram takes place by diffraction of the reconstruction wave at the transmissive auxiliary hologram, and a second exposure wavefront is thereby formed, which interferes with the first exposure wavefront in the third photosensitive material layer in order to expand the master hologram.The optical functional density of the master hologram can thereby be further increased. In principle, it is conceivable to repeat the steps described above in any desired number using different transmissive auxiliary holograms in order to supplement or refine the optical functions contained in the master hologram incrementally. In other words, further functions can be gradually exposed into the master hologram by replacing the transmissive auxiliary hologram in the layer stack with other transmissive auxiliary holograms. For example, the different transmissive auxiliary holograms can realize deflection functions differing from one another with different solid angles. In principle, it is not excluded, alternatively or in addition to the exchange of the transmissive auxiliary hologram, to carry out an exchange of the reflective main hologram for a further reflective main hologram and to carry out an exposure again in order to expand the master hologram in an analogous manner in accordance with the steps described.According to one embodiment, the first and / or the second recording configuration can have a recording angle adaptation as a function of an intended wavelength difference between the recording wave and a playback wave of the master hologram and / or as a function of a known shrinkage compensation. This allows additional optimization of the auxiliary hologram and / or of the main histogram for improving the playback properties of the master hologram. For example, a specific slight adaptation of a recording angle of the recording configuration can compensate for a wavelength difference between the recording wave and the intended playback wave. The angular and wavelength bandwidth of the holograms can be increased in a targeted manner, in particular for a specific target value of the diffraction efficiency. Shrinkage compensation refers to a condition for a technical shrinkage of the photosensitive material layers depending on the selected recording material.According to one embodiment, the first photosensitive material layer and / or the second photosensitive material layer and / or the third photosensitive material layer can be formed as a silver halide film or dichromate-gelatin film. This also applies to optionally used further photosensitive material layers, for example to a fourth photosensitive material layer for exposing a further auxiliary hologram or main hologram into the master hologram. Silver halide films or dichromate-gelatin films make it possible to produce particularly high-resolution holograms with a low noise content, and so a high quality and complexity of the resulting master hologram can be implemented.According to one embodiment, after the exposure of the layer stack to the reconstruction wave to form the resulting or extended master hologram, the master hologram can be fixed by an exposure process using an incoherent light source. As a result, the master hologram can be fixed in a simple manner and a high quality of the master hologram can be ensured. The incoherent light source may be, for example, a white light source, a UV light source or a UV-near light source. By exposure to the incoherent light source, the third photosensitive material layer with the resulting master hologram is bleached and brought into a stationary state. For example, in the case of a photopolymer film, the bleaching process causes crosslinking of the polymer and, as a result, fixing of the written holographic structure. In addition, the transparency properties of the master hologram can be controlled with respect to a low amount of scattered light with the bleaching process. In a multi-step exposure process for expanding the master hologram by exchanging an auxiliary hologram or main hologram with subsequent re-exposure, as explained with reference to the embodiment described further above, it can be provided in particular that the described exposure process with the incoherent light source for fixing takes place only after generation of a final master hologram, i.e. no further subsequent exposure of a further auxiliary hologram or main hologram is provided any longer.According to one embodiment, the reflective main hologram can be designed as a complex main hologram having a plurality of superimposed holographic functions and / or the transmissive auxiliary hologram can be designed as a complex auxiliary hologram having a plurality of superimposed holographic functions. This allows the complexity of the master hologram produced to be further increased. For example, in the complex main hologram and / or in the complex auxiliary hologram, a plurality of holographic solid angle deflection functions can be superimposed on one another, which deflection functions realize mutually deviating deflection functions with different solid angles. Such complex holograms can be produced, for example, with a high quality by simultaneous exposure with a correspondingly designed exposure device or by sequential exposure with different recording configurations. According to one embodiment, the reflective main hologram can be generated by means of a wavefront printing process, in particular when the reflective main hologram is formed as a complex main hologram having a plurality of superimposed holographic functions, in which at least one recording wavefront of the recording wave is modulated by a modulation device. The modulation device can have, for example, a spatial light modulator (SLM), an adaptive phase plate, a deformable mirror, a micromirror actuator (DMD) and / or a diffractive optical element (DOE). By means of the modulation device, a modulation can be impressed on the recording wave, which modulation represents an optical function, for example by modulation of a laser beam forming the recording wave. Wavefront printing processes are also referred to as digital recording processes, since, when holograms are produced by means of wavefront printing processes, individual sub-holograms in a matrix structure are successively exposed by a sequential exposure method by a correspondingly configured recording apparatus. The size of a sub-hologram may vary between 50 μm and 1 mm, according to a non-limiting embodiment. The sub-holograms can have individual optical functions or contribute together to a superordinate optical function by a respective function component. The respective optical function of a sub-hologram can be defined by a corresponding individual modulation of the recording wavefront, such that different optical functions can be realized during the sequential exposure during the wavefront printing process by a temporally varying modulation of the recording wavefront from sub-hologram to sub-hologram. A main hologram with a high optical complexity, functionality diversity and freedom of design can thus be produced. In particular, by producing the main hologram using a wavefront printing process, a main proportion of the desired optical functionalities of the holographic optical element to be produced can already be converted, which can be added in a targeted manner during the production of the auxiliary hologram. In principle, however, it is not excluded to produce the main hologram alternatively by means of an analog recording process explained in more detail below.By generating a reflective main hologram by means of a wavefront printing process, a complex master hologram with superimposed optical functions can be generated even without exposure of an additional transmissive auxiliary hologram. Due to the sub-holograms of the main hologram that can be individually provided with optical functions by a wavefront printing process, which sub-holograms can also be produced with a plurality of optical functions superimposed on one another, in particular within the scope of the wavefront printing process, a high functional density and optical complexity of the resulting master hologram can already be achieved with such a reflective main hologram.According to a further development of the embodiment described above, at least two recording wavefronts of the recording wave can each be modulated independently of one another by a modulation device. For example, the recording wavefronts can each be individually modulated by a separate spatial light modulator or another of the mentioned modulation devices. This allows precise and versatile implementation of complex optical functions in the main hologram with a high freedom of design. In particular, a superimposition of optical functions is made possible for each individual sub-hologram.According to one embodiment, at least one sub-hologram having a collimating optical function can be generated in the reflective main hologram. As a result, a master hologram for a holographic optical element can be provided, by means of which it is possible to collimate light incident into the holographic optical element.According to a development, at least one sub-hologram having a converging main function and a collimating auxiliary function can be generated in the reflective main hologram. As a result, a plurality of optical functions can be superimposed in the sub-hologram and a complex master hologram can be formed by means of the reflective main hologram. In particular, a plurality of sub-holograms can be generated in the reflective main hologram, each sub-hologram having a converging main function and a collimating auxiliary function. The reflective main hologram can be generated in particular by a wavefront printing process, in particular with recording wavefronts modulated independently of one another.In the above-described embodiment, the main hologram may satisfy a so-called global point-to-point transformation as a global function that may correspond to the converging main function. In this case, the global function of the reflective main hologram can correspond to a convergent wavefront which is generated by diffraction of a reconstruction wave at the Bragg structures of the sub-holograms. For example, the reconstruction wave can represent a divergent optical function. The reconstruction wave can be diffracted at the individual sub-holograms, wherein a local individual beam deflected by the individual sub-hologram does not converge according to the global function, but rather is deflected in a collimated manner according to the collimating auxiliary function. Thus, each sub-hologram can combine two optical functions, a first optical function redirecting the incident light beam according to the auxiliary collimating function, a second optical function introducing a spherical contribution and forming a convergent wave from the divergent reconstruction wave according to the main convergent function.Due to the generation of the master hologram in a single photosensitive material layer, the master hologram can be duplicated in any number of pieces in a simple manner. In particular, according to an embodiment, the master hologram may be replicated in a continuous series manufacturing process. The holographic element produced with the master hologram is therefore suitable for continuous reproduction in large numbers. For example, the master hologram can be continuously replicated by means of a roll-to-roll process.The invention also relates to a holographic optical element, having a master hologram formed by superimposed reconstruction of a reflective main hologram and a transmissive auxiliary hologram and / or by generating a sub-hologram having at least two optical functions in a reflective main hologram. This provides a holographic optical element with a high optical complexity and quality. For example, by skillful combination of recording configurations of the reflective main hologram and the transmissive auxiliary hologram, a holographic optical element having a high optical functionality and special additional optical properties, for example a very flat playback angle or a combination of a converging optical function and a collimating optical function, can be provided compared to conventional holographic optical elements. In this case, for example, an interference pattern resulting from a reconstruction of the main and auxiliary holograms can be written into an individual photosensitive material layer, wherein the optical functions of the main and auxiliary holograms can be distinguished in the master hologram by means of diffraction experiments or microscopic examination. The master hologram can be, for example, a projection hologram or a coupling hologram with extreme angles, which can couple light into and out of a waveguide under total reflection. The holographic optical element can be incorporated into a spectacle lens, for example, for use in smart glasses. The holographic optical element can in particular have a master hologram which is produced by the method described above.According to one embodiment, the holographic optical element can be designed as an optical combiner. Thus, a plurality of optical functions may be realized in the master hologram, so that a holographic optical element having a high function density or variety is provided.According to one embodiment, the reflective main hologram can be a wavefront-printed main hologram and the transmissive auxiliary hologram can be an analog auxiliary hologram. A wavefront printed main hologram is a main hologram produced by means of a wavefront printing process. Wavefront printing processes have been explained in connection with the method described above. In particular, the main hologram can be a main hologram which is produced with a wavefront printing process in which at least one recording wavefront of the recording wave is modulated by a modulation device.According to one embodiment, the reflective main hologram can have at least one sub-hologram with a collimating optical function. As a result, a master hologram for a holographic optical element can be provided, by means of which it is possible to collimate light incident into the holographic optical element. In particular, the reflective main hologram can have a plurality of sub-holograms, each having a collimating optical function.According to a further development, the reflective main hologram can have at least one sub-hologram with a converging main function and a collimating auxiliary function. As a result, a plurality of optical functions can be superimposed in the sub-hologram and a complex master hologram can be provided by means of the reflective main hologram. In particular, a plurality of sub-holograms can be formed in the reflective main hologram, each of which sub-holograms has a converging main function and a collimating auxiliary function.According to one embodiment, the transmissive auxiliary hologram can be an analog auxiliary hologram. An analog auxiliary hologram is an auxiliary hologram produced by an analog recording process. Analogous recording processes have been explained in connection with the method described above. For example, by combining a wavefront-printed main hologram with an analog auxiliary hologram, a combined use of the advantages of the two explained recording methods and advantages of the main and auxiliary holograms resulting therefrom is possible for the resulting master hologram. For example, deflection functions with very flat deflection angles can be realized with an analog auxiliary hologram, which deflection functions cannot be generated with a wavefront-printed main hologram. At the same time, the wavefront-printed main hologram can provide a hologram having a high optical range of function, which hologram can be transferred to the master hologram by exposure to light.The invention also relates to a transparent display system having a holographic optical element according to one of the features described above. The transparent display system can be, for example, smart glasses or a head-up display. Due to a high complexity and quality of the master hologram incorporated into the holographic optical element, as is achieved in the present case, such display systems can be further technically optimized. For example, complex master holograms can be used with deflection functions which realize very flat deflection angles.The invention also relates to a transparent display system having a holographic optical element and a transparent microlens array having a collimating optical function. With such a display system, it is also possible to realize a complex optical function in conjunction with a holographic optical element. The transparent microlens array can be, for example, a two-dimensional microlens array matched to a wavelength of a light source used. The transparent microlens array can be integrated into a carrier layer, for example a photopolymer, of the holographic optical element. The transparent microlens array can be configured to collimate an individual beam of the holographic optical element, which beam can have, for example, an analog recorded main hologram. In this case, individual microlenses of the transparent microlens array can be regarded as optical subcomponents, analogously to the above-described sub-holograms of a wavefront-printed main hologram, which optical subcomponents can enable individual configuration and superimposition of optical functions.The invention also relates to an optical sensor system, in particular a laboratory-diagnostic optical sensor system, having a holographic optical element according to one of the features described above. The optical sensor system can be configured, for example, for examining biological samples. The optical sensor system can be applicable, for example, for fluorescence-based diagnostics. Holograms are used in particular in optical excitation and detection paths of the sensor system in such optical sensor systems. If the optical sensor system has a holographic optical element according to one of the features described above, a high functionality variety of spectral functions, in particular with a plurality of different deflection angles, can be provided with the holographic optical element. This makes it possible to achieve an advantageous increase in the detection accuracy and the detection bandwidth.In the context of this application, the words "a / an", unless expressly defined otherwise, are not to be understood as a numerical word, but rather as an indeterminate article having the word sense of "at least one / one".The invention permits various embodiments and is explained in more detail below with reference to an exemplary embodiment with the accompanying drawings. They show in schematic form: FIG. 1 shows a recording principle for generating a reflective main hologram according to an exemplary embodiment; FIG. 2 shows a recording principle for producing a transmissive auxiliary hologram according to an exemplary embodiment; FIG. 3 shows an exposure principle for producing a resulting master hologram by means of the main hologram and the auxiliary hologram in a layer stack according to an exemplary embodiment; FIG. 4 shows a master hologram replicated from the master hologram resulting from FIG. 3; FIG. 5 shows a further exemplary embodiment of a master hologram formed from a main hologram; FIG. 6 shows a transparent display system having a holographic optical element having a master hologram; FIG. 7 shows an optical sensor system having a holographic optical element having a master hologram; FIG. 8 shows a schematic method sequence of a method for producing a master hologram for a holographic optical element according to an exemplary embodiment.FIG. 1 shows a schematic schematic diagram of a recording principle for generating a reflective main hologram 1 according to an exemplary embodiment. For this purpose, a first photosensitive material layer 5 is provided and exposed to a recording wave 4 aaccording to a first recording configuration. The recording wave 4 aaccording to the first recording configuration has a propagation direction with an optical axis 11, wherein the optical axis 11 according to the exemplary embodiment shown coincides with a surface normal 12 of the first photosensitive material layer 5, such that a recording angle α 1 between the optical axis 11 and the surface normal 12 is present as a zero angle. The recording wave 4 acan furthermore be described by a recording wavefront 13 which has a predefined curvature k 1 according to the first recording configuration. According to the illustrated exemplary embodiment, the reflective main hologram 1 is generated by means of a wavefront printing process, in which at least one recording wavefront 13 of the recording wave 4 ais modulated by at least one modulation device, not illustrated in more detail. The wavefront printing process can form individual sub-holograms 15 having individual optical functions as a function of the respective modulation of the recording wavefront 13, which sub-holograms jointly form a main hologram 1 having a plurality of optical functions or contribute proportionally to a superordinate optical function of the main hologram 1. The optical function of each sub-hologram 15 is locally written into the first photosensitive material layer 5 by means of the recording wavefront 13. By means of an auxiliary wave 20, a second wavefront is provided, which interferes together with the recording wave 4 ain the first photosensitive material layer 5, such that a holographic grating is formed. As schematically illustrated in FIG. 1, a planar wave can be selected in particular for such an auxiliary wave 20, since this can again be easily generated for the later reconstruction of the reflective main hologram 1.FIG. 2 shows a schematic schematic diagram of a recording principle for producing a transmissive auxiliary hologram 2 according to an exemplary embodiment. For this purpose, a second photosensitive material layer 6 is provided and exposed to a recording wave 4 bin accordance with a second recording configuration. The recording wave 4 bin accordance with the second recording configuration has a propagation direction with an optical axis 11 which, with the surface normal 12 of the second photosensitive material layer 6, spans a recording angle α 2 which deviates from the recording angle α 1 in accordance with the first recording configuration shown in FIG. 1. In particular, it can be seen that the recording angle α 2 according to the second recording configuration is greater than the recording angle α 1 according to the first recording configuration. According to the exemplary embodiment shown in FIG. 2, the recording angle α 2 is greater than 45°. The recording wave 4 bmay be further described by a recording wavefront 13 having a predefined curvature k 2 according to the second recording configuration, wherein the curvature k 2 according to the second recording configuration may deviate from the curvature k 1 according to the first recording configuration. According to the illustrated exemplary embodiment, the transmissive auxiliary hologram 2 is produced by means of an analog recording process. Accordingly, the auxiliary hologram 2 is recorded in a single exposure step with a widened recording wavefront 13. As a result, it is possible in a simple manner with available exposure apparatuses to realize a recording angle α 2 of greater than 45°. The optical function of the transmissive auxiliary hologram 2 is written into the second photosensitive material layer 6 by means of the recording wavefront 13 by a single exposure step and can supplement the optical functions of the main hologram 1. By means of an auxiliary wave 20, a second wavefront is provided, which interferes together with the recording wave 4 bin the second photosensitive material layer 6, such that a holographic grating is formed. As schematically illustrated in FIG. 2, a planar wave can be selected in particular for such an auxiliary wave 20, since this can again be easily generated for the later reconstruction of the transmissive auxiliary hologram 2.FIG. 3 shows the formation of a layer stack 8, wherein the first photosensitive material layer 5 having the reflective main hologram 1, the second photosensitive material layer 6 having the transmissive auxiliary hologram 2 and an unexposed third photosensitive material layer 7 are arranged one above the other in the layer stack 8. The layer stack 8 is then exposed to a reconstruction wave 9. The reconstruction wave 9 forms a first exposure wavefront 10 aand transmits the third photosensitive material layer. The diffraction properties of the transmissive auxiliary hologram 2 are matched to the reflective main hologram 1 in such a way that the reflective main hologram 1 is reconstructed by diffraction of the reconstruction wave 9 at the transmissive auxiliary hologram 2. As a result, second exposure wavefronts 10 bare formed in reflection, which propagate in the direction of the third photosensitive material layer 7 and interfere there with the first exposure wavefront 10 a. Thus, a resultant master hologram 3 having the optical functions of the main hologram 1 and the auxiliary hologram 2 is written into the third photosensitive material layer 7. The resulting master hologram 3 can then be fixed, for example by an exposure process using an incoherent light source, and replicated as a final master hologram 3.FIG. 4 shows such a final replicated master hologram 3, to which a playback wave 14 is applied. As can be seen from FIG. 4, thanks to the optical function of the auxiliary hologram 2 written in addition to the holographic function of the main hologram with the master hologram 3, a large deflection angle β can be realized for deflecting the incident light beam, wherein at the same time the functionality of the main hologram 1 can be implemented with the master hologram 3.FIG. 5 shows a simplified schematic diagram of a further exemplary embodiment of a master hologram 3 formed from a reflective main hologram 1. the main hologram 1 in this case has, as indicated schematically, a plurality of sub-holograms 15 having a converging main function 21 and a collimating auxiliary function 22. In this case, the main hologram 1 can fulfil a so-called global point-to-point transformation as a global function which can correspond to the converging main function 21. In this case, the global function of the reflective main hologram 1 can correspond to a convergent wavefront which is generated by diffraction of a reconstruction wave 9 at the Bragg structures of the sub-holograms 15. For example, the reconstruction wave 9 can represent a divergent optical function. The reconstruction wave 9 can be diffracted at the individual sub-holograms 15, wherein a local individual beam deflected by the individual sub-hologram 15 does not converge according to the global function but rather is deflected in a collimated manner according to the collimating auxiliary function 22. Accordingly, each sub-hologram 15 can combine two optical functions, wherein a first optical function deflects the incident light beam according to the collimating auxiliary function 22, while a second optical function introduces a spherical contribution and forms a convergent wave according to the convergent main function 21 from the divergent reconstruction wave 9. By such a configuration of the Bragg structures on the sub-holograms 15, for example, any desired region 23 independent of a global hologram function of the main hologram 1 can be illuminated.FIG. 6 shows a schematic diagram of a transparent display system 18 having a holographic optical element 16, which has a master hologram 3 according to one of the features described above, for example according to FIG. 4. The transparent display system 18 can be, for example, a head-up display or smart glasses.FIG. 7 shows a schematic schematic diagram of an optical sensor system 19 having a holographic optical element 16 which has a master hologram 3 according to one of the features described above, for example according to FIG. 4. The optical sensor system 19 can be, for example, a fluorescence-based diagnostic system.FIG. 8 shows method steps of a method 100 for producing a master hologram 3 for a holographic optical element 16 according to an exemplary embodiment with reference to a schematic flow diagram. Accordingly, in a first step 110, a reflective main hologram 1 having a recording wave 4 acan be generated in accordance with a first recording configuration in a first photosensitive material layer 5, as is shown on the basis of an exemplary embodiment in FIG. 1. In a second step 120, a transmissive auxiliary hologram 2 having a recording wave 4 bcan be produced in accordance with a second recording configuration in a second photosensitive material layer 6, as is shown with reference to an exemplary embodiment in FIG. 2. In a third step 130, a layer stack 8 can be formed with the first material layer 5 having the reflective main hologram 1, the second material layer 6 having the transmissive auxiliary hologram 2 and an unexposed third photosensitive material layer 7. Subsequently, the layer stack 8 can be exposed with a reconstruction wave 9, wherein the reconstruction wave 9 forms a first exposure wavefront 10 athat transmits the third photosensitive material layer 7, and wherein the diffraction properties of the transmissive auxiliary hologram 2 are matched to the reflective main hologram 1 in such a way that the reflective main hologram 1 is reconstructed by diffraction of the reconstruction wave 9 at the transmissive auxiliary hologram 2, and a second exposure wavefront 10 bis thereby formed, which interferes with the first exposure wavefront 10 ain the third photosensitive material layer 7 to form a resulting master hologram 3. These steps 130 and 140 have been explained in addition by way of example with reference to FIG. 3.With the described method 100, the holographic optical element 16 and the systems equipped therewith, it is possible to form a holographic optical element 16 with a high optical functional density. For example, the advantages of different recording configurations of holograms can be combined in a master hologram 3. In this case, a master hologram 3 having a high complexity and quality can be produced. The method 100 according to the exemplary embodiment shown is associated with a high freedom of design and adaptability, in particular also by the individual design possibility of the main hologram 1 and of the auxiliary hologram 2.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2021 204 872 A1

[0003]

Claims

Method (100) for producing a master hologram (3) for a holographic optical element (16), in which a reflective main hologram (1) having at least one optical function is produced, which is further developed by joint exposure to a transmissive auxiliary hologram (2) and / or by producing a sub-hologram (15) having at least two optical functions in the reflective main hologram (1) to form a complex master hologram (3) having superimposed optical functions.Method (100) according to Claim 1, comprising the following steps: - generating a reflective main hologram (1) with a recording wave (4a) according to a first recording configuration in a first photosensitive material layer (5) (110); - generating a transmissive auxiliary hologram (2) with a recording wave (4b) according to a second recording configuration in a second photosensitive material layer (6) (120); - forming a layer stack (8) with the first material layer (5) comprising the reflective main hologram (1), the second material layer (6) comprising the transmissive auxiliary hologram (2) and an unexposed third photosensitive material layer (7) (130); and - exposing the layer stack (8) with a reconstruction wave (9), wherein the reconstruction wave (9) forms a first exposure wavefront (10a) transmitting the third photosensitive material layer (7) and wherein the diffraction properties of the transmissive auxiliary hologram (2) are matched to the reflective main hologram (1) in such a way that a reconstruction of the reflective main hologram (1) takes place by diffraction of the reconstruction wave (9) at the transmissive auxiliary hologram (2) and a second exposure wavefront (10b) is thereby formed, which interferes (140) with the first exposure wavefront (10a) in the third photosensitive material layer (7) to form a resulting master hologram (3).Method (100) according to Claim 2, wherein the reflective main hologram (1) and the transmissive auxiliary hologram (2) are each produced at a predefined recording angle (α 1, α 2) between an optical axis (11) of the recording wave (4a, 4b) and a surface normal (12) of the first or second photosensitive material layer (5, 6), and wherein the recording angle (α 2) of the second recording configuration deviates from the recording angle (α 1) of the first recording configuration, in particular is greater than the recording angle (α 1) of the first recording configuration.Method (100) according to claim 3, wherein the recording angle (α 2) of the second recording configuration is an angle greater than 45° to the surface normal (12) of the second photosensitive material layer (6).Method (100) according to one of Claims 2 to 4, wherein the production of the reflective main hologram (1) and of the transmissive auxiliary hologram (2) is in each case effected with a predefined curvature (k 1, k 2) of a recording wavefront (13) of the recording wave (4a, 4b), and wherein the curvature (k 1) of the recording wavefront (13) according to the first recording configuration deviates from a curvature (k 2) of the recording wavefront (13) according to the second recording configuration.Method (100) according to one of Claims 2 to 5, wherein the transmissive auxiliary hologram (2) is produced by means of an analog recording process.Method (100) according to one of Claims 2 to 6, wherein the optical properties of the reconstruction wave (9) are matched to a reconstruction of the transmissive auxiliary hologram (2).Method (100) according to one of Claims 2 to 7, wherein the reconstruction wave (9) is generated in such a way that during the exposure of the layer stack (8), a reconstruction of the transmissive auxiliary hologram (2) and of the reflective main hologram (1) by means of the reconstruction wave (9) takes place at least approximately under the Bragg condition.Method (100) according to one of Claims 2 to 8, wherein a plurality of different transmissive auxiliary holograms (2) and / or a plurality of different reflective main holograms (1) are generated and, as a function of predefined criteria, a combination of a transmissive auxiliary hologram (2) and a reflective main hologram (1) is selected for the resulting master hologram (3) in order to form the layer stack (8) with the first material layer (5) having the selected reflective main hologram (1), the second material layer (6) having the selected transmissive auxiliary hologram (2) and an unexposed third photosensitive material layer (7).Method (100) according to one of Claims 2 to 9, additionally having the steps: - generating a second transmissive auxiliary hologram (2) with a recording wave (13) according to a third recording configuration in a fourth photosensitive material layer; - forming a layer stack (8) with the first material layer (5) having the reflective main hologram (1), the fourth material layer having the second transmissive auxiliary hologram (2) and the third photosensitive material layer (7) having the master hologram (3); and - exposing the layer stack (8) with the reconstruction wave (9), wherein the reconstruction wave (9) forms a first exposure wavefront (10a) transmitting the third photosensitive material layer (7) and wherein the diffraction properties of the second transmissive auxiliary hologram (2) are matched to the main hologram (1) in such a way that a reconstruction of the reflective main hologram (1) takes place by diffraction of the reconstruction wave (9) at the transmissive auxiliary hologram (2) and a second exposure wavefront (10b) is thereby formed, which interferes with the first exposure wavefront (10a) in the third photosensitive material layer (7) for expanding the master hologram (3).Method (100) according to one of Claims 2 to 10, wherein the first and / or the second recording configuration has a recording angle adaptation as a function of a provided wavelength difference between the recording wave (4a, 4b) and a playback wave (14) of the master hologram (3) and / or as a function of known shrinkage compensation.Method (100) according to one of Claims 2 to 11, wherein the first photosensitive material layer (5) and / or the second photosensitive material layer (6) and / or the third photosensitive material layer (7) is formed as a silver halide film or dichromate-gelatin film.Method (100) according to one of Claims 2 to 12, wherein, after the exposure of the layer stack (8) to the reconstruction wave (9) in order to form the resulting or extended master hologram (3), the master hologram (3) is fixed by an exposure process using an incoherent light source.Method (100) according to one of the preceding claims, wherein the reflective main hologram (1) is designed as a complex main hologram (1) with a plurality of superimposed holographic functions and / or the transmissive auxiliary hologram (2) is designed as a complex auxiliary hologram (2) with a plurality of superimposed holographic functions.Method (100) according to one of the preceding claims, wherein the reflective main hologram (1) is generated by means of a wavefront printing process, in which at least one recording wavefront (13) of the recording wave (4a) is modulated by at least one modulation device.Method (100) according to claim 15, wherein at least two recording wavefronts (13) of the recording wave (4a) are each modulated independently of one another by a modulation device.Method (100) according to either of Claims 15 and 16, wherein at least one sub-hologram (15) having a collimating optical function is generated in the reflective main hologram (1).Method according to claim 17, wherein at least one sub-hologram (15) with a converging main function (21) and a collimating auxiliary function (22) is generated in the reflective main hologram (1).Method (100) according to one of the preceding claims, wherein the master hologram (3) is replicated in a continuous series production process.Holographic optical element (16), having a master hologram (3) formed by superimposed reconstruction of a reflective main hologram (1) and of a transmissive auxiliary hologram (2) and / or by generating a sub-hologram (15) having at least two optical functions in a reflective main hologram (1).Holographic optical element (16) according to Claim 20, wherein the holographic optical element (16) is designed as an optical combiner.Holographic optical element (16) according to claim 20 or 21, wherein the reflective main hologram (1) is a wavefront-printed main hologram (1).Holographic optical element (16) according to claim 22, wherein the reflective main hologram (1) comprises at least one sub-hologram (15) having a collimating optical function.Holographic optical element (16) according to Claim 23, wherein the reflective main hologram (1) has at least one sub-hologram (15) having a converging main function (21) and an auxiliary collimating function (22).Holographic optical element (16) according to one of Claims 20 to 24, wherein the transmissive auxiliary hologram (2) is an analog auxiliary hologram (2).Holographic optical element (16) according to one of Claims 20 to 25, wherein the master hologram (3) is produced by means of a method (100) according to one of Claims 1 to 19.A transparent display system (18) comprising a holographic optical element (16) according to any of claims 20 to 26.A transparent display system (18) comprising a holographic optical element (16) according to any of claims 20 to 26 and a transparent micro-lens array having a collimating optical function.Optical sensor system (19), in particular laboratory-diagnostic optical sensor system (19), having a holographic optical element (16) according to one of Claims 20 to 26.

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