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), wherein a reflective main hologram (1) having at least one optical function is produced, which is further developed into a complex master hologram (3) having superimposed optical functions by way of joint exposure with 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). The invention furthermore relates to a holographic optical element (16), a transparent display system (18) and an optical sensor system (19).

Description

[0001] Method for producing a master hologram for a holographic optical element, holographic optical element, transparent display system and optical sensor system

[0002] 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 with a holographic optical element, and an optical sensor system with a holographic optical element.

[0003] State of the art

[0004] Holographic optical elements, which can be used, for example, in data glasses or head-up displays, and methods for their production are known from the prior art. Holographic optical elements typically have a hologram for implementing optical functions, for example, for implementing shaping or deflecting functions for the defined beam shaping or beam deflection of a light beam.

[0005] 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. A second holographic optical element is produced by irradiating the first holographic optical element with first and second light waves of a first and / or second wavelength, and thereby generating partial waves of the first and second light waves at the first and second partial regions, which interfere in the photosensitive material. Disclosure of the Invention

[0006] According 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 generated, which is further developed into a complex master hologram with superimposed optical functions by joint exposure with a transmissive auxiliary hologram and / or by generating a sub-hologram having at least two optical functions in the reflective main hologram.

[0007] The proposed method can provide an optically complex master hologram with a high functional density for a holographic optical element.

[0008] According to one embodiment, the method may comprise the following steps:

[0009] - generating a reflective main hologram with a recording wave according to a first recording configuration in a first photosensitive material layer;

[0010] - generating a transmissive auxiliary hologram with a recording wave according to a second recording configuration in a second photosensitive material layer;

[0011] - forming a layer stack comprising the first photosensitive material layer comprising the reflective main hologram, the second photosensitive material layer comprising the transmissive auxiliary hologram, and an unexposed third photosensitive material layer; and

[0012] - exposing the layer stack to 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 diffraction of the reconstruction wave at the transmissive auxiliary hologram results in reconstruction of the reflective main hologram, thereby forming a second exposure wavefront which interferes with the first exposure wavefront in the third photosensitive material layer to form a resulting master hologram.

[0013] The proposed embodiment of the method makes it possible to combine the advantages of various recording configurations and the associated advantages of the main and auxiliary holograms generated with the various recording configurations in a master hologram. The described method thus enables master holograms for holographic optical elements with high complexity and quality to be generated. This allows for a high degree of adaptability and design freedom in the production of the master hologram due to the individual design options for the main hologram and the auxiliary hologram. Furthermore, the proposed embodiment of the method makes it 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 to transform the reconstruction wave so that it can be played back by the reflective main hologram, a second exposure wavefront can be efficiently generated to form the master hologram.

[0014] A holographic optical element (HOE) is understood here to be an optical element whose holographic properties can be used for the optics of devices. Using a master hologram integrated into the holographic optical element, optical functions can be realized, for example shaping or deflecting functions for the defined beam shaping or beam deflection of a light beam. Holograms for holographic optical elements can generally be produced by exposing a holographic recording material. For this purpose, coherently shaped recording wavefronts of the recording waves can be caused to interfere with one another, and the resulting interference pattern 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 mechanical stability, the photosensitive material layer can be arranged on a carrier film, which can be made of, for example, a polyamide or polycarbonate.

[0015] The reflective main hologram can be a reflective volume hologram. The reflective main hologram can have one, in particular multiple, optical functions. According to one possible embodiment, the main hologram can have a greater range of optical functions 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 such that the recording wavefronts of the recording waves used for exposure come from opposite half-spaces relative to the first photosensitive material layer. In simple terms, the first photosensitive material layer is exposed from different sides.

[0016] 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 not covered by the reflective main hologram. For example, the main hologram and the auxiliary hologram can complement each other with regard to different deflection functions. To produce the auxiliary hologram as a transmissive auxiliary hologram, the recording material is exposed such that the recording wavefronts of the recording waves used for exposure originate from the same half-space relative to the second photosensitive material layer. In simple terms, the second photosensitive material layer is exposed from the same side.

[0017] The aforementioned first recording configuration and the aforementioned second recording configuration can in particular be considered as different recording configurations. The main hologram and the auxiliary hologram can therefore be generated under different optical recording conditions in addition to the reflective and transmissive exposure, as will be explained in more detail below with reference to advantageous embodiments.

[0018] 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 so that their layer planes lie on top of one another and run parallel to one another. The sequence of the material layers can be arranged such that the third, second, and first photosensitive material layers follow one another in a propagation direction of the first exposure wavefront of the reconstruction wave.

[0019] A reconstruction wave can be a recording wave with predetermined optical properties for exposing the layer stack to generate a resulting master hologram in the third photosensitive material layer. During exposure, the reconstruction wave forms a first exposure wavefront that the third photosensitive material layer transmits. At the auxiliary hologram, the reconstruction wave is diffracted according to a transmissive Bragg grating formed by the auxiliary hologram and thus reshaped according to a holographic function of the auxiliary hologram that determines the diffraction properties of the auxiliary hologram. The reshaped reconstruction wave matches the configuration of the main hologram, so that it is reconstructed in reflection, and a diffracted second exposure wavefront is generated, which propagates toward 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 holograms, so that the exposure wavefronts enable the formation of the master hologram in the third photosensitive material layer through 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 several additional, particularly superimposed, exposure wavefronts can also be advantageously used to interfere with the first exposure wavefront.

[0020] The master hologram formed in the third photosensitive material layer can be further processed following the exposure process, for example, fixed and replicated. The master hologram can be reproduced with a playback wave that essentially corresponds to the reconstruction wave, implementing the optical functions of the main and auxiliary holograms combined in the master hologram.

[0021] The method according to the proposed embodiment can be regarded as a multi-stage recording process with temporally successive steps, wherein the generation of the main hologram and the auxiliary hologram can be carried out independently of one another either in parallel or sequentially using different exposure devices.

[0022] 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 imprinted into the master hologram that deviates from the recording angle of the main hologram, in particular one that cannot usually be written together with the main hologram using a single recording process. Accordingly, the described embodiment enables an expansion of the optical functions of the master hologram with a high degree of design freedom.The recording angle can be an angle between the respective photosensitive material layer and the optical axis of the recording wave, which, for simplicity, is referenced to a surface normal of the photosensitive material layer. 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 intended deflection of the reconstruction wave onto the main hologram and the second exposure wavefront can be generated on the main hologram.Accordingly, the resulting master hologram can also be reproduced by irradiating light at the same angle as the reconstruction wave. Flat, i.e., large, exposure angles relative to the surface normal of the recording material can be particularly advantageous for projection applications with strong lateral light irradiation, as may be desirable, for example, in data glasses or head-up displays. Furthermore, a high angular bandwidth of the resulting master hologram can be advantageous for optical diagnostic applications, where it can contribute to increasing detection accuracy.

[0023] According to a further development of the previously described embodiment, 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 design options, the recording angle can be greater than 60° or even greater than 70°. The dimensions refer to a degree as an angular unit. By separately providing the auxiliary hologram with a recording angle that can be selected independently of the recording angle of the main hologram, correspondingly very flat deflection angles can be realized, which subsequently allow a flat playback angle of the resulting master hologram.

[0024] 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 according to the first recording configuration differs from a curvature of the recording wavefront according to the second recording configuration. This further increases the design freedom and the achievable complexity of the optical functions of the main and auxiliary holograms, as well as the resulting master hologram. In particular, the predefined curvature can be subject to complex conditions, for example, having different components with regard to sphere, asphere, or coma. Furthermore, an individual synthesis of the recording wavefront is conceivable, for example using Zernike polynomial functions.

[0025] According to one embodiment, the transmissive auxiliary hologram can be generated using an analog recording process. In an analog recording process, a hologram is recorded in a single exposure step with an expanded wavefront. Associated recording devices can, for example, comprise conventional optical elements that can be used for beam shaping and / or beam deflection. With an analog recording process, certain optical functions can be enabled or realized more cost-effectively 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 (explained below) and an analog-recorded auxiliary hologram are combined, the advantages of both recording methods can be efficiently combined and unified in the resulting master hologram.The high functional diversity of the digitally recorded main hologram can be usefully and specifically supplemented with the analogue auxiliary hologram. The main hologram and the auxiliary hologram, as well as the recording processes and recording devices used to record the main hologram and the auxiliary hologram, can be optimized with regard to their respective recording conditions and recording configurations without requiring a compromise solution to achieve the desired combination of optical functions with a common recording process. In principle, it is not excluded to produce the auxiliary hologram using a digital recording process, in particular a wavefront printing process.For example, if a digitally recorded main hologram and a digitally recorded auxiliary hologram are combined to generate the resulting master hologram, a particularly high degree of 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 regard to reconstruction by the auxiliary hologram. In other words, the optical properties of the reconstruction wave are selected such that it ideally reconstructs the auxiliary hologram.For example, an exposure angle of the reconstruction wave can correspond as closely as possible to the recording angle of the second recording configuration during generation of the auxiliary hologram, and / or a curvature of the first exposure wavefront formed with the reconstruction wave can correspond as closely as possible to a curvature of the recording wavefront according to the second recording configuration. A reconstruction wave matched to the auxiliary hologram can achieve optimized diffraction corresponding to the transmissive Bragg grating of the auxiliary hologram, which promotes optimized formation of a second exposure wavefront during the reflective diffraction of the reconstruction wave at the main hologram, thus optimizing the exposure process of the method as a whole.

[0026] According to one embodiment, the reconstruction wave can be generated such that, upon exposure of the layer stack, reconstruction of the transmissive auxiliary hologram and the reflective main hologram by means of the reconstruction wave occurs at least approximately under the Bragg condition. In other words, the optical properties of the reconstruction wave can be selected such that reconstruction of the main and auxiliary holograms is ensured under conditions close to the so-called Bragg configuration. For example, the wave reconstructed by the auxiliary hologram using the reconstruction wave can be matched to the recording wave of the first recording configuration of the main hologram, for example with regard to wavelength, collimation, recording angle, and / or curvature of the recording wavefront.This allows the diffracted wavefront of the reconstructed auxiliary hologram to generate a wavefront matching the main hologram, so that the main hologram is reconstructed in reflection, creating a diffracted exposure wavefront that propagates toward the unexposed third photosensitive material layer. By at least approximately fulfilling the Bragg condition of the Bragg grating underlying the main hologram, the generation of the exposure wavefront through diffraction at the auxiliary and main holograms can be optimized, allowing a resulting master hologram of high quality to be produced.

[0027] According to one embodiment, a plurality of different transmissive auxiliary holograms and / or a plurality of different reflective main holograms can be generated, and, depending on predetermined criteria for the resulting master hologram, a combination of a transmissive auxiliary hologram and a reflective main hologram can be selected to form the layer stack with the first material layer comprising the selected reflective main hologram, the second material layer comprising the selected transmissive auxiliary hologram, and an unexposed third photosensitive material layer. This makes it possible to make a manufacturing process for master holograms more flexible and to simplify and accelerate the production of different holograms for holographic optical elements.By providing and selecting suitable main and auxiliary holograms, an increased achievable variety of realizable hologram functions can be achieved. The generated transmissive auxiliary holograms and / or the generated reflective main holograms can thus form a kind of modular system, by means of which the individually desired properties of the master hologram can be combined during the exposure process. For example, different transmissive auxiliary holograms can be provided that realize different deflection functions with different solid angles. For example, different reflective main holograms can be provided with different optical function combinations.When generating, selecting, and combining the selected main and auxiliary holograms, particular care must be taken to ensure that the diffraction properties of the auxiliary hologram are matched to the main hologram in such a way that the main hologram can be reconstructed by diffraction of the reconstruction wave at the transmissive auxiliary hologram, thereby forming a second exposure wavefront that 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, with a transmissive auxiliary hologram then being selected from the plurality of transmissive auxiliary holograms for the layer stack.It is 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 from the plurality of reflective main holograms.

[0028] According to one embodiment, the method may additionally comprise the following further steps:

[0029] - generating a second transmissive auxiliary hologram with a recording wave according to a third recording configuration in a fourth photosensitive material layer;

[0030] - forming a layer stack with the first material layer comprising the reflective main hologram, the fourth material layer comprising the second transmissive auxiliary hologram, and the third photosensitive material layer comprising the master hologram; and

[0031] - exposing 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 such that diffraction of the reconstruction wave at the transmissive auxiliary hologram results in reconstruction of the reflective main hologram and thereby a second exposure wavefront is formed which interferes with the first exposure wavefront in the third photosensitive material layer to extend the master hologram.

[0032] This allows the optical functional density of the master hologram to be further increased. In principle, it is conceivable to repeat the above-described steps any number of times with different transmissive auxiliary holograms in order to incrementally supplement or refine the optical functions contained in the master hologram. In other words, additional functions can be gradually incorporated 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 implement different deflection functions with different solid angles.In principle, it is not excluded to replace the reflective main hologram with another reflective main hologram as an alternative or in addition to replacing the transmissive auxiliary hologram and to carry out another exposure in order to extend the master hologram in an analogous manner according to the steps described.

[0033] According to one embodiment, the first and / or second recording configuration can have a recording angle adjustment depending on an intended wavelength difference between the recording wave and a playback wave of the master hologram and / or depending on a known shrinkage compensation. This can achieve additional optimization of the auxiliary hologram and / or the main hologram to improve the playback properties of the master hologram. For example, a targeted slight adjustment 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 specifically increased, in particular for a specific target value of the diffraction efficiency.Shrinkage compensation refers to a lead for a technically induced shrinkage of the photosensitive material layers depending on the selected recording material.

[0034] 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 additional photosensitive material layers, for example, a fourth photosensitive material layer for exposing another auxiliary or main hologram into the master hologram. Silver halide films or dichromate gelatin films enable the production of particularly high-resolution holograms with a low noise component, thus enabling a high quality and complexity of the resulting master hologram.

[0035] According to one embodiment, after exposing 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 with an incoherent light source. This allows the master hologram to be fixed in a simple manner and ensures a high quality of the master hologram. The incoherent light source can be, for example, a white light source, a UV light source, or a near-UV light source. Exposure to the incoherent light source bleaches the third photosensitive material layer with the resulting master hologram and transfers it to a stationary state. For example, in a photopolymer film, the bleaching process causes crosslinking of the polymer and thus fixation of the inscribed holographic structure.In addition, the transparency properties of the master hologram can be controlled with the bleaching process to minimize stray light. In a multi-step exposure process for expanding the master hologram by replacing an auxiliary or main hologram with subsequent re-exposure, as explained with reference to the embodiment described above, it can be provided, in particular, that the described exposure process with the incoherent light source for fixation takes place only after the creation of a final master hologram, thus no further subsequent exposure of another auxiliary or main hologram is required.

[0036] According to one embodiment, the reflective main hologram can be designed as a complex main hologram with a plurality of superimposed holographic functions and / or the transmissive auxiliary hologram can be designed as a complex auxiliary hologram with a plurality of superimposed holographic functions. This can further increase the complexity of the produced master hologram. For example, in the complex main hologram and / or in the complex auxiliary hologram, several holographic solid angle deflection functions can be superimposed on one another, realizing divergent deflection functions with different solid angles. Such complex holograms can be produced with high quality, for example, by simultaneous exposure with an appropriately designed exposure device or by sequential exposure with different recording configurations.According to one embodiment, the reflective main hologram, particularly when the reflective main hologram is formed as a complex main hologram with a plurality of superimposed holographic functions, can be generated using a wavefront printing process in which at least one recording wavefront of the recording wave is modulated by a modulation device. The modulation device can comprise, 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 representing an optical function can be impressed on the recording wave, for example by modulating a laser beam forming the recording wave.Wavefront printing processes are also referred to as digital recording processes because, in the production of holograms using wavefront printing processes, individual sub-holograms in a matrix structure are exposed one after the other using a sequential exposure process by a suitably configured recording device. The size of a sub-hologram can vary between 50 pm and 1 mm, according to a non-limiting embodiment. The sub-holograms can have individual optical functions or, together, contribute to a higher-level optical function through a respective functional component.The respective optical function of a sub-hologram can be determined by a corresponding individual modulation of the recording wavefront, so that during sequential exposure during the wavefront printing process, different optical functions can be realized from sub-hologram to sub-hologram through a time-varying modulation of the recording wavefront. This allows a main hologram to be created with a high degree of optical complexity, functional diversity, and design freedom. In particular, by producing the main hologram using a wavefront printing process, a large portion of the desired optical functionalities of the holographic optical element to be manufactured can already be implemented, which can then be specifically supplemented during the production of the auxiliary hologram. In principle, however, it is not excluded to alternatively produce the main hologram using an analog recording process, which will be explained in more detail below.

[0037] By generating a reflective main hologram using a wavefront printing process, a complex master hologram with superimposed optical functions can be created without the need to expose an additional transmissive auxiliary hologram. Because the sub-holograms of the main hologram can be individually provided with optical functions using a wavefront printing process, which can also be produced with multiple superimposed optical functions, particularly during the wavefront printing process, a high functional density and optical complexity of the resulting master hologram can be achieved even with such a reflective main hologram.

[0038] According to a further development of the above-described embodiment, 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 aforementioned modulation devices. This enables a precise and versatile implementation of complex optical functions in the main hologram with a high degree of design freedom. In particular, an overlay of optical functions for each individual sub-hologram is enabled.

[0039] According to one embodiment, at least one sub-hologram with a collimating optical function can be generated in the reflective main hologram. This makes it possible to provide a master hologram for a holographic optical element, by which light incident into the holographic optical element can be collimated.

[0040] According to a further development, at least one sub-hologram with a converging main function and a collimating auxiliary function can be generated in the reflective main hologram. This allows multiple optical functions to be superimposed in the sub-hologram, and a complex master hologram can be formed using the reflective main hologram. In particular, multiple sub-holograms can be generated in the reflective main hologram, each 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 independently modulated recording wavefronts.

[0041] In the above-described embodiment, the main hologram can fulfill a so-called global point-to-point transformation as a global function, which can correspond to the converging main function. The global function of the reflective main hologram can correspond to a convergent wavefront generated by the 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, whereby a local individual beam deflected by the individual sub-hologram does not converge according to the global function, but is collimated according to the collimating auxiliary function.Accordingly, each subhologram can combine two optical functions, whereby a first optical function deflects the incident light beam according to the collimating auxiliary function, while a second optical function introduces a spherical contribution and forms a convergent wave from the divergent reconstruction wave according to the convergent main function.

[0042] Because the master hologram is created in a single photosensitive material layer, the master hologram can be easily reproduced in any number of pieces. In particular, according to one embodiment, the master hologram can be replicated in a continuous series production process. The holographic element created with the master hologram is therefore suitable for continuous reproduction in large quantities. For example, the master hologram can be continuously replicated using a roll-to-roll process. The invention also relates to a holographic optical element comprising 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 high optical complexity and quality. For example, by cleverly combining recording configurations of the reflective main hologram and the transmissive auxiliary hologram, a holographic optical element with a high optical functional diversity and special additional optical properties, such as a very flat playback angle or a combination of a converging optical function and a collimating optical function, can be created compared to conventional holographic optical elements. For example, an interference pattern resulting from a reconstruction of the main and auxiliary holograms can be inscribed in a single photosensitive material layer, whereby the optical functions of the main and auxiliary holograms can be distinguished in the master hologram using diffraction experiments or microscopic examination.The master hologram can, for example, be a projection hologram or a coupling hologram with extreme angles that can couple light into and out of a waveguide under total internal reflection. The holographic optical element can, for example, be integrated into a spectacle lens for use in data glasses. The holographic optical element can, in particular, comprise a master hologram produced according to the method described above.

[0043] According to one embodiment, the holographic optical element can be designed as an optical combiner. Accordingly, a plurality of optical functions can be implemented in the master hologram, thus providing a holographic optical element with a high functional density or diversity.

[0044] 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 using a wavefront printing process. Wavefront printing processes were explained in connection with the method described above. In particular, the main hologram can be a main hologram produced using a wavefront printing process in which at least one recording wavefront of the recording wave is modulated by a modulation device.

[0045] According to one embodiment, the reflective main hologram can have at least one sub-hologram with a collimating optical function. This can provide a master hologram for a holographic optical element, by which light incident into the holographic optical element can be collimated. In particular, the reflective main hologram can have several sub-holograms, each of which has a collimating optical function.

[0046] 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. This allows multiple optical functions to be superimposed in the sub-hologram, and a complex master hologram can be provided by means of the reflective main hologram. In particular, multiple sub-holograms can be formed in the reflective main hologram, each of which has a converging main function and a collimating auxiliary function.

[0047] According to one embodiment, the transmissive auxiliary hologram can be an analog auxiliary hologram. An analog auxiliary hologram is an auxiliary hologram produced using an analog recording process. Analog recording processes were 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 described recording methods and the resulting advantages of the main and auxiliary holograms for the resulting master hologram is possible. For example, with an analog auxiliary hologram, deflection functions with very flat deflection angles can be realized, which cannot be generated with a wavefront-printed main hologram.At the same time, the wavefront-printed main hologram can provide a hologram with a high optical functionality, which can be transferred to the master hologram by exposure.

[0048] The invention also relates to a transparent display system with a holographic optical element according to one of the aforementioned features. The transparent display system can be, for example, data glasses or a head-up display. The high complexity and quality of the master hologram integrated into the holographic optical element, as achieved here, allows for further technical optimization of such display systems. For example, complex master holograms with deflection functions can be used, which realize very flat deflection angles.

[0049] The invention also relates to a transparent display system comprising a holographic optical element and a transparent microlens array having a collimating optical function. Such a display system also makes it possible to implement a complex optical function in conjunction with a holographic optical element. The transparent microlens array can, for example, be a two-dimensional microlens array adapted 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 can, for example, have an analog-recorded main hologram.Analogous to the previously described sub-holograms of a wavefront-printed main hologram, individual microlenses of the transparent microlens array can be considered as optical subcomponents that can enable individual design and overlay of optical functions.

[0050] The invention also relates to an optical sensor system, in particular a laboratory diagnostic optical sensor system, comprising a holographic optical element according to one of the above-described features. The optical sensor system can be configured, for example, for examining biological samples. The optical sensor system can be used, for example, for fluorescence-based diagnostics. In such optical sensor systems, holograms are used, in particular, in the optical excitation and detection paths of the sensor system. If the optical sensor system comprises a holographic optical element according to one of the above-described features, the holographic optical element can provide a high functional diversity of spectral functions, in particular with a multitude of different deflection angles. This advantageously increases the detection accuracy and the detection bandwidth.

[0051] In general, in the context of this application, the words “a / an”, unless expressly defined otherwise, are not to be understood as a number, but as an indefinite article with the literal meaning of “at least one”.

[0052] The invention permits various embodiments and is explained in more detail below using an exemplary embodiment with the accompanying drawings. They show schematically:

[0053] Fig. 1 - a recording principle for generating a reflective

[0054] Main hologram according to an embodiment;

[0055] Fig. 2 - a recording principle for generating a transmissive

[0056] Auxiliary hologram according to an embodiment;

[0057] Fig. 3 - an exposure principle for producing a resulting

[0058] Master hologram using the main hologram and the auxiliary hologram in a layer stack according to an embodiment;

[0059] Fig. 4 - a master hologram replicated from the master hologram resulting from Fig. 3;

[0060] Fig. 5 - another embodiment of a master hologram formed from a main hologram; Fig. 6 - a transparent display system with a holographic optical element having a master hologram;

[0061] Fig. 7 - an optical sensor system with a holographic optical element having a master hologram;

[0062] Fig. 8 - a schematic process flow of a method for

[0063] Production of a master hologram for a holographic optical element according to an embodiment.

[0064] Fig. 1 shows a 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 with a recording wave 4a according to a first recording configuration. The recording wave 4a according 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, so that a recording angle Qi between the optical axis 11 and the surface normal 12 is present as a zero angle. The recording wave 4a can further be described by a recording wavefront 13 which has a predefined curvature KI according to the first recording configuration.According to the illustrated 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 4a is modulated by at least one modulation device (not shown in detail). The wavefront printing process can be used to form individual sub-holograms 15 with individual optical functions depending on the respective modulation of the recording wavefront 13, which together form a main hologram 1 with multiple optical functions or contribute proportionally to a higher-level optical function of the main hologram 1. The optical function of each sub-hologram 15 is locally inscribed 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 with the recording wave 4a in the first photosensitive material layer 5, thus forming a holographic grating. As schematically illustrated in Fig. 1, a plane wave can be selected for such an auxiliary wave 20, since this can be easily regenerated for later reconstruction of the reflective main hologram 1.

[0065] Fig. 2 shows a schematic diagram of a recording principle for generating a transmissive auxiliary hologram 2 according to an exemplary embodiment. For this purpose, a second photosensitive material layer 6 is provided and exposed with a recording wave 4b according to a second recording configuration. The recording wave 4b according to 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 θ2 that deviates from the recording angle Qi shown in Fig. 1 according to the first recording configuration. In particular, it can be seen that the recording angle θ2 according to the second recording configuration is greater than the recording angle Qi according to the first recording configuration. According to the exemplary embodiment shown in Fig. 2, the recording angle θ2 is greater than 45°.The recording wave 4b can further be described by a recording wavefront 13 having a predefined curvature K2 according to the second recording configuration, wherein the curvature K2 according to the second recording configuration can deviate from the curvature K1 according to the first recording configuration. According to the illustrated embodiment, the transmissive auxiliary hologram 2 is generated using an analog recording process. Accordingly, the auxiliary hologram 2 is recorded in a single exposure step with an expanded recording wavefront 13. This makes it easy to realize a recording angle θ2 greater than 45° using available exposure devices. The optical function of the transmissive auxiliary hologram 2 is inscribed into the second photosensitive material layer 6 by means of the recording wavefront 13 in 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 with the recording wave 4b in the second photosensitive material layer 6, thus forming a holographic grating. As schematically illustrated in Fig. 2, a plane wave can be selected for such an auxiliary wave 20, since this can be easily regenerated for later reconstruction of the transmissive auxiliary hologram 2.

[0066] Fig. 3 shows the formation of a layer stack 8, wherein the first photosensitive material layer 5 comprising the reflective main hologram 1, the second photosensitive material layer 6 comprising the transmissive auxiliary hologram 2, and an unexposed third photosensitive material layer 7 are arranged one above the other in the layer stack 8. Subsequently, the layer stack 8 is exposed to a reconstruction wave 9. As can be seen from a comparison of the recording wave 4b according to the second recording configuration in Fig. 2 and the reconstruction wave 9 in Fig.3, the optical properties of the reconstruction wave 9 are matched to a reconstruction of the transmissive auxiliary hologram 2. For example, an exposure angle γ of the reconstruction wave 9 can essentially correspond to the recording angle θ2 of the second recording configuration, and a curvature K3 of the first exposure wavefront 10a can essentially correspond to a curvature K2 of the recording wavefront 13 according to the second recording configuration. The reconstruction wave 9 forms a first exposure wavefront 10a and 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 diffraction of the reconstruction wave 9 at the transmissive auxiliary hologram 2 results in a reconstruction of the reflective main hologram 1.This creates second exposure wavefronts 10b in reflection, which propagate toward the third photosensitive material layer 7 and interfere with the first exposure wavefront 10a there. Thus, a resulting master hologram 3 with the optical functions of the main hologram 1 and the auxiliary hologram 2 is inscribed into the third photosensitive material layer 7. The resulting master hologram 3 can then be fixed, for example, by an exposure process with an incoherent light source and replicated as the final master hologram 3.

[0067] Fig. 4 shows such a final replicated master hologram 3, which is subjected to a playback wave 14. As can be seen from Fig. 4, thanks to the optical function of the auxiliary hologram 2, which is inscribed in addition to the holographic function of the main hologram, a large deflection angle ß for deflecting the incident light beam can be realized with the master hologram 3, whereby at the same time the functional diversity of the main hologram 1 can be implemented with the master hologram 3.

[0068] Fig. 5 shows a simplified schematic diagram of another embodiment of a master hologram 3 formed from a reflective main hologram 1. The main hologram 1 has, as schematically indicated, several sub-holograms 15 with a converging main function 21 and a collimating auxiliary function 22. The main hologram 1 can fulfill a so-called global point-to-point transformation as a global function, which can correspond to the converging main function 21. 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, whereby a local individual beam deflected by the individual sub-hologram 15 does not converge according to the global function, but is collimated according to the collimating auxiliary function 22. Accordingly, each sub-hologram 15 can combine two optical functions, whereby 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 from the divergent reconstruction wave 9 according to the convergent main function 21. By designing the Bragg structures on the sub-holograms 15 in this way, for example, any region 23 independent of a global hologram function of the main hologram 1 can be illuminated.

[0069] Fig. 6 shows a schematic diagram of a transparent display system 18 with a holographic optical element 16, which has a master hologram 3 according to one of the previously described features, for example, according to Fig. 4. The transparent display system 18 can be, for example, a head-up display or data glasses. Fig. 7 shows a schematic diagram of an optical sensor system 19 with a holographic optical element 16, which has a master hologram 3 according to one of the previously described features, for example, according to Fig. 4. The optical sensor system 19 can be, for example, a fluorescence-based diagnostic system.

[0070] Fig. 8 uses a schematic flow diagram to show method steps of a method 100 for producing a master hologram 3 for a holographic optical element 16 according to an exemplary embodiment. Accordingly, in a first step 110, a reflective main hologram 1 with a recording wave 4a according to a first recording configuration can be generated in a first photosensitive material layer 5, as shown in Fig. 1 using an exemplary embodiment. In a second step 120, a transmissive auxiliary hologram 2 with a recording wave 4b according to a second recording configuration can be generated in a second photosensitive material layer 6, as shown in Fig. 2 using an exemplary embodiment.In a third step 130, a layer stack 8 can be formed 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.Subsequently, the layer stack 8 can be exposed to a reconstruction wave 9, wherein the reconstruction wave 9 forms a first exposure wavefront 10a that 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 such that diffraction of the reconstruction wave 9 at the transmissive auxiliary hologram 2 reconstructs the reflective main hologram 1, thereby forming a second exposure wavefront 10b that interferes with the first exposure wavefront 10a in the third photosensitive material layer 7 to form a resulting master hologram 3. These steps 130 and 140 have been explained additionally by way of example with reference to Fig. 3.

[0071] Using 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 various hologram recording configurations can be combined in a master hologram 3. In this case, a master hologram 3 with a high degree of complexity and quality can be produced. The method 100 according to the illustrated embodiment is associated with a high degree of design freedom and adaptability, in particular due to the individual design option for the main hologram 1 and the auxiliary hologram 2. Furthermore, by combining the holographic functions in a photosensitive material layer 7, a master hologram 3 that can be replicated in large quantities can be efficiently produced.

Claims

Claims 1. 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, which is further developed into a complex master hologram (3) having 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).

2. The 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) having the reflective main hologram (1), which has the transmissive auxiliary hologram (2) having a second material layer (6) 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 diffraction of the reconstruction wave (9) at the transmissive auxiliary hologram (2) results in a reconstruction of the reflective main hologram (1), and as a result, a second exposure wavefront (10b) is formed, which interferes (140) with the first exposure wavefront (10a) in the third photosensitive material layer (7) to form a resulting master hologram (3).

3. Method (100) according to claim 2, wherein the generation of the reflective main hologram (1) and the transmissive auxiliary hologram (2) each takes place at a predefined recording angle (a1, a2) between an optical axis (11) of the recording shaft (4a, 4b) and a surface normal (12) of the first or second photosensitive material layer (5, 6) and wherein the recording angle (a2) of the second recording configuration deviates from the recording angle (a1) of the first recording configuration, in particular is greater than the recording angle (a1) of the first recording configuration.

4. The method (100) according to claim 3, wherein the recording angle (a2) of the second recording configuration is an angle greater than 45° to the surface normal (12) of the second photosensitive material layer (6).

5. Method (100) according to one of claims 2 to 4, wherein the generation of the reflective main hologram (1) and the transmissive auxiliary hologram (2) is each carried out with a predefined curvature (K1, K2) of a recording wavefront (13) of the recording wave (4a, 4b) and wherein the curvature (K1) of the recording wavefront (13) according to the first recording configuration deviates from a curvature (K2) of the recording wavefront (13) according to the second recording configuration.

6. Method (100) according to one of claims 2 to 5, wherein the transmissive auxiliary hologram (2) is generated by means of an analog recording process.

7. 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).

8. Method (100) according to one of claims 2 to 7, wherein the reconstruction wave (9) is generated such that upon exposure of the layer stack (8), a reconstruction of the transmissive auxiliary hologram (2) and the reflective main hologram (1) by means of the reconstruction wave (9) takes place at least approximately under the Bragg condition.

9. 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, depending on predetermined criteria for the resulting master hologram (3), a combination of a transmissive auxiliary hologram (2) and a reflective main hologram (1) is selected in order to form the layer stack (8) with the first material layer (5) comprising the selected reflective main hologram (1), the second material layer (6) comprising the selected transmissive auxiliary hologram (2) and an unexposed third photosensitive material layer (7).

10. The method (100) according to any one of claims 2 to 9, additionally comprising 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) comprising the reflective main hologram (1), the fourth material layer comprising the second transmissive auxiliary hologram (2), and the third photosensitive material layer (7) comprising the master hologram (3); and - exposing the layer stack (8) to 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 diffraction of the reconstruction wave (9) at the transmissive auxiliary hologram (2) results in a reconstruction of the reflective main hologram (1), and as a result, a second exposure wavefront (10b) is formed which interferes with the first exposure wavefront (10a) in the third photosensitive material layer (7) to extend the master hologram (3).

11. Method (100) according to one of claims 2 to 10, wherein the first and / or the second recording configuration comprises a recording angle adjustment depending on an intended wavelength difference between the recording wave (4a, 4b) and a playback wave (14) of the master hologram (3) and / or depending on a known shrinkage compensation.

12. 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.

13. Method (100) according to one of claims 2 to 12, wherein after exposing the layer stack (8) with the reconstruction wave (9) to form the resulting or extended master hologram (3), the master hologram (3) is fixed by an exposure process with an incoherent light source.

14. 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.

15. 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.

16. The 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.

17. Method (100) according to one of claims 15 or 16, wherein at least one sub-hologram (15) with a collimating optical function is generated in the reflective main hologram (1).

18. The method according to claim 17, wherein in the reflective main hologram (1) at least one sub-hologram (15) with a converging main function (21) and a collimating auxiliary function (22) is generated.

19. Method (100) according to one of the preceding claims, wherein the master hologram (3) is replicated in a continuous series production process.

20. Holographic optical element (16), comprising a master hologram (3) formed by superimposed reconstruction of a reflective main hologram (1) and 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).

21. Holographic optical element (16) according to claim 20, wherein the holographic optical element (16) is designed as an optical combiner.

22. Holographic optical element (16) according to claim 20 or 21, wherein the reflective main hologram (1) is a wavefront printed main hologram (1).

23. Holographic optical element (16) according to claim 22, wherein the reflective main hologram (1) has at least one sub-hologram (15) with a collimating optical function.

24. Holographic optical element (16) according to claim 23, wherein the reflective main hologram (1) has at least one sub-hologram (15) with a converging main function (21) and a collimating auxiliary function (22).

25. Holographic optical element (16) according to one of claims 20 to 24, wherein the transmissive auxiliary hologram (2) is an analog auxiliary hologram (2).

26. Holographic optical element (16) according to one of claims 20 to 25, wherein the master hologram (3) is created by means of a method (100) according to one of Claims 1 to 19.

27. Transparent display system (18) with a holographic optical element (16) according to one of claims 20 to 26.

28. Transparent display system (18) with a holographic optical element (16) according to one of claims 20 to 26 and a transparent microlens array having a collimating optical function.

29. Optical sensor system (19), in particular laboratory diagnostic optical sensor system (19), with a holographic optical element (16) according to one of claims 20 to 26.

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