Holographic wavefront manipulator, and optical assembly

Abstract

The invention relates to a wavefront manipulator (10) which comprises a first holographic optical element (11), having a front side (13) and a rear side (15), and a second holographic optical element (12), having a front side (14) and a rear side (16), which holographic optical elements are arranged one after the other in a beam path (3), wherein the second holographic optical element (12) is arranged downstream of the first holographic optical element (11) in the beam path (3), wherein the front side (13) of the first holographic optical element (11) is arranged facing the rear side (16) of the second holographic optical element (12). The rear side (15) of the first holographic optical element (11) comprises a surface designed for total reflection of light which is incident on the surface from the front side (13) of the first holographic optical element (11). The first holographic optical element (11) comprises at least one hologram which is designed to diffract light, which is radiated through the rear side (15) into the first holographic optical element (11), towards the rear side (15) such that the diffracted light is totally reflected from the rear side (15) towards the front side (13). The front side (14) of the second holographic optical element (12) comprises a surface designed for total reflection of light which is incident on the surface from the rear side (15) of the first holographic optical element (11). The second holographic optical element (12) comprises at least one hologram which is designed to diffract light, which is reflected from the surface of the front side (14) of the second holographic optical element (12) into the second holographic optical element (12), towards the front side (14) such that the diffracted light exits through the front side (14) of the second holographic optical element (12).

Description

[0001] Holographic wavefront manipulator and optical arrangement

[0002] The present invention relates to a holographic wavefront manipulator and an optical arrangement, for example a display device.

[0003] In a variety of optical applications, wavefront manipulators comprising holographic optical elements are used for beam guidance and shaping. Arrangements in which holographic optical elements or holograms are stacked and holograms from different optical elements are aligned for reflection have proven advantageous. The state of the art in this regard is described, for example, in DE 10 2021 105 830 A1.

[0004] The arrangement of several holograms, which are aligned for reflection, as a stack is also referred to here as Z-configurations. In particular, two volume hologram gratings can be used for reflection within the stack as part of an optical arrangement designed for transmission. In other words, the entire optical system or arrangement operates in transmission mode, and reflection only occurs within the arrangement or system consisting of a stack of holograms.

[0005] For example, light from an imaging unit or light source can first be transmitted through a first hologram, which is not efficient for the angle and wavelength spectrum of the incident light. After transmission through the first hologram, the light is diffracted or reflected back towards the first hologram by a second hologram. Typically, the first diffraction and reflection at the second hologram changes the full width at half maximum (FWHM) of the angular spectrum. This allows the light to be collimated, for example. During the first diffraction and reflection, the light is reflected or emitted at a different angle and then diffracted or reflected again by the first hologram. After the second diffraction and reflection, the light is transmitted through the second hologram.The second diffraction or reflection at the first hologram grating generates the desired wavefront or wavefront function, for example, for a virtual image. As a result, the entire system operates in transmission mode.

[0006] The described Z-configuration generally has the advantage that it can be operated in transmission mode while simultaneously offering a robust and compact design with which wavefronts can be precisely manipulated in large angular and wavelength ranges.

[0007] The Z-configuration can also be used in conjunction with diffusers. Unlike a reflection setup, this allows images to be projected in a direction outside the system encompassing the image source or light source. This makes it possible, for example, to use vehicle windows to project information visible from both the outside and / or inside. Another application is holographic projection screens for offices, conference rooms, information booths, etc., where the same information can be projected simultaneously onto both sides of a screen and perceived from defined areas or eyeboxes, while the projection screen itself remains transparent.Light that is not completely diffracted within a Z-configuration and therefore remains in the system can be directed to a beam trap, located, for example, on the side or edge of the Z-configuration, and absorbed there to avoid unwanted stray light or imaging errors. The direction of the undiffracted light can be achieved via total internal reflection (TIR).

[0008] In the context described, the aim is to reduce filtering effects between the different holograms and to generate a homogeneous wavefront. Furthermore, backscattering into the imaging unit and scattered light in general should be reduced or avoided.

[0009] Against this background, it is an object of the present invention to provide an advantageous wavefront manipulator which, in particular, at least partially satisfies the aforementioned requirements. A further object is to provide an advantageous optical arrangement, e.g., in the form of a head-up display, a projection screen, or a display panel.

[0010] These problems are solved by a wavefront manipulator according to claim 1 and an optical arrangement according to claims 14 and 16. The dependent claims contain further advantageous embodiments of the invention.

[0011] The wavefront manipulator according to the invention comprises a first holographic optical element and a second holographic optical element. The first holographic optical element has a front and a back. The second holographic optical element also has a front and a back. The first and second holographic optical elements are arranged sequentially or one after the other in a beam path. The second holographic optical element is arranged downstream of the first holographic optical element in the beam path. In other words, the second holographic optical element is arranged downstream of the first holographic optical element. The front of the first holographic optical element faces the back of the second holographic optical element.

[0012] The back side of the first holographic optical element comprises a surface designed for total internal reflection of light incident on the surface from the front side of the first holographic optical element. The first holographic optical element comprises at least one hologram, e.g., a volume hologram, designed to diffract or reflect light incident on the back side of the first holographic optical element in such a way that the diffracted light is totally reflected at the back side, i.e., at the surface designed for total internal reflection, of the first holographic optical element towards the front side of the first holographic optical element.The hologram is preferably designed to diffract or reflect light towards the rear in such a way that the diffracted light strikes the rear at an angle greater than the critical angle of total internal reflection.

[0013] The front face of the second holographic optical element comprises a surface designed for total internal reflection of light incident on the surface from the back face of the first holographic optical element. The second holographic optical element comprises at least one hologram, e.g., a volume hologram, designed to diffract or reflect light reflected from the surface (i.e., the totally reflective surface) of the front face of the second holographic optical element towards the front face, such that the diffracted light exits through the front face of the second holographic optical element.

[0014] The wavefront manipulator according to the invention can in particular be arranged in the beam path of a projection or display device, e.g. a head-up display, between an imaging unit (PGU - Picture Generating Unit) or a projection lens and a

[0015] It must be designed for projection.

[0016] The wavefront manipulator according to the invention has the advantage that the described beam guidance reduces, e.g., halves, the light transmission through a transition, gap, or interface between the holographic optical elements. The beam path is also shortened. This significantly reduces filter effects, scattered light, and aberrations, such as absorption, as well as backscattering towards a light source or image sensor.

[0017] The holograms of the at least two holographic elements are preferably designed to be reflective for at least one defined wavelength and a defined angle of incidence. Light waves of the at least one defined wavelength and the defined angle of incidence are thus efficiently diffracted. Preferably, the holographic elements are also designed to be transmissive, in other words, transmissive for wavelengths that do not correspond to the at least one defined wavelength and have an angle of incidence outside the defined angle of incidence.

[0018] The use of reflection holograms has the advantage that their intrinsic properties can be utilized. These holograms exhibit fundamentally different efficiency curves than transmission holograms, with the efficiency curves of reflection holograms offering wavelength selectivity, which, among other things, prevents the formation of double images. Furthermore, the transmissive design and the use of reflection holograms reduce filter effects between the holograms.

[0019] Advantageously, at least one, and preferably two, of the holograms is efficiently designed for a plurality of angles of incidence and / or for a plurality of non-overlapping angle ranges of incidence. The at least two holograms are preferably designed such that a hologram of the first holographic optical element is associated with a hologram of the second holographic optical element, and in particular, the holograms are aligned for reflection. In other words, the at least two holographic optical elements are designed such that light emitted from the front face of a first holographic element, of at least one wavelength and at least one angle of incidence, is reflected by the hologram of the second holographic optical element.

[0020] Preferably, mutually associated holograms are designed to be pointwise diffraction-efficient with respect to each other. To determine the diffraction efficiency, either the intensity of the first diffraction order is set in relation to the sum of the intensity of the first diffraction order and the intensity of the zeroth diffraction order, or the intensity of the first diffraction order is set in relation to the total incident light intensity. In other words, pointwise diffraction efficiency means that at least one point of a first hologram is designed to diffract light of at least a defined wavelength and a defined angle of incidence to a point of a second hologram, which in turn diffractes the light diffracted by the first hologram.For example, the first hologram can be designed to diffract waves of a specific wavelength and angle of incidence to the second hologram with an efficiency of over 90 percent, and the second hologram can be designed to diffract the waves diffracted by the first hologram into the final, desired direction with an efficiency of over 90 percent. This facilitates the projection of a multi-colored image, especially an aberration-corrected multi-colored image.

[0021] In an advantageous embodiment, the front surface of the first holographic optical element is designed to emit totally internally reflected light from its rear surface towards the rear surface, or in other words, the rear surface of the second holographic optical element. For this purpose, the front surface of the first holographic optical element can be configured to transmit light with angles of incidence and wavelengths of the totally internally reflected light from its rear surface.

[0022] In another variant, the wavefront manipulator can include a beam trap for absorbing light. This has the advantage of reducing the propagation of scattered light and thus minimizing or avoiding unwanted artifacts potentially caused by scattered light.

[0023] The beam trap can be configured to absorb light that is not diffracted by the at least one hologram of the second and / or first holographic optical element and / or light that is reflected between the back of the first holographic optical element and the front of the second holographic optical element, and in particular light that is not emitted via the front of the second holographic optical element.

[0024] The first holographic optical element can have at least one side surface that connects the front and back surfaces of the first holographic optical element and / or adjoins the front and back surfaces. The second holographic optical element can have at least one side surface that connects the front and back surfaces of the second holographic optical element and / or adjoins the front and back surfaces. Advantageously, the beam trap is arranged on at least one side surface of the first and / or second holographic optical element. This design enables a discreet and efficient dissipation of potential stray light from the wavefront manipulator, i.e., without disturbing or impairing the beam path. The wavefront manipulator can be designed as a diffuser, in particular as a holographic diffuser.This offers diverse application options in the context of display devices.

[0025] The front of the first holographic optical element and the back of the second holographic optical element can be directly adjacent to each other, or in other words, directly one behind the other in the beam path, e.g., laminated together. In this configuration, there is therefore no gap between the front of the first holographic optical element and the back of the second holographic optical element.

[0026] Alternatively, a substrate can be arranged between the front of the first holographic optical element and the back of the second holographic optical element. The substrate can have a refractive index similar to that of the holographic optical elements, i.e., a refractive index that differs from that of the first holographic optical element and / or the second holographic optical element by a maximum of 0.2, preferably a maximum of 0.1, e.g., by between 0.01 and 0.04.

[0027] In another variant, at least one additional optical element, e.g., an optically active or wavefront-manipulating optical element, is arranged between the front of the first holographic optical element and the back of the second holographic optical element. The additional optical element can comprise at least one polarization filter and / or at least one delay plate (A / 2 plate).

[0028] At least one coating and / or another optical element can be arranged on the back side of the first holographic optical element and / or on the front side of the second holographic optical element. The coating preferably has a lower refractive index than a substrate of the first and / or second holographic optical element and / or than the surface of the front and / or back side of the first and / or second holographic optical element. The coating can comprise optical cement and / or optical adhesive, e.g., optically clear adhesive (OCA), and / or a gas, e.g., air or nitrogen. The other optical element can be configured as a transparent cover element, which may comprise, for example, glass or plastic.

[0029] The optical arrangement according to a first embodiment of the invention, which can be configured, for example, as an image display device, comprises an image transmitter, i.e., a PGU, a projector, or a display for emitting the image content to be projected. The optical arrangement includes a wavefront manipulator according to the invention, as previously described, which is arranged in the beam path downstream of the image transmitter. The optical arrangement can be configured as a head-up display and / or as an at least partially transparent display device or screen. The optical arrangement according to the invention has the features and advantages already described in connection with the wavefront manipulator according to the invention.

[0030] The optical arrangement according to a second embodiment of the invention, which can be configured, for example, as an image acquisition device, comprises an image sensor. The optical arrangement includes a previously described wavefront manipulator according to the invention, which is arranged in the beam path upstream of the image sensor. The optical arrangement can be configured as a camera, for example, in the form of a HoloCam. The optical arrangement according to the invention has the features and advantages already described in connection with the wavefront manipulator according to the invention.

[0031] The invention is explained in more detail below with reference to exemplary embodiments and the accompanying figures. Although the invention is illustrated and described in detail by the preferred embodiments, the invention is not limited by the disclosed examples and other variations can be derived from them by a person skilled in the art without departing from the scope of protection of the invention.

[0032] The figures are not necessarily detailed or to scale and may be enlarged or reduced to provide a better overview. Therefore, the functional details disclosed here are not to be understood as limiting, but merely as an illustrative basis to guide those skilled in this field of technology in using the present invention in a variety of ways.

[0033] The expression "and / or" used here, when used in a series of two or more elements, means that each of the listed elements can be used alone, or any combination of two or more of the listed elements can be used. For example, when describing a composition containing the components A, B, and / or C, the composition can contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination.

[0034] Fig. 1 schematically shows a first variant of a wavefront manipulator as part of an optical arrangement according to the prior art.

[0035] Fig. 2 schematically shows a second variant of a wavefront manipulator as part of an optical arrangement according to the prior art.

[0036] Fig. 3 schematically shows a third variant of a wavefront manipulator as part of an optical arrangement according to the prior art.

[0037] Fig. 4 schematically shows a first embodiment of a wavefront manipulator and an optical arrangement according to the invention. Fig. 5 schematically shows a second embodiment of a wavefront manipulator and an optical arrangement according to the invention.

[0038] Fig. 6 schematically shows a third variant of a wavefront manipulator and an optical arrangement according to the invention.

[0039] Fig. 7 schematically shows a fourth variant of a wavefront manipulator and an optical arrangement according to the invention.

[0040] The following describes wavefront manipulators 1 with a Z-configuration according to the prior art, based on Figures 1 to 3. The wavefront manipulators 1 shown each comprise a first holographic optical element 11 and a second holographic optical element 12. In the beam path 3, starting from a light source or a PGU or image generator 2, the second holographic optical element 12 is arranged downstream of the first holographic optical element 11.

[0041] The first holographic optical element 11 has a front face 13 and a back face 15. The second holographic optical element 12 has a front face 14 and a back face 16. The first holographic optical element 11 and the second holographic optical element 12 are stacked, i.e., arranged one on top of the other, with the front face 13 of the first holographic optical element 11 facing or adjacent to the back face 16 of the second holographic optical element 12. The distance between the first holographic optical element 11 and the second optical element 12 is shown enlarged in the figures to illustrate the beam path 3. Typically, the distance is zero or nearly zero, or at least as small as possible. Depending on the specific application, the distance can also be in the range of 1 inch or 25.4 mm.

[0042] The light emitted by the image generator 2 first passes through the first holographic optical element 11. The at least one hologram of the first holographic optical element 11 is not efficient with respect to the angular and wavelength spectrum of the incident light. In other words, the incident light is not diffracted by the hologram. The light is then diffracted or reflected by at least one hologram of the second holographic optical element 12 and emitted towards the front face 13 of the first holographic optical element 11. During diffraction by the hologram of the second holographic optical element 12, the full width at half maximum (FWHM) of the angular spectrum of the light is typically changed, for example, the light is collimated.

[0043] The light incident on the front face 13 of the first holographic optical element 11 is diffracted or reflected by at least one hologram of the first holographic optical element 11 and emitted towards the rear face 16 of the second holographic optical element. This process generates or emits the resulting wavefront. The light reflected by the hologram of the first holographic optical element 11 transmits to the second holographic optical element 12, i.e., it radiates through the rear face 16 and the front face 14 of the second holographic optical element 12. The at least one hologram of the second holographic optical element 12 is not efficient with respect to the angular and wavelength spectrum of the light reflected by the hologram of the first holographic optical element 11.In other words, the incident light is not diffracted by the hologram of the second holographic optical element 12. A rearward extension of the light rays 3 emitted by the wavefront manipulator 1 shown in Figure 1 results in a virtual pixel 4. Potentially generated scattered light is indicated by dashed arrows. Figure 2 shows an application of a wavefront manipulator 1 with a Z-configuration as a diffuser. Here, the hologram of the first holographic optical element 11 acts as a diffuser. The diffuse light emitted in this way is labeled with the reference numeral 5. Such a configuration makes it possible to project image content or information relating to an optical system outwards, while all important system components, such as the image generator 2 in particular, can be arranged inside the system, i.e., protected from environmental influences.This represents an advantage of a wavefront manipulator 1 operated in transmission mode, as in the variants shown, compared to a wavefront manipulator operated in reflection mode. However, due to the relatively large angular spectrum of the light scattered by the diffuser or the first holographic optical element 11, the second holographic optical element 12 has a strong filtering effect.

[0044] In the variant shown in Figure 3, a key difference from the variants in Figures 1 and 2 is that the light is diffracted by the second holographic optical element 12 at an angle greater than the critical angle for total internal reflection. This means that the light is coupled into the substrate that carries the holographic optical elements. Another difference from the variants in Figures 1 and 2 is that the first holographic optical element 11 and the second holographic optical element 12 are in contact with each other, specifically optical contact. They can be laminated onto a common substrate or directly onto one another, thus forming a single component or unit, as indicated by the dashed lines.

[0045] In the variant shown in Figure 3, in contrast to the variants in Figures 1 and 2, a beam trap 6 is optionally provided, which absorbs light propagating between the front 13 of the first holographic optical element 11 and the back 16 of the second holographic optical element 12, in particular light propagating by total internal reflection between the two holographic optical elements 11 and 12. This reduces the propagation of unwanted scattered light. In the variant shown, the beam trap 6 is arranged on a side surface of the wavefront manipulator 1, located at the bottom of Figure 3. This side surface comprises a side surface 17 connecting the front 13 and the back 15 of the first holographic optical element 11 and a side surface 18 connecting the front 14 and the back 16 of the second holographic optical element 12.

[0046] Figure 4 schematically shows a first embodiment of a wavefront manipulator 10 according to the invention as part of an optical arrangement 20 according to the invention, which includes an image sensor 2. In contrast to the wavefront manipulators described above according to the prior art, the beam path 3 through the wavefront manipulator 10 according to the invention can be described as follows. Light coming from the image sensor 2 is first transmitted through the surface of the back side 15 of the first holographic optical element 11. The light is then diffracted by at least one hologram, e.g., a volume hologram, of the first holographic optical element 11 and reflected towards the surface of the back side 15 of the first holographic optical element.The light strikes the surface of the back side 15 of the first holographic optical element at an angle greater than the critical angle for total internal reflection and is totally reflected there.

[0047] The totally reflected light is then emitted through the front surface 13 of the first holographic optical element 11 towards the second holographic optical element 12 and enters it through the back surface 16. The hologram of the first holographic optical element 11 is not efficient for the totally reflected light at the surface of the back surface 15. In other words, the light is not manipulated by the hologram. In the variant shown in Figure 4, no manipulation of the beam path occurs during the transition of the light from the first holographic optical element 11 to the second holographic optical element 12.

[0048] The light incident from the first holographic optical element 11 into the second holographic optical element 12, for which the at least one hologram, e.g., volume hologram, of the second holographic optical element 12 is not efficient, is totally internally reflected at the surface of the front face 14 of the second holographic optical element 12. The totally internally reflected light from the surface of the front face 14 of the second holographic optical element 12 is then diffracted by the at least one hologram of the second holographic optical element 12 and reflected towards the front face 14. This generates the wavefront to be emitted by the front face 14.Light that is not diffracted by the hologram of the second holographic optical element 12 and is emitted in the direction of the first holographic optical element 11 can be absorbed by the beam trap 6 after one or more total internal reflections.

[0049] In another variant, the space between the first holographic optical element 11 and the second holographic optical element 12 can be filled with a substrate. The substrate can have the same or a similar refractive index as the materials of the first holographic optical element 11 and / or the second holographic optical element 12. In other words, another component, liquid, or gas can be arranged between the front face 13 of the first holographic optical element 11 and the back face 16 of the second holographic optical element 12. This configuration allows, for example, the optimization of the transmission of non-diffractified light to the beam trap 6 by total internal reflection in the substrate. The first holographic optical element 11 and the second holographic optical element 12 can also be arranged directly on top of or adjacent to each other, e.g.,laminated together.

[0050] As in the variant shown in Figure 3, the light can be diffracted by the second holographic optical element 12 at an angle greater than the critical angle for total internal reflection. This means that the light is coupled into the substrate that carries the holographic optical elements 11 and 12. The first holographic optical element 11 and the second holographic optical element 12 are preferably in contact with each other, particularly optical contact. They can be laminated onto a common substrate or directly onto one another, thus forming a single component or unit. As already mentioned, a substrate with a refractive index similar to that of the holographic optical elements 11 and 12 can also be arranged directly, i.e., without a gap, between the first 11 and the second 12 holographic optical elements.

[0051] In comparison to wavefront manipulators according to the prior art, the wavefront manipulator according to the invention reduces the length of the beam path and the number of light passes through a gap or interface between the first holographic optical element 11 and the second holographic optical element 12. This reduces or eliminates potential aberrations, such as absorption. Furthermore, the filtering effect of the second holographic optical element 12 is reduced.

[0052] The variant shown in Figure 5 builds upon the diffuser configuration shown in Figure 2, with the at least one hologram of the second holographic optical element 12 acting as a diffuser in the variant shown in Figure 5. Here, too, the filtering effect of the second holographic optical element 12 is reduced compared to the configuration shown in Figure 2. In the variant shown in Figure 6, starting from the variant shown in Figure 4, a further optical element 7 is arranged between the front 13 of the first holographic optical element 11 and the back 16 of the second holographic optical element. This further optical element 7 can, for example, be a polarizing filter, a retardation plate, or one or more coatings. Filtering effects can be reduced or avoided, for example, by means of this further optical element 7.Furthermore, stronger angular separation or spectral separation can be performed for the different efficiency curves of the individual holograms. For example, in the case of a broadband light source, individual frequency ranges can be filtered out, especially those for which the respective hologram is not efficient. The holograms of the different holographic optical elements 11 and 12 can be better separated in their effect by means of the additional optical element 7, thereby avoiding unwanted stray light or aberrations.

[0053] In the variant shown in Figure 7, starting from the variant shown in Figure 4, additional optical elements are applied to the back 15 of the first holographic optical element 11 and to the front 14 of the second holographic optical element 12. These are, in each case, a cover glass or a plastic cover 9, which is applied to the surface of the back 15 and the surface of the front 14 by means of an optical cement 8 to protect the respective surface. This variant has the advantage that the aforementioned surfaces, which are designed for total internal reflection, are protected against contamination, which in turn can lead to faulty images and / or artifacts.

[0054] Preferably, an optical cement or adhesive 8 in the form of a transparent optical adhesive with a low refractive index can be used. This optimizes total internal reflection at the respective surfaces of the front 14 and the back 15 and prevents the generation and propagation of scattered light. In an exemplary embodiment, the angle of incidence within the first holographic optical element 11 onto the back 15 and / or the angle of incidence within the second holographic optical element 12 onto the surface of the front 14 can be at least 70 degrees. The refractive index of the substrate of the first and / or second holographic optical element 11 or 12 can be 1.5, and the refractive index of the optical cement or adhesive 8 used can be less than 1.4 in this case.

[0055] As an alternative to the use of optical cement or adhesive 8, a space between the respective holographic optical element 11 or 12 and a cover glass or plastic cover 9 can be filled with air or nitrogen or another fluid.

[0056] Reference symbol list:

[0057] 1 Wavefront manipulator

[0058] 2 Imagers / PGU

[0059] 3 Beam path

[0060] 4 virtual pixels

[0061] 5 diffuse light

[0062] 6 beam trap

[0063] 7 optical element

[0064] 8 Cover glass / plastic cover

[0065] 9 optical cement or adhesive

[0066] 10 Wavefront Manipulator

[0067] 11 first holographic optical element

[0068] 12 second holographic optical element

[0069] 13 Front

[0070] 14 Front

[0071] 15 Back

[0072] 16 Back

[0073] 17 side surface

[0074] 18 side surface

[0075] 20 optical arrangement

Claims

Patent claims 1. Wavefront manipulator (10) comprising a first holographic optical element (11) with a front (13) and a back (15) and a second holographic optical element (12) with a front (14) and a back (16) arranged sequentially in a beam path (3), wherein the second holographic optical element (12) is arranged downstream of the first holographic optical element (11) in the beam path (3), wherein the front (13) of the first holographic optical element (11) faces the back (16) of the second holographic optical element (12), characterized in that the back (15) of the first holographic optical element (11) comprises a surface designed for total internal reflection of light incident on the surface from the front (13) of the first holographic optical element (11).the first holographic optical element (11) comprises at least one hologram configured to diffract light incident on the first holographic optical element (11) through the back (15) in the direction of the back (15) such that the diffracted light is totally reflected at the back (15) in the direction of the front (13); the front (14) of the second holographic optical element (12) comprises a surface configured for total reflection of light incident on the surface from the back (15) of the first holographic optical element (11); and the second holographic optical element (12) comprises at least one hologram configured to diffract light reflected from the surface of the front (14) of the second holographic optical element (12) into the second holographic optical element (12) in the direction of the front (14).that the diffracted light exits through the front (14) of the second holographic optical element (12).

2. Wavefront manipulator (10) according to claim 1, characterized in that the front (13) of the first holographic optical element (11) is designed to emit totally reflected light from the rear (15) of the first holographic optical element (11) towards the rear (16) of the second holographic optical element (12).

3. Wavefront manipulator (10) according to claim 1 or 2, characterized in that the wavefront manipulator (10) comprises a beam trap (6) for absorbing light.

4. Wavefront manipulator (10) according to claim 3, characterized in that the beam trap (6) is configured to absorb light which is not diffracted by the at least one hologram of the second holographic optical element (12) and / or light which is reflected between the back (15) of the first holographic optical element (11) and the front (14) of the second holographic optical element (12).

5. Wavefront manipulator (10) according to claim 3 or 4, characterized in that the first holographic optical element (11) has at least one side surface (17) having which connects the front (13) and the back (15) of the first holographic optical element (11) and / or the second holographic optical element (12) has at least one side surface (18) having which connects the front (14) and the back (16) of the second holographic optical element (12) and the beam trap (6) is arranged on at least one side surface (17, 18) of the first (11) and / or second holographic optical element (12).

6. Wavefront manipulator (10) according to one of claims 1 to 5, characterized in that the wavefront manipulator (10) is designed as a diffuser.

7. Wavefront manipulator (10) according to one of claims 1 to 6, characterized in that the front (13) of the first holographic optical element (11 ) and the back (16) of the second holographic optical element (12) are arranged directly adjacent to each other or a substrate is arranged between the front (13) of the first holographic optical element (11 ) and the back (16) of the second holographic optical element (12).

8. Wavefront manipulator (10) according to one of claims 1 to 7, characterized in that at least one additional optical element (7) is arranged between the front (13) of the first holographic optical element (11) and the back (16) of the second holographic optical element (12).

9. Wavefront manipulator (10) according to claim 8, characterized in that the additional optical element (7) comprises at least one polarization filter and / or at least one retardation plate.

10. Wavefront manipulator (10) according to one of claims 1 to 9, characterized in that at least one coating (8) and / or a further optical element (8, 9) is arranged on the back (15) of the first holographic optical element (11) and / or on the front (14) of the second holographic optical element (12).

11. Wavefront manipulator (10) according to claim 10, characterized in that the coating (8) has a lower refractive index than a substrate of the first (11) and / or second holographic optical element (12) and / or than the surface of the front (13, 14) and / or reverse side (15, 16) of the first and / or second holographic optical element (11, 12).

12. Wavefront manipulator (10) according to claim 10 or 11, characterized in that the coating (8) comprises optical cement and / or optical adhesive and / or a gas.

13. Wavefront manipulator (10) according to one of claims 10 to 12, characterized in that the further optical element (8, 9) is designed as a transparent cover element.

14. Optical arrangement (20) comprising an image sensor (2), characterized in that the optical arrangement (20) comprises a wavefront manipulator (10) according to one of claims 1 to 13, which is arranged in the beam path (3) after the image sensor (2).

15. Optical arrangement (20) according to claim 14, characterized in that the optical arrangement (20) is designed as a head-up display and / or as an at least partially transparent display or projection screen.

16. Optical arrangement (20) comprising an image sensor, characterized in that the optical arrangement (20) comprises a wavefront manipulator (10) according to one of claims 1 to 13, which is arranged in the beam path (3) in front of the image sensor.

Images