WO2007099456A2

WO2007099456A2 - Wavefront forming device

Info

Publication number: WO2007099456A2
Application number: PCT/IB2007/001467
Authority: WO
Inventors: Philippe Renaud-Goud
Original assignee: Seereal Technologies S.A.
Priority date: 2006-01-20
Filing date: 2007-01-15
Publication date: 2007-09-07
Also published as: TW200900886A; DE102006003738A1; WO2007099456A3

Abstract

The invention relates to a wavefront forming device (2), especially for a holographic reproduction, comprising an arrangement of mirror elements (3). Said mirror elements (3) each comprise at least one actuator (4). The respective actuator axially tilts and/or displaces the respective mirror element (3) in at least one direction. The mirror elements (3) are arranged in such a way that a wavefront (W) is directly formed by the actuation of the mirror elements (3).

Description

Wavefront shaping device

The invention relates to a wavefront shaping device, in particular for a holographic reproduction, with an arrangement of mirror elements. The invention also relates to a method of using a wavefront shaping device, in particular for holographic reproduction.

Holography is used in many areas of optical image processing for data compression and pattern recognition. In the fields of adaptive

Optics as well as pattern recognition allow modulators to modulate incident light, for example, to reduce or prevent aberrations in an optical system. As light modulators are, for example LCD, LCoS

(Liquid Crystal on Silicon), acousto-optic modulators, OASLM (Optically Addressed Spatial Light Modulator), EASLM (Electrical Addressed Spatial Light Modulator) known.

Furthermore, light modulators are known which have movable mirror elements.

For example, TG Bifano and JB Stewart, Boston University [5895-27] entitled "High-speed wavefront control using MEMS micromirrors" describes a silicon substrate-based device that transforms an incident optical wavefront by axial electro-mechanical micro mirror displacement The device comprises an array of micromirrors each mounted on electrostatic actuators, all of which are addressed by a controller which translates the mirrors axially up to half a wavelength, that is, across the reflecting surface Way, the micromirrors shape by a phase modulation from angle up to 2π optical

Wave fronts for a picture display application or in optical communication systems.

In contrast, CA 2 190 329 C describes a light modulator for modulating the intensity and phase of an incident lightwave. This has micromirrors, which are arranged on bending elements by means of electrostatic forces tilt or axially displace the micromirrors relative to their baseplate. Thus, for example, the micromirrors can be temporarily tilted by pulse width modulation for amplitude modulation by means of a control signal. Phase modulation is achieved by an electrostatic force moving micromirrors axially.

It is an object of the invention to provide a wavefront shaping device and a method for using a wavefront shaping device, in particular for a holographic reproduction, with which a better approximation accuracy or better reproduction of a wavefront can be achieved without increasing the number of pixels of the wavefront shaping device.

According to the invention, the object is achieved with a wavefront shaping device for directly simulating a wavefront, wherein the mirror elements are tiltable and axially displaceable such that an incident wavefront can be deformed into a target wavefront.

The mirror elements directly convert an incident wavefront according to a target wavefront by locally different light reflections as a result of a setting pattern. A setting pattern is understood to mean, in particular, a pattern consisting of the positions of the mirror elements, i. by tilting and / or axial displacement of the mirror elements. The adjustment pattern can be changed very quickly by moving individual or all mirror elements. The movement of a mirror element is in this case either by an axial displacement, a tilt or a combination of both.

As an incident wavefront, a wavefront is referred to, which, starting from a light source, strikes the wavefront shaping device according to the invention. A target wavefront is understood here to be a desired wavefront, which corresponds to a complex distribution of values in a certain range. This complex value distribution can be calculated, for example, by reflection of a planar wavefront on a three-dimensional object. The particular range may be, for example, when using the wavefront shaping device in a holographic Projection device be a viewer window. The viewer window would thus have a complex distribution of values. In this way, the target wavefront can be defined from the complex value distribution in the viewer window. The target wavefront is thus defined in the wavefront shaping device taking into account the shape of the incident wavefront and of optical elements in propagation direction of the wavefront after the wavefront shaping device.

Thus, for example, moving scenes with the help of known video signals as a sequence of shaped wavefronts holographically as a reconstruction in real time can be displayed.

In order to shape the incident wavefront, the mirror elements are both tilted and axially displaced by means of corresponding actuators. This means that with a local change of the target wavefront, the actuators need not move all the mirror elements. Depending on the target wavefront, only a few mirror elements can be moved. Other mirror elements, for example, perform both movements, tilting and axial displacement. In the case of changes in the target wavefront in order, for example, to represent a reconstructed scene in a certain area, the so-called reconstruction area, the setting pattern of the mirror elements is reset according to the scene. In order to follow the course of a reconstructed scene, a control device changes the activation of the actuators of the mirror elements, whereby the mirror elements assume a corresponding position or setting. The control device aligns the mirror elements in such a way that a preferably planar wavefront impinging on the mirror elements is formed directly in accordance with a target wavefront which corresponds, for example, to a single object or also to a scene having a plurality of objects.

In this way, a more accurate approximation or simulation of the phase of the required wavefront, in contrast to other previously known light modulators (SLM) is possible. The advantage of the solution according to the invention is further that computational effort is reduced by means of a fast Fourier transformation (FFT), whereby a time saving for a real-time representation when using the wavefront shaping device in a holographic reproduction device occurs. In addition, a more precise replica of the wavefront with a constant number of mirror elements causes a virtual increase in the resolution and thus, for example for a holographic reproduction, an enlarged reconstruction range or observer angle.

A combination of tilting and axial displacement of the mirror elements avoids the emergence of periodic repetitions in the reconstruction of objects of a scene which occur due to discrete scene sampling in conventional holographic display devices.

If the actuators are arranged below the mirror elements, the mirror elements can be arranged very close to one another and a high fill factor is achieved. The fill factor is the ratio of effective reflective area of all mirror elements to the total area of the wavefront shaping device. When using the wavefront shaping device in a holographic display device, a high filling factor of the mirror elements in the case of axial displacement has the advantage that the above-mentioned periodic repetitions are thereby clearly suppressed. When tilting and axial displacement of the mirror elements, however, occur no periodic repetitions, the contrast is significantly increased.

According to an additional feature of the invention, a controller may particularly precisely adjust and align the mirror elements corresponding to the target wavefront when each point of a mirror element for forming a target wavefront has a motion of at least one half wavelength. This results in a virtual increase in the resolution of the reconstruction.

It is advantageous if the mirror elements are designed as micromirrors in the form of MEMS (micro-electro-mechanical systems), since these mirrors can be adjusted very precisely electrically and moved very quickly. Likewise, these are very small and the integrated control electronics of the actuators is predominantly CMOS (complementary metal oxide semiconductor) compatible. Furthermore, the

Micromirror has a high reflectance of p> about 90%, compared to conventionally used, based on liquid crystal modulators with a reflectance of at most about 70%. This results in almost no loss of light.

In one embodiment of the invention, the wavefront shaping device is used for the holographic reconstruction of scenes in a holographic reproduction device. In this case, a reconstructed two- and / or three-dimensional scene is advantageously displayed in a large reconstruction area.

The object according to the invention is furthermore achieved by a method for using a wavefront shaping device with movable mirror elements, in particular for a holographic reproduction, wherein the mirror elements are moved into a setting pattern in such a way that the mirror elements transform an incident wavefront directly into a target wavefront.

A controller realized with actuators, depending on a target wavefront for the mirror elements, a setting pattern, which the incident wavefront after their reflection on the mirror elements directly the optical properties of a

Imprinting target wavefront. In this way, an approximation of the

Target wave front. Thus, an approximation to a target wavefront can take place or a more accurate simulation of the target wavefront than in known light modulators is possible.

An advantage of the direct shaping of the wavefront is that a computation-intensive transformation of the required wavefront into a hologram is eliminated.

In order to set a path length difference over an entire wavelength λ, because of the double path length of a propagating reflected wavefront, the at least one actuator per mirror element during axial displacement or tilting at an edge, the mirror element at least a half wavelength λ move. A device in which all points of a mirror element can perform a maximum movement of at least one half wavelength is therefore particularly suitable for realizing the invention.

According to an advantageous development of the invention, the actuators however, also move the mirror elements by a larger amount, for example one wavelength or more. As a result, the resolution of the wave front shaping is virtually increased with the same number of mirror elements, a higher accuracy is achieved and a larger reconstruction area or observer angle is generated. Consequently, it is possible with the method according to the invention to represent a reconstructed three-dimensional scene with real depth impression during reproduction in a large reconstruction area / observer angle.

In a further advantageous embodiment of the invention may further be provided that for generating different wavefronts, the mirror elements are controlled by at least one respective actuator such that at least one mirror element according to the target wavefront changes its position. Accordingly, it is not necessary that all mirror elements are tilted when changing the wavefront and moved axially by means of the actuators. All mirror elements or only a few mirror elements, for example, can only be tilted, only moved axially, perform both movements or even some

Mirror elements without changing their position form the new required wavefront.

The invention can be used for shaping wavefronts at wavelengths in each spectral range, for example for wavefront correction of imaging optical systems and lasers, in projection devices, in optical image processing or as a holographic display.

In the following, the invention will be explained in more detail with reference to embodiments. The principle of the invention is described by means of a holographic reconstruction with monochromatic light. However, the subject of the invention is also applicable to colored holographic reconstructions, which will be discussed in more detail in the respective embodiments.

The figures show:

1 shows a graphic representation of the modulation of a wavefront by means of a known phase modulating light modulator

Stringing together rectangular functions; Figure 2 is a schematic representation of an inventive

Wavefront shaping device by means of which a wavefront is formed;

FIG. 3 is a graphic representation of the shaping of a wavefront by means of the wavefront shaping device illustrated in FIG. 2;

Figure 4a shows a schematic representation of a holographic

Reproduction device with the wavefront shaping device according to the invention for the reconstruction of three-dimensional

Scenes in the top view;

FIG. 4b is an enlarged detail of the holographic display device shown in FIG. 4a;

Figure 5 shows another embodiment of the holographic

Reproduction device with a position detection system in the

Top view;

Figure 6 shows another embodiment of the holographic

Reproduction device for at least two viewers of a reconstructed

Scene in top view;

FIG. 7a shows a schematic representation of a one-dimensional wavefront shaping device;

FIG. 7b shows a schematic representation of a two-dimensional wavefront shaping device;

Figure 8 shows a way of displaying a reconstructed scene to one or more viewers; and

FIG. 9 shows another way of displaying the reconstructed scene to one or more viewers. FIG. 1 graphically illustrates a shaped wavefront of a known light modulator.

The shaped wavefront can be idealized as a juxtaposition of

Rectangular functions are displayed in a coordinate system. On the abscissa the coordinate of the wavefront and on the ordinate the phase difference modulo 2π is plotted. In this wave shaping, the wave phases can be in a range of

0 to 2π are shifted. However, a phase modulation greater than 2π is not possible. This deteriorates the approximation accuracy. As a result, with a known light modulator, only a limited approximation accuracy can be generated when scanning the wavefront.

To improve the approximation accuracy, it would be necessary to increase the resolution of the light modulator. The higher the approximation accuracy, the larger the reconstruction range can be.

In order to achieve a more accurate replica of the wavefront and an enlargement of the reconstruction range or of the observer angle, according to the invention, the target wavefronts, as shown in FIG. 2, are formed. However, this only schematically shows the formation of a wavefront. In this exemplary embodiment, mirror elements 3 of a wavefront shaping device 2 are arranged in one dimension and designed as micromirrors, in particular MEMS (Micro-Electro-Mechanical Systems) with plane mirror surfaces. Of course, the mirror elements 3 can also have other mirror surfaces. The mirror elements 3 are arranged on actuators 4 on a substrate 5 of the wavefront shaping device 2. A control device, not shown, which correspondingly addresses the actuators 4, tilts and / or shifts the mirror elements 3 axially in accordance with a target wavefront. The tilting and the axial displacement of the mirror elements 3 can be clearly seen in FIG. 2, whereby care should be taken that the mirror elements 3 are arranged very close to each other, so that the highest possible fill factor of the reflecting surfaces of the mirror elements 3 is achieved. The mirror elements 3 have a size of for example 49 .mu.m, in particular less than 49 .mu.m, at a distance from each other of about 1 micron. This achieves a high fill factor, which here is at least 98%. The wavefront shaping device 2 therefore has a multiplicity of mirror elements 3, for example 1x2000, for changing the phase of the wavefront W. Mirror elements in a one-dimensional wavefront shaping device or 2000x2000 mirror elements 3 in a two-dimensional wavefront shaping device. The mirror elements 3 are tiltable about an axis, in particular about two axes, in the case of a two-dimensional wavefront shaping device. A further, more detailed description of the mirror elements 3 and their control is dispensed with, since this is already known from the prior art, for example from CA 2 190 329 C.

To shape and change the phase of an incident wavefront W into a target wavefront, the wavefront shaping device 2 is illuminated with light rays from a light source

6 lit up. The wavefront W emanating from the light source 6 is shown here as a plane wavefront, as shown in FIGS. 1 and 2 of FIG. This level

Wavefront W hits, as indicated by arrows, at point 3 on the

Mirror elements 3 of the wavefront shaping device 2 and is corresponding to the tilting and axial displacement of the mirror elements 3 according to a

Target wave front for a scene shaped and reflected. Under item 4, the molded

Wavefront W shown after reflection on the mirror elements 3, wherein the

Actuators 4 have set a setting pattern on the mirror elements 3. The

Mirror elements 3 thus convert an incoming wavefront W into one that is necessary for the visualization of a specific three-dimensional scene.

FIG. 3 shows the phase characteristic of a wavefront formed with the displaceable and tiltable mirror elements 3. Curve pieces 3a, 3b, 3c, 3d and 3e correspond to the required position of the mirror elements 3. It is possible that, due to the course of the phase function to be represented, the edge points of the corresponding mirror element 3 have a phase difference greater than 2π, e.g. the curve piece 3b. Due to the combination of tilting and axial displacement of the mirror elements 3, a substantially more accurate approach to a target wavefront than in known solutions, such as light modulation devices according to FIG. 1, is possible. As a result, the resolution can be increased virtually and thus the reconstruction area or the observer angle can be increased.

FIG. 4 a shows a holographic display device 1 shown in principle for the reconstruction of advantageously three-dimensional scenes in plan view. To the a better understanding, the holographic display device 1 in Figure 4a and shown in simplified form in the following figures as a transmissive device. In the following, the basic structure will be described first. As can be seen in the exemplary embodiment, the wavefront shaping device 2 is a one-dimensional wavefront shaping device, which is arranged vertically here. The wavefront shaping device 2 is illuminated by a lighting device 7 with a light source 8, which emits sufficiently coherent light and represents a line light source. Under sufficiently coherent light here light is understood, which is capable of interfering with the representation of a three-dimensional scene. As the light source 8 of the illumination device 7 laser diodes, DPSS laser (diode pumped solid-state laser) or other lasers can be used. Even light sources with sufficient coherence can be used. However, such light sources should be filtered to achieve a required degree of coherence. The holographic display device 1 further includes an optical system 9. This optical system 9 has an imaging means 10 and a screen 11. Of course, the optical system 5 can also have further optical elements, as can be seen and described, for example, in the following explanations. The screen 11 is advantageously designed as a mirror, in particular as a concave mirror. Of course, the screen 11 may also be another imaging optical element, such as a lens, as shown here. If the screen 11 is a concave mirror, there is the advantage that the extension of the optical structure of the holographic display device 1 is substantially reduced as compared with a lens-only transmissive device. However, the screen 11 should not have a scattering surface so that a wavefront 12 emanating from the wavefront shaping device 2 is not destroyed. If a two-dimensional representation of the reconstructed scene is desired, the screen 11 may also have a diffusing surface. The imaging means 10 is also implemented as a mirror or lens. The monochromatic wavefront 12, which is reflected and shaped by the wavefront shaping device 2, is imaged onto a deflection element 13 by means of lens elements 19 and 20 in order to reconstruct a three-dimensional scene. Such a deflection element 13 may be a galvanometer scanner, a piezo scanner, a resonance scanner, a polygon scanner, a micromirror arrangement or a similar device. The deflector 13 causes an optical deflection of the wavefront 12 in the direction perpendicular to the Wavefront shaping device 2 to produce a two-dimensional wavefront 14. The two-dimensional wavefront 14 is formed by the deflection of a series of parallel one-dimensional wave fronts 14 ', 14 "and 14'" and so on. The optical system 9 then images the shaped two-dimensional wavefront 14 into a viewer's virtual window 15 of a viewer plane 16 in which an observer's eye is to observe the reconstructed scene. The sufficiently coherent light of the light source 8 is displayed on the screen 11. A Fourier-transformed FT of the wavefront 12 is formed between the lens elements 19 and 20 in the image-side focal plane. The imaging means 10 of the optical system 9 then images the Fourier transform FT in the image-side focal plane 17 on the screen 11. The reconstructed scene may then be viewed by the viewer in an enlarged reconstruction area 18 which is frusto-conical between the virtual viewer window 15 and the screen 11, or at an enlarged viewer angle, respectively. Due to the presence of a high fill factor of the mirror elements 3 of the wavefront shaping device 2, there are no periodic repetitions of the reconstructed scene in the observer plane 16.

Since the mirror elements 3 of the wavefront shaping device 2 can be tilted by means of the actuators 4, the shaped wavefront 12 can be influenced such that the reconstruction of the three-dimensional scene takes place in the zeroth diffraction order. This is particularly advantageous because in the zeroth diffraction order the brightness or the intensity of the light is greatest.

It is also possible to integrate the deflection element 13 directly into the wavefront shaping device 2. This means that the wavefront shaping device 2 forms the plane wavefront W, as already described above, by means of the mirror elements 3. However, to generate the two-dimensional wavefront 14, the wavefront shaping device 2 is moved as a whole system. The lens elements 19 and 20 can be omitted in this case. The wavefront shaping device 2 is then arranged in the region of the deflecting element 13, that is to say in the object-side focal plane of the imaging means 10. A beam splitter element 21 for color reconstruction may then be positioned, for example, between the wavefront shaping device 2 and the imaging means 10. Furthermore, it is also possible, instead of the movement or tilting of the whole Systems only the arrangement of the mirror elements 3 as a whole unit for generating the two-dimensional wavefront 14 to move. In this way, the holographic reproduction device 1 can be made more compact in overall construction.

In addition, in the beam path of the holographic display device 1, the lens elements 19 and 20 may be arranged, which, as can be seen here at the individual focal lengths, for the reduction of aberrations have an equal refractive power. However, the lens elements 19 and 20 may also have different refractive powers or focal lengths in order to change or optimize the size of the one-dimensional wavefront 12 on the deflection element 13 when it is arranged between the wavefront shaping device 2 and the optical system 9. The lens elements 19 and 20 have a further advantage in this case. They then ensure that the shaped wavefront 12 reflected by the wavefront shaping device 2 is imaged onto the deflection element 13 for generating the two-dimensional wavefront 14. To image the wavefront 12 onto the deflection element 13, an afocal system, represented by the lens elements 19 and 20, can be used. In the image-side focal plane of the lens element 19, the Fourier transform FT of the wavefront 12 is formed. By means of the lens element 20 and the imaging means 10, the Fourier transform FT is imaged onto the screen 11.

However, the deflecting element 13 can also be arranged between the light source 8 and the wavefront shaping device 2. This has the advantage that as a result errors in the shaping of the two-dimensional wavefront 14 are largely prevented or reduced, since the planar wavefront W impinging on the wavefront shaping device 2 has not yet been coded.

A colored reconstruction of the three-dimensional scene is also possible with the holographic display device 1. 4a, the beam splitter element 21, in particular a prism block, is provided in the beam direction in front of the imaging means 10. The beam splitter element 21, which is advantageously designed here as an X prism with dichroic layers, splits red, green and blue light into three separate wavefronts or adds the separate wavefronts to one common wave front together. The color reconstruction of the scene takes place simultaneously in the three basic colors RGB (red-green-blue). The beam splitter element 21 is arranged in this embodiment between the lens elements 19 and 20, wherein it may of course also be arranged at a different position in the holographic display device 1. Likewise, another beam splitter element can be provided.

FIG. 4b shows an enlarged detail of the beam splitter element 21 of FIG. 4a. In this case, three wavefront shaping devices 2R, 2G and 2B are provided for each of the three primary colors RGB for the simultaneous colored reconstruction of the three-dimensional scene. The three wavefront shaping devices 2R, 2G and 2B are illuminated by three light sources 8R, 8G and 8B. The beam splitter element 21, after forming individual associated wavefronts 12R, 12G and 12B on the wavefront forming devices 2R, 2G and 2B, merges them to continue on the lens element 20. It is also possible that only one light source, in particular a white light source, is used for color reconstruction. Here, too, the beam splitter element 21 is arranged between the lens elements 19 and 20. However, a semitransparent mirror is arranged between the beam splitter element 21 and the lens element 20. To illuminate the three wavefront shaping devices 2R, 2G, 2B and shaping the wavefronts, the light from the light source is directed onto the semitransparent mirror and from there by means of the beam splitter element 21 to the three wavefront forming devices 2R, 2G, 2B, wherein the beam splitter element 21, the light in the three monochromatic wavefronts 12R, 12G, 12B splitted. Furthermore, it is also possible to provide not three, but only a single Wellenfrontformvorrichtung for color reconstruction, this possibility is not shown. This wavefront shaping device can be illuminated with a light source which has three different-colored light-emitting diodes (LED) or a white-light LED. In addition, however, at least one optical element, for example an acousto-optic element, is required which, for example, transmits the wavefronts to the wavefront shaping device at a different angle of incidence.

Instead of the above-described color representation with three simultaneously operating wavefront shaping devices 2R, 2G, 2B is also a sequential color representation with at least one wavefront shaping device possible.

The holographic reproduction device 1 described above has been described only for an eye of an observer. For a pair of eyes of the observer, it makes sense to provide a second wavefront shaping device 2. The optical elements of the existing holographic display device 1 can continue to be used. If the observer is now in the observer plane 16 and is looking through the observer window 15, he can observe the reconstructed three-dimensional scene in the reconstruction area 18, the reconstructed three-dimensional scene being created in front of, on or behind the screen 11. However, it is also possible to represent the reconstructed scene with only one single wavefront shaping device 2 to one eye pair of the observer, the wavefront shaping device 2 being arranged horizontally.

FIG. 5 shows a further exemplary embodiment of the holographic reproduction device 1. The design of the reproduction device 1 basically corresponds to that of FIG. 4a. Therefore, like parts have the same reference numerals. The display device 1 also has a position detection system 22 for determining changes in an eye position of a viewer in the observer plane 16. The position detection system 22 may be, for example, a camera. For tracking the virtual observer window 15 when changing the eye position of the viewer, a deflection means 23 between the imaging means 10 and the screen 11, in particular in the image-side focal plane of the imaging means 10, is arranged. The deflection means 23 is individually controllable and designed as a mirror. For tracking the observer window 15, a very precise deflection means is needed. For this reason, the deflection means 23 may be, for example, a galvanometer scanner. Of course, it is also possible to use other deflection means, such as MEMS arrangements, piezo scanners or the like. Likewise, the deflection means 23 can deflect in at least one of the directions horizontally and / or vertically. That is, the deflection means 23 in one-dimensional embodiment, either horizontally or vertically, the observer window 15 tracks. In a two-dimensional embodiment of the deflection means 23, the viewer window 15 in both directions, horizontal and vertically, be tracked. For this purpose, the deflection means 23 may be designed as an xy-galvanometer scanner, or it is also possible to use two successively arranged galvanometer scanners, one for a horizontal and one for a vertical tracking. Furthermore, a second imaging means 24 connected downstream of the deflection means 23 in the light direction is provided. Since the magnification for imaging on the screen 11 must be very large, the second imaging means 24 may be implemented as a lens system as well as a lens system for reducing aberrations.

In the following, the reconstruction of the three-dimensional scene will be described with reference to this embodiment. The wavefront W emitted by the light source 8 is incident on the wavefront shaping device 2, which reflects the shaped wavefront 12. After reflection, the shaped wavefront 12 passes through the lens elements 19 and 20 and is imaged by them onto the deflection element 13. At the same time, by means of the lens element 19, the Fourier transform FT of the wavefront 12 is formed in the image-side focal plane of the lens element 19. After the formation of the two-dimensional shaped wavefront 14, it strikes the deflection means 23 after passing through the imaging means 10 Position detection system 22 this movement can be detected. For tracking the observer window 15, the deflection means 23 can then be controlled with the position detection system 22. By means of the imaging means 10 and 24, an image of the shaped two-dimensional wavefront 14 is formed in an image-side focal plane 25 of the second imaging means 24. This two-dimensional image in the focal plane 25 is then imaged via the screen 11 into the observer window 15. At the same time, the image of the Fourier transform FT is formed in a image-side focal plane 26 of the imaging means 10. The second imaging means 24 then maps the mapping of the Fourier transform FT onto the screen 11. For a pair of eyes of the beholder, it is also useful here to provide a second wavefront shaping device 2. If the observer is now in the observer plane 16 and is looking through the observer window 15, he can observe the reconstructed three-dimensional scene in the reconstruction area 18, the reconstructed three-dimensional scene being created in front of, on or behind the screen 11. But it is also possible here, only with a single wavefront shaping device 2 a pair of eyes of the viewer, the reconstructed Scene represent, wherein the wavefront shaping device 2 is arranged horizontally again.

A colored reconstruction of the three-dimensional scene can be carried out according to the examples described above by means of the beam splitter element 21.

The illumination device 7 with the light source 8 can also be arranged at an arbitrary position in the holographic reproduction device 1. If, for example, the wavefront shaping device 2 is designed to be reflective, then the illumination device 7 can also be arranged in such a way that the emitted wavefront W is transmitted via a deflection element, e.g. a deflection mirror or a semitransparent mirror to which wavefront shaping device 2 is guided. It is advantageous if the light source 8 is imaged onto a Fourier plane, wherein the deflection element is arranged in the Fourier plane. In this case, at least one optical element, such as a lens, mirror or the like, may be provided between the deflection element and the wavefront shaping device 2. With reference to FIG. 5, such a deflection element can be arranged at the location of the beam splitter element 21, whereby the beam splitter element 21 can then be provided between the lens element 19 and the deflection element or between the deflection element and the lens element 20. In this way, the holographic display device 1 can be made more compact in structure.

FIG. 6 shows a further exemplary embodiment of the holographic reproduction device 1, the structure here basically corresponding to the construction of the reproduction device 1 according to FIG. Therefore, the same parts have the same reference numerals here as well. In contrast to FIGS. 4 a and 5, the reproduction device 1 according to FIG. 6 is suitable for a plurality of viewers. For a simplified illustration, only the beam paths for two observers and only one one-dimensional wavefront per viewer are shown. In principle, however, more than two observers can observe the reconstructed three-dimensional scene. The viewer window with the letter R stands for the right eye and the viewer window with the letter L for each of the left eye of a viewer. To represent the reconstructed three-dimensional scene are here two wavefront shaping devices 2 are shown in the holographic display device 1. These two wavefront shaping devices 2 are illuminated by at least one illumination device 7 with at least one light source 8. The light sources 8 are independent of each other with different light incidence angles. The number of light sources 8 per wavefront shaping device 2 is dependent on the number of viewers of the reconstructed scene and is determined by them. For two or more observers, a single wavefront shaping device 2 is used for each of the same observer window, that is to say for the right eyes or for the left eyes of the observer. The light sources 8 illuminate the mirror elements 3 of the wavefront shaping device 2 with sufficiently coherent light in respectively different angles of incidence. The angles of incidence of the light of the light sources 8 for the observer windows 15R and 15L of the eye pair of a viewer are always almost identical. That is, the incident angle of the light sources 8 for generating shaped wavefronts 12L and 27L are different for the viewer windows 15L and 28L. The screen 11, the deflector 13, the lens elements 19 and 20 and the imaging means 10 and 24 may be used for both wavefront shaping devices 2.

In contrast to FIG. 5, two deflection means 23 are provided for tracking at least two, in this case three, observer windows 15R, 15L and 28L corresponding to the respective eye position of the observer. The number of deflection means 23 is dependent on the number of viewers. This means that only one deflection means 23 is used per viewer for both eyes, here observer windows 15R and 15L. In the beam direction behind the deflection means 23, the second imaging means 24 is arranged in connection with a focusing element 30. The second imaging means 24 is here designed as a lenticular serving to collimate the wavefronts 14R and 14L, wherein both wavefronts 14R and 14L for the left and right eyes are guided by a lenticle of the second imaging means 24 corresponding to the deflection means 23. The focusing element 30 is used after the passage of the two wavefronts 14R and 14L through the corresponding lenticule of the second imaging means 24 for overlapping and focusing the wavefronts 14R and 14L on the screen 11. Another deflection means 23 is provided for tracking the viewer window 28L for a two-dimensional wavefront 29L , A third illustrated deflection means 23 serves to serve a third observer, although more than three observers can observe the reconstructed scene. The number of lenticules of the second imaging means 24 corresponds to the number of deflection means 23 in the display device 1. To reduce aberrations, the focusing element 30 can be replaced by a more complex arrangement of lenses. For example, the focusing element 30 may be formed as achromatic. It is also possible to provide the second imaging means 24 and the focusing element 30 as a single lenticular in the display device 1, for example.

The reconstructed three-dimensional scene arises here, as already described under FIG. 5, except that in this exemplary embodiment the holographic display device 1 is intended for a plurality of viewers and therefore the observer windows 15R, 15L and 28L are tracked via a plurality of deflection means 23. With the holographic display device 1 shown here, it is possible to operate three viewer windows simultaneously.

Instead of using light sources 8 which emit sufficiently coherent light which impinges on the wavefront shaping devices 2 at different angles of incidence, it is also possible to provide a single light source 8 for each wavefront shaping device 2. The duplication of the wavefronts then takes place after shaping and reflection at the mirror elements 3 of the wavefront shaping device 2. This can be done, for example, in the region of the deflecting element 13 with the aid of a grating element. The advantage of this solution is that phase defects of wavefronts of the individual light sources 8 on the wavefront shaping devices 2 can be corrected.

The light sources 8 can also be generated by a primary light source, not shown here, with the aid of at least one optical element.

With reference to FIGS. 5 and 6, the deflection means 23, which is designed as a mirror, in particular as a galvanometer scanner, can be provided with a light-scattering layer. The deflection means 23 can thus be designed as a mirror which scatters in the horizontal direction. The light-scattering layer can be designed, for example, as a film. The spread of the scattered light or the scattered wavefront must be perpendicular to the formed one-dimensional wavefront. Since coherence is required in a holographic reconstruction, it must not be disturbed by introducing a light-scattering layer. However, this makes it possible to achieve an enlargement or enlargement of the observer windows 15, 15R, 15L ₁ 28L in a noncoherent direction, wherein the observer windows 15, 15R, 15L, 28L are delimited in the other direction by the extent of the diffraction orders. It is particularly advantageous if the wavefront shaping device 2 is arranged horizontally. In this way, a widening of the individual viewer windows 15, 15R, 15L, 28L can be made possible in the vertical, non-coherent direction. Therefore, with this arrangement of the wavefront molding apparatus 2, since the observer windows 15, 15R, 15L, 28L are large in that direction, it is no longer necessary to vertically adjust the viewer windows 15, 15R, 15L, 28L according to the vertical position of the observer. It is also possible to apply the light-scattering layer on the screen 11, which then serves not only for imaging and display, but also scatters the Fourier transform of the wavefront in a non-coherent direction.

The exemplary embodiments of the invention according to FIGS. 4 a, 5 and 6 always relate to at least one one-dimensional wavefront shaping device 2 for shaping at least one incident wavefront. Such a one-dimensional wavefront shaping device 2 is shown in a perspective view in FIG. 7a. As shown, the mirror elements 3 are arranged as a row or column on the substrate 5. The actuators are not shown here.

As FIG. 7 b shows, however, the invention can also be realized with a two-dimensional wavefront shaping device 2. In this case, the deflection element is no longer necessary for generating a two-dimensional wavefront. In this exemplary embodiment, the mirror elements 3 are arranged in a plurality of rows or columns on the substrate 5. The mirror elements 3 of the two-dimensional wavefront shaping device 2 can be tilted and / or axially displaced about one or even two axes by means of at least one actuator. When tilting by 2 axes, the reconstruction area can be enlarged in the vertical and horizontal direction. FIGS. 8 and 9 describe different possibilities for the temporal multiplexing of the rows or columns S of the shaped wavefront 12 in the realization of two-dimensional wavefronts of a partial image of the reconstructed three-dimensional scene for two or more observers B1 and B2 by the deflection element 13 in interaction with FIG of the one-dimensional wavefront shaping device 2. According to FIG. 8, the two-dimensional wavefront of a partial image is completely built up first for the viewer B1 and then for the viewer B2. According to FIG. 9, the rows or columns of the shaped wavefront of a partial image belonging to the individual observers B1 and B2 are displayed alternately successively.

Possible fields of use of the wavefront shaping device 2 and the holographic reproduction device 1 can be displays for a two-dimensional and / or three-dimensional representation for the private and work areas, such as for example computers, television, electronic games, the automotive industry for displaying information or entertainment, medical technology, in particular for minimally invasive surgery or the spatial representation of tomographic data or for military technology for the representation of terrain profiles. Of course, the present wavefront shaping device 2 and the display device 1 can also be used in other areas not mentioned here.

Claims

claims

A wavefront shaping device with an arrangement of mirror elements for directly simulating a wavefront, wherein the mirror elements (3) are tiltable and axially displaceable such that an incident wavefront (W) can be deformed into a target wavefront.

2. wavefront shaping device according to claim 1, characterized in that the mirror elements (3) for a phase change of the incident wavefront (W) are tilted.

3. wavefront shaping device according to claim 1, characterized in that the mirror elements (3) for a phase change of the incident wavefront (W) are axially displaceable.

4. wavefront shaping device according to claim 1, characterized in that the mirror elements (3) are arranged one-dimensionally.

5. wavefront shaping device according to claim 4, characterized by having a deflection element for generating a two-dimensional wavefront.

6. wavefront shaping device according to claim 1, characterized in that the mirror elements (3) are arranged two-dimensionally.

7. Wellenfrontformvorrichtung according to claim 1, characterized in that at least one actuator (4) between each mirror element (3) and a substrate (5) is arranged for driving.

8. Wellenfrontformvorrichtung according to claim 1, characterized in that each point of a mirror element (3) for forming a Zielwellenfront a

Movement of at least half a wavelength.

9. wavefront shaping device according to claim 1, characterized in that the mirror elements (3) are arranged to each other such that a filling factor of at least 98% is achievable.

The lO.Wellenfrontformvorrichtung according to claim 1, characterized in that the

Mirror elements (3) have flat mirror surfaces.

H .Wellenfrontformvorrichtung according to claim 4, characterized in that the mirror elements (3) are each tiltable about an axis which is perpendicular to the arrangement direction of the mirror elements (3).

12.Wellenfrontformvorrichtung according to claim 6, characterized in that the mirror elements (3) are tiltable about at least one axis.

13.Wellenfrontformvorrichtung according to claim 1, characterized in that the

Mirror elements (3) are designed as micromirrors.

14.Wellenfrontformvorrichtung according to claim 1, for holographic

Reconstruct scenes.

15. A method for using a wavefront shaping device with movable mirror elements, wherein the mirror elements (3) in such a way

Setting patterns are moved so that the mirror elements transform an incident wavefront (W) directly into a target wavefront.

16. The method according to claim 15, characterized in that for shaping the wavefront (W), the mirror elements (3) are tilted according to the target wavefront.

17. The method according to claim 15, characterized in that for shaping the wavefront (W), the mirror elements (3) are axially displaced according to the target wavefront.

18. The method according to claim 15, characterized in that at least one actuator in each case a mirror element (3) drives, wherein the mirror element (3) is adjusted and aligned according to the target wavefront.

19. The method according to claim 15, characterized in that for generating different wavefronts, the mirror elements (3) by means of at least one respective actuator (4) are driven such that at least one Spiegeleiement (3) according to the target wavefront changes its position.

20. The method according to claim 15, characterized in that a three-dimensional scene, in particular a three-dimensional moving scene, holographically displayed.

21. The method according to claim 20, characterized in that the three-dimensional scene is displayed in real time.