Patent Application
20100033784
The present invention relates to a holographic projection device for the reconstruction of scenes, said device comprising at least one light source which emits sufficiently coherent light which is used to generate a wave front, and at least one two-dimensional light modulator device which consists of individual modulation elements. The invention further relates to a method for the holographic reconstruction of scenes.
It is commonly known to use holographic techniques in order to reproduce a real three-dimensional scene of an object, said scene containing all depth information which is used by the human brain in image processing. Holography is a technique for recording and later reproduction of amplitude and phase distributions of a wave front. More precisely, an interference pattern of coherent light reflected on an object and light which comes directly from a light source is recorded on a recording medium, such as a photographic plate. If the interference pattern, which is also known as a hologram, is illuminated with coherent light, a three-dimensional scene will appear in a space. Typically, a real three-dimensional object is used to generate a hologram using known methods and techniques; thus generated holograms are known as true holograms. However, computer-generated holograms (CGH) may be used as well.
Usually, the reconstructed scene is viewed directly, i.e. the observer looks on to the computer-generated hologram, for example, which consists of regularly arranged pixels which have been encoded in accordance with the hologram values. Due to the discrete recording and because of the effects of deflection, the reconstruction of the CGH is only possible within one periodicity interval of the deflection spectrum, which is defined by the resolution of the CGH-carrying medium. The reconstruction is typically repeated showing irregularities in adjacent periodicity intervals.
Reversible CGH recording media include spatial light modulators, such as LCD (liquid crystal displays), LCoS (liquid crystal on silicon), OASLM (optically addressed spatial light modulators) etc., which modulate the phase and amplitude of incident light. Further, it is known that MEMS-based light modulators can be used to modulate phase and/or amplitude of light. Optical elements which transform the CGH into the desired plane are also often used for reconstructing two- and three-dimensional scenes.
U.S. Pat. No. 5,172,251, for example, discloses a projection device with a one-dimensional light modulator for reconstructing a three-dimensional scene. The light modulator is an acousto-optic modulator which is controlled by modulation signals of a data processing system, thus encoding a one-dimensional hologram. The reconstruction is diminished with the help of several optical elements, so to increase the viewing angle in the horizontal direction. A horizontal scanner continuously combines partial holograms of the scene and balances the movement of the partial holograms along the modulator. The horizontal scanner is synchronised with the speed of the acoustic wave, so that the scanned areas of the original image from the modulator appear fixed in the reconstructed scene. In addition, a vertical scanner is provided in order to position in the vertical direction the horizontal one-dimensional holograms.
However, because that projection device uses an acousto-optic modulator (AOM), it exhibits the disadvantage of requiring additional elements such as the horizontal scanner which aims to balance the signal movement. This makes the design rather difficult and complex. Moreover, the modulator must work at high speed. Another drawback is the small aperture of the AOM, which requires sub-holograms to be stringed together.
EP 1 467 263 A1 also discloses a holographic display device for reconstructing a three-dimensional scene. The display device consists of a reflective light modulator, a beam splitter for projecting a hologram, a light source, a shutter, a field lens and a collimator lens. The hologram is generated on a computer using three-dimensional object information and then displayed on the light modulator. The light modulator is then illuminated with light emitted by the light source and projected through the beam splitter, such that a three-dimensional scene is reconstructed. The reconstructed scene is thereby created around the field lens. A colour reconstruction of the scene, where the colour light sources are disposed close to each other, is also mentioned. These light sources simultaneously emit light of different wavelengths.
The above described holographic display device exhibits the following disadvantages. The size of the reconstructed scene is limited by the size of the filed lens. Further, the observer of the reconstructed scene only has limited freedom of movement; a tracking facility for an observer window for an observer eye has not been proposed. Moreover, the diffraction orders recur periodically in the Fourier plane.
Now, the object of this invention is to provide a device and method for holographic reconstruction of scenes which prevails over the afore-mentioned disadvantages of the prior art, said device and method being able to deliver reconstructions of two- and three-dimensional scenes at shorter computing time and in a larger observer range compared with conventional holographic display devices, even if one or multiple observers move.
According to the present invention, this object is solved by providing at least one scanning system and one projection system, where the scanning system comprises at least one scanning element, and where the light modulator device and the scanning element are combined such that the light emitted by the scanning element scans one after another one-dimensional arrangements of modulation elements of the two-dimensional light modulator device, where the scanning system is designed such that it sequentially creates a wave front which contains the information required for reconstructing a wave front, and where the projection system is designed such that it subsequently reconstructs the scene.
The inventive holographic projection device comprises at least one light source which emits coherent light, and at least one light modulator device. The light modulator device comprises modulation elements, so-called pixels, which encode the scene to be reconstructed. Further, the light modulator device is of two-dimensional design. The holographic projection device further comprises at least one scanning system and one projection system. By dividing the inventive holographic projection device into two independent systems, namely a scanning system and a projection system, it is possible to replace the currently used projection system or scanning system for a different desired or required system easily, quickly and uncomplicatedly. A scanning element contained in the holographic projection device, specifically in the scanning system, is combined with the light modulator device such that the scanning element scans with the coherent light one after another one-dimensional arrangements of modulation elements, i.e. only one line or one column of the two-dimensional light modulator device, at a time. This means that the entire two-dimensional light modulator device is not scanned at once, but always one one-dimensional arrangement of modulation elements only at a time. The individual one-dimensional arrangements are scanned one after another, as already mentioned above. The scanning system is therein provided for sequentially generating a wave front which contains the information required for reconstructing a scene. The projection system is intended for reconstructing the scene subsequently. The scanning element used can be a resonance scanner, MEMS (micro electro mechanical system), piezo mirror, galvanometer scanner or similar element.
This way a holographic projection device for simple and quick reconstruction of two- and three-dimensional scenes in a large reconstruction space is provided. The time needed for hologram computation is significantly shortened because a one-dimensional fast Fourier transformation is performed only instead of a much more complex two-dimensional fast Fourier transformation. Conventional two-dimensional light modulator devices can preferably be used in the inventive projection device. It is thus not necessary anymore to use very fast two-dimensional light modulator devices. All modulation elements of the two-dimensional light modulator device are controlled in accordance with the target wave front, so that each one-dimensional arrangement, i.e. line or column, is scanned with sufficiently coherent light by the scanning element. This way, the light modulator device can be scanned faster without the need to increase the speed of controlling the light modulator device itself. In the inventive projection device, the one-dimensional arrangement, i.e. line or column, can be recoded while a different one-dimensional arrangement of the two-dimensional light modulator device is scanned, whereas in a one-dimensional light modulator device the modulation elements must be recoded after each scan.
It is also possible to use less conventional two-dimensional light modulator devices, such as a light modulator device based on micro-mirror elements, where for example the micro-mirror elements can be displaced axially and tilted around an axis. In such a light modulator device, the advantage is that the enlargement of the observer window in one direction is based on the design of the light modulator device, and the enlargement in the other direction is based on the special construction of the inventive projection device. Such light modulator devices can be, for example, MEMS, membrane mirror systems, OASLM or AOM (acousto-optic modulators).
Further, the light modulator device used is preferably an expanded spatial light modulator device and no limited modulator, such as an acousto-optic modulator, which makes redundant additional elements such as the horizontal scanner described in U.S. Pat. No. 5,172,251 and their arrangement within the projection device.
It is advantageous if the holographic projection device is anamorphic, i.e. if it exhibits different magnification in two directions which are perpendicular to each-other and perpendicular to the direction of light propagation. This is important for the wave front modulated by the modulation elements to propagate to, i.e. to be projected to, the same position in an observer plane, for example to a virtual observer window where at least one observer eye is located, if the light modulator device is scanned line by line. This helps to prevent the light from being vignetted. The same applies accordingly if the light modulator device is scanned column by column. Another advantage is that an enlargement of the observer window in the scanning direction, which is also referred to as the non-coherent direction below, becomes possible, even if such great magnification in the other direction, also referred to as the coherent direction below, is limited by the scanning theory.
According to another preferred embodiment of the invention, a reproduction scale and screen size can be chosen such that a periodic continuation of diffraction orders of the Fourier transform lies outside the screen. This exhibits the advantage that the periodic continuation of the diffraction orders is displaced out of the screen, and only one period is visible on the screen. This means that an observer of the reconstructed scene does not perceive the periodic continuation of the reconstruction in the various diffraction orders. The image quality is thus considerably improved compared with prior art devices.
In order to make available a virtual observer window for one or multiple observers in a large observer range, a position detection system may be used to detect eye positions of at least one observer in an observer plane when viewing the reconstructed scene.
The position detection system detects and tracks changes in the eye positions of the observer or observers who view the reconstructed scene, whereupon the reconstructed scene is encoded such that is becomes visible depending on the change in the eye position of the observer(s) in horizontal, vertical and/or axial direction. This is particularly advantageous in order to be able to update the position and/or content of the reconstructed scene according to a changed eye position. Then, the virtual observer window can be tracked according to the new eye position.
At least one deflection element may preferably be used to track a virtual observer window in the observer plane according to a change in the eye positions of the observer. Such deflection elements can be mechanical, electric, magnetic or optical elements, such as galvanometer mirrors, MEMS or acousto-optic elements.
The object of the invention is further solved by a method for the holographic reconstruction of scenes, where at least one light source illuminates at least one two-dimensional light modulator device containing modulation elements with sufficiently coherent light, where only one-dimensional arrangements of modulation elements of the two-dimensional light modulator device are scanned one after another by the scanning element, so that multiple one-dimensional wave fronts are generated, where a wave front which contains the information required for reconstructing a scene is generated sequentially with the help of the one-dimensional wave fronts, and whereupon a scene is reconstructed.
According to the novel method, sufficiently coherent light, which is emitted by an illumination device, is directed on to a scanning element for holographic reconstruction of two- and/or three-dimensional scenes. The scanning element scans with coherent light individual one-dimensional arrangements of modulation elements of a two-dimensional light modulator device one after another. This way, multiple one-dimensional wave fronts are generated one after another. Each one-dimensional wave front only represents a part of a scene, in particular a three-dimensional scene, to be reconstructed. A wave front which contains the information required for reconstructing a scene is generated sequentially with the help of the one-dimensional wave fronts, in order to subsequently reconstruct a scene, in particular a three-dimensional scene. Scanning only one line or column of the two-dimensional light modulator device at a time makes it possible to avoid great computational load and to reduce the time needed for computation, because a one-dimensional Fourier transform must be computed and encoded only.
According to a preferred embodiment of the present invention, one Fourier transform of the light emitted by the light source and modulated by the light modulator device per one-dimensional arrangement of modulation elements may be projected on to an optical element, which serves as a screen, where at least this optical element projects a wave front modulated with the help of the light modulator device into a virtual observer window. However, it is also possible that the individual Fourier transforms are projected into the virtual observer window, and not on to the screen. Accordingly, the modulated wave fronts are projected on to the screen.
Further embodiments of the invention are defined by the other dependent claims. Embodiments of the present invention will be explained in detail below and illustrated in conjunction with the accompanying drawings. The principle of the invention will be explained based on a holographic reconstruction with monochromatic light. However, it appears to those skilled in the art that this invention may as well be applied to colour holographic reconstructions, as indicated in the description of the individual embodiments.
a shows schematically an inventive scanning system and illustrates the direction of propagation of the one-dimensional wave fronts and the direction of light propagation (coherent direction).
a shows schematically an inventive scanning system and illustrates the scanning direction and the direction of light propagation (non-coherent direction).
a show details of the inventive scanning system which illustrate how the to 4c light modulator device is scanned by a rotating scanning element.
a show details of the projection system and illustrate an overlapping of to 6e two light channels with at least one projection means.
a show schematically a simplified scanning system according to the and 9b present invention in the coherent and non-coherent direction.
a show schematically an inventive, very compact holographic projection and 11b device in the coherent and non-coherent direction.
a show schematically a second possibility of the functional principle of and 14b the inventive holographic projection device, where only the scanning system is shown in the coherent and non-coherent direction.
Now, the design of the inventive holographic projection device and the reconstruction of a scene, preferably a three-dimensional scene, will be described.
This Figure shows in detail how the light modulator device 3 is scanned by a scanning element (not shown). The scanning element will be shown in detail in
Before the light modulator device 3 is scanned the first time by the scanning element, the modulation elements 4 are addressed and brought to the required modulation position. The individual one-dimensional arrangements of modulation elements 4 can then be scanned as described above. The modulation elements 4 can be readdressed after having fully scanned all one-dimensional arrangements in the light modulator device 3. Consequently, the modulation elements 4 must only be addressed again after having scanned all one-dimensional arrangements, whereby the switching time of the modulation elements 4 is reduced. Alternatively, it is also possible to readdress each one-dimensional arrangement immediately after it has been scanned. This option also provides the benefit of time saving. This is particularly advantageous if a light modulator device 3 based on micro mirrors is used for example, where all modulation elements 4 are mirror elements which can either only be displaced axially or both be displaced axially and tilted around an axis.
a and 2b only show a sub-system of the holographic projection device, where the optical path is a non-folded optical path. The embodiments described below also show non-folded optical paths. This sub-system is called the scanning system AS and contains the illumination device 1 with light source 2, the scanning element 5, the light modulator device 3 and projection elements 6, 7, 8, 9, 9′ and 10. The projection element 7 contains lens elements 7a and 7b, the projection element 8 contains lens elements 8a and 8b, and the projection element 10 contains lens elements 10a, 10b and 10c. The projection elements 6, 7, 8, 9, 9′ and 10 can be lenses, in particular cylindrical lenses, spherical lenses, corrected cylindrical or spherical lenses, diffractive optical elements (DOE), Fresnel lenses, but also mirrors or arrangements of several such elements. Further, the projection elements 6, 7, 8, 9, 9′ and 10 may also be disposed off-axis, which facilitates to reduce aberrations, such as field curvature. The holographic projection device is anamorphic, i.e. the projection systems and thus the degrees of magnification in two directions of the projection device which are perpendicular to each other are different. This is why it must be noted that
Now, the functional principle of the scanning system AS in the coherent direction is described with reference to
While the wave front WF is projected, a Fourier transform FT is generated at the same time in the plane 11′. If a reflective light modulator device 3 is used, the planes 11 and 11′ coincide so to form one and the same plane. It is possible to dispose a deflection element, for example a mirror, in plane 11′ in order to prevent the light on the way to the light modulator device 3 from overlapping with the light on the way back. Further, such deflection element may also be provided if a transmissive light modulator device 3 is used, for reasons of compactness. The Fourier transform FT is projected by the lens element 10a as a collimated bundle of rays into plane 12. In conjunction with a reflective light modulator device 3, the projection of the wave front WF into plane 11′ is provided preferably in order to reduce aberrations. However, this projection is not necessarily required id a transmissive light modulator device 3 is used. Because this embodiment and any other embodiments described below are only shown schematically, it must be noted that the projection elements 9 and 9′ are represented by one single projection element, because the light modulator device 3 is of a reflective type, so that the modulated wave front WF is reflected back into plane 11′ (=11). Planes 11 and 11′ are thus one and the same plane.
In the non-coherent direction, shown in
The scanning element 5 can of course also be a scanning prism.
The scanning element 60 rotates around the rotation axis such that the incident light, here indicated through the light beams 50, 51 and 52, after its passage through the scanning element 60 is offset parallel to the optical axis OA of the scanning system AS. If the light beams 50, 51 and 52 impinge on a surface O1 of the scanning element 60 at a right angle, they can pass without any diffraction. When scanning the one-dimensional arrangements of modulation elements 4 of the light modulator device 3, it is therefore important to ensure that two parallel surfaces of the scanning element 60, e.g. O1 and O2, are disposed at an angle to the optical path. It is of course not always necessary for the scanning element 60 to be tilted during the scanning process.
The projection elements 6, 7 and, perhaps, 8, which are disposed between the illumination device 1 and the scanning element 60, reshape the light beams 50, 51 and 52 such that they are focussed on the light modulator device 3. The scanning element 60 must be disposed in front of plane 11. If a transmissive light modulator device 3 is used, the scanning element 60 can be disposed either in front of or behind plane 11, or even in plane 11.
In the coherent direction, the modulated wave front WF, which is projected into plane 12, is subsequently projected in the projection system PS by the projection means 15 into a plane 16, in which a virtual image of the wave front WF is created according to this embodiment. This image of the wave front WF is then projected through the screen 14 into a virtual observer window 17, which does not exist physically, and which is located in an observer plane 18. At the same time, the Fourier transform FT of the modulated wave front WF, which is created in plane 11′ in the scanning system AS, is projected by the projection element 10 and projection means 15 on to the screen 14. In the non-coherent direction, the beams which are projected into plane 12 in a collimated manner are projected by the projection means 15 on to the screen 14. In addition, the scanning element 5, which is projected into plane 12, is projected by the projection means 15 and the screen 14 into the virtual observer window 17. This means that the observer window 17 is disposed in an image plane of a system which consists of the projection element 10, projection means 15 and screen 14 in the non-coherent direction.
It is advantageous if the screen 14 is disposed in the image-side focal plane of the projection means 15, because thereby the periodic continuation of the diffraction orders is displaced out of the screen 14, so that only one period of the diffraction spectrum is visible on the screen. This means that an observer does not perceive the periodic continuation of the reconstruction in the various diffraction orders. Further, it is advantageous if the light emitted by the light source 2 impinges areally on plane 12, whereby the observer window 17 and thus a reconstruction space 19 can be enlarged in the non-coherent direction. This means that the wider the wave front incident on plane 12 in the non-coherent direction, the larger is the observer window 17. It is thus advantageous if the focal length of the lens element 10b of the projection element 10 is greater than the focal length of the lens element 8b of the projection element 8, in order to enlarge the observer window 17.
The modulated wave fronts WF overlap in the observer window 17 one after another, and the Fourier transforms FT of the sequentially scanned one-dimensional arrangements of modulation elements 4 are projected to different positions on the screen 14. The wave fronts WF are thus sequentially projected to the observer window 17. An observer who is situated in the observer plane 18 and who looks through the virtual observer window 17 can see a reconstructed, preferably three-dimensional scene, which is reconstructed in front of, on or behind the screen 14, in a reconstruction space 19, which stretches as a frustum between the observer window 17 and the screen 14.
In this embodiment, the observer window 17 is at least as large as the eye separation of an observer. A second light modulator device 3 of the same type for a second observer eye and an corresponding adaptation of the entire projection device is thus not required. Alternatively, the observer window 17 may be smaller, but then at least a second scanning system AS must be provided for the second observer eye. If this is the case, the scanning systems AS can be arranged in parallel next to each other, or at an angle to each other. If the scanning systems AS are arranged in parallel, only one projection means 15 will be required for the two scanning systems AS. If the scanning systems AS are arranged at an angle, two projection means 15 are required for the two optical paths of two light channels.
Diffusing elements, such as diffuser foils or similar elements, may additionally be disposed in a plane which is projected on to the screen 14, in order to enlarge the observer window 17 in the non-coherent direction.
In order to be able to reconstruct the scene in colour, a beam splitter may be disposed between the plane 12 and the projection means 15, for example.
a is a top view that shows an enlarged detail of the projection system PS and illustrates how two light channels are simultaneously projected to serve a pair of eyes of an observer. The two light channels are arranged in parallel next to each other, and the modulated wave fronts of the two light channels are overlapped in a plane 62, which is the focal plane of the projection means 61, with the help of a single projection means 61 for the two light channels. This means that in front of the projection means 61, seen in the direction of light propagation, the modulated wave fronts are projected into infinite space. The screen 14 can for example be disposed in plane 62, otherwise this plane 62 must be projected on to the screen 14. If this device is used in conjunction with the projection device shown in
b also shows a detail of the projection system PS, and illustrates how two light channels are projected simultaneously. In contrast to the previous Figure, the light channels are not arranged in parallel, but at an angle. This is why there are two projection means 61, one for each light channel, to project the wave fronts into the plane 62.
c shows another detail of the projection system PS. The two light channels which serve a pair of eyes are arranged in parallel, as shown in
Other possibilities of beam passage through the projection system PS, which are similar to the options shown in
The projection means 23 and 15 can also be combined so to form one single lens or lens array. The above holographic projection device was only described for one observer eye; however, it can also be designed for a pair of observer eyes if the observer window 17 is large enough. Alternatively, a pair of observer eyes can also be served by a second light modulator device 3 for a second observer eye, then a number of modifications must be applied to the projection device. If the systems according to
Colour reconstruction of the three-dimensional scene is also possible with the help of the holographic projection device, as already noted above. For this, at least one beam splitter element 25, preferably a prism block, is disposed in front of the deflection means 21, seen in the direction of light propagation. Alternatively, the beam splitter element 25 may be disposed at any other suitable position in the projection device. Colour reconstruction of the scene is thereby achieved by simultaneously processing the three primary colours, RGB. If two fully separated light channels are provided, two beam splitter elements 25, i.e. one beam splitter element 25 per light channel, can be disposed in the projection system PS. The beam splitter element 25, which is preferably an X prism with dichroic layers, splits red, green and blue light into three separate wave fronts or recombines them to form a common modulated wave front. Colour reconstruction of the scene is achieved using three scanning systems AS per light channel, where each scanning system contains a monochromatic light source 2. The optical elements of the scanning systems AS can preferably be optimised such to be suited to the corresponding monochromatic light colour.
It is of course also possible to use a different optical element for colour reconstruction, such as the scanning element already mentioned above, which is in this case a scanning prism. Here, it is preferably designed to be of square or rectangular shape. This scanning prism for colour reconstruction is designed and functions as already described above. For colour reconstruction, the light beams 50, 51 and 52 emitted by three individual light sources 2 of the illumination device 1, or by one single light source 2 which exhibits sufficient coherence in each of the primary colours. The individual monochromatic waves are diverged with the help of a dichroic beam splitter system. The projection elements 6 and 7 can either be used commonly for the three primary colours, or they can be provided three times, so that each channel has separate projection means 6 and 7 for each primary colour.
Alternatively, sequential colour reconstruction of the scene is possible as well. To perform this type of reconstruction, a preferably coloured light source 2, which exhibits sufficient coherence, and a switching system are required in order to control the monochromatic primary colours, RBG, sequentially. This allows the colour reconstructions to be generated one after another. It is of course also possible when performing a monochromatic or sequential colour reconstruction of scenes to use only one scanning prism, and only one of the light beams 50, 51 or 52.
a and 9b show the scanning system AS in a simplified manner.
In the non-coherent direction, the projection elements 6 and 7 do not exhibit any optical effects, so that the beams emitted by the light source 2 impinge directly on the scanning element 5. The light source 2 in this embodiment is designed such that the emitted beams are sufficiently narrow in the non-coherent direction, so that it is not necessary for the projection elements 6 and 7 to have optical projection effects in that direction. The functional principle of the scanning system AS is explained below. Here, three linear arrangements of modulation elements 4 on the light modulator device 3 are scanned one after another, these three scans being represented by different lines in the Figure. The beams which are emitted by the light source 2 are directed on to the scanning element 5. Then, the beams pass the lens element 8b and the plane 11 and impinge on the light modulator device 3 at different positions, but with parallel optical axes, because the scanning element 5 is disposed in the focal plane of the lens element 8b of the projection means 8. The projection element 9 (=9′) does not contribute to the projection, because it is optically ineffective in the non-coherent direction. This is why the projection element 9 (=|10|) is not shown in
The holographic projection device described above was described for one observer eye only. However, it is possible to provide an observer window which is large enough for both observer eyes. Alternatively, it is possible to provide a second light modulator device 3 to serve a pair of observer eyes. The construction of such an arrangement with two scanning systems AS can be as already described above. If the observer is situated in the observer plane 18 (not shown) and looks through the observer window 17, he can see the reconstructed three-dimensional scene in the reconstruction space 19, where the scene is reconstructed in front of, on or behind the screen 14, seen in the direction of light propagation. Again, the position detection system 20 is provided in order to detect the position of the observer eyes and to track the observer window 17 accordingly. Further, it can now be seen clearly that the holographic projection device is simplified in the non-coherent direction, as the lens element 10c in plane 12 is omitted and the projection means 6 and 7 are designed much simpler. This construction further facilitates an alignment of the optical elements.
a and 11b show the functional principle of the holographic projection device again in a simplified, very compact form.
Referring to
Moreover, the projection element 6, which is disposed between the light source 2 and the projection element 7, or both projection elements 6 and 7, may be omitted, if the light source 2 is designed such that the emitted beams already conform with the required properties, e.g. as regards aperture width. In order to reconstruct a scene in colour, a beam splitter element can be disposed between the reflective light modulator device 3 and the projection element 9 (=9′), and three light modulator devices 3 are provided for simultaneous colour reconstruction. For sequential colour reconstruction, only one scanning system AS must be provided, because the light source 2 emits the required monochromatic wave fronts in the three primary colours one after another.
The holographic projection device further contains a beam splitter element 26, which is used in addition to the beam splitter element 25 which splits the light up into its spectral components or which recomposes the light from these components in a plane 27, to multiply the wave fronts WFR and WFL which are emitted by the light modulator devices 3. Plane 27 is the projection of plane 12 through the afocal system which consists of the projection means 29 and 30. Plane 12 can preferably coincide with the object-side focal plane of the projection means 29, and plane 27 can preferably coincide with the image-side focal plane of the projection means 29. At the same time, plane 27 coincides with the object-side focal plane of the projection means 22. The beam splitter element 26 is thus disposed in plane 27, and it can be a grid, prism or diffractive optical element (DOE), in particular a configurable DOE. Further, it is possible to provide multiple light sources 2 for each light modulator device 3, depending on. the number of observers in the observer plane 18, instead of the beam splitter element 26. The projection elements 6 and 7 must in this case be disposed such that the light emitted by the light sources 2 impinges on the light modulator device 3 at different angles of incidence.
In the coherent direction, the Fourier transforms FT of the two modulated wave fronts WFR and WFL are projected by the projection element 10 and the projection means 29 on to plane 28. Then, after multiplication of the Fourier transform FT by the beam splitter element 26 in plane 27 and deflection into another image plane of plane 28 by the deflection element 21, the multiplied Fourier transforms FT overlap on the screen 14. At the same time, the modulated wave fronts WFR and WFL, which are projected into plane 12, are projected into plane 27. After multiplication, the wave front WFR is simultaneously projected by the projection means 22, the three projection means 23 and the projection means 15 first into plane 16 and then into the observer plane 18 in the form of virtual observer windows 17R, 31R and 32R, on to the right eyes of the three observers. The wave front WFL is projected accordingly so to form virtual observer windows 17L, 31L and 32L for the left eyes of the three observers.
In the non-coherent direction, the scanning elements 5 of each scanning system AS are projected into plane 12. Then the scanning elements 5, multiplied by the beam splitter element 26, are projected into the observer windows 17R, 17L, 31R, 31L, 32R and 32L for the eyes of the three observers. At the same time, the beams are focused on to plane 28. Plane 28 in turn is projected on to the screen 14.
Each observer is only assigned one deflection element 21. The number of deflection elements 21 thus corresponds with the number of observers. This means that per observer only one deflection element 21 is used for both eyes, here for example for observer windows 17R and 17L. If an observer moves in the observer plane 18, the changed eye positions are again detected by the position detection system 20, and the deflection means 21 are controlled such that the observer windows 17R, 17L, 31R, 31L, 32R and 32L are tracked in accordance with the new eye positions of the observers. The three-dimensional scene can be reconstructed in colour as described above using the beam splitter element 25.
a and 14b show a second embodiment of a scanning system AS in the coherent and non-coherent direction, said embodiment being in contrast to
It is advantageous if diffractive optical elements are used as projection elements in the coherent direction, because their design and functional principle are better suited to achieve aberration correction. Now, the functional principle of the scanning system AS in the coherent direction is described. The light source 2 of the illumination device 1 emits sufficiently coherent light in the form of a wave W, which is directed on to the projection means 6 for broadening. The wave W then passes through the projection means 7 and is focussed on to the scanning element 5. This wave W is then focussed by the projection element 8 into plane 11, which is situated in the image-side focal plane of the projection element 8. After a preferable deflection of wave W by a deflection element, which can be a mirror and which is disposed in plane 11, this wave is projected by the projection element 9 preferably in the form of a plane wave front on to the light modulator device 3. The wave front WF modulated by the light modulator device 3 is then projected by the projection element 9′ (=9), into a plane 11′, which is situated in the image-side focal point of the projection element 9′ (=9). Because the light modulator device 3 is of a reflective type in this embodiment, planes 11 and 11′ coincide. At the same time, a Fourier transform FT is created in plane 11′.
It must be noted here again that the projection elements 9 and 9′ are represented by one single projection element, because the light modulator device 3 is of a reflective type, so that the modulated wave front WF is reflected back into plane 11 (=11′). Further, a preferable deflection element in plane 11 (=11′) is not necessarily required, so that it is possible to replace the projection elements 8 and 9 by a single projection element. If this is the case, the scanning element 5 will be disposed in the object-side focal plane of the projection elements 8 and 9.
In the non-coherent direction, shown in
Further, the projection element 7 may be disposed such that the first projection of beams in the non-coherent direction can be created virtually. Moreover, the projection elements 6 and/or 7, which is/are disposed between the light source 2 and the scanning element 5, may be omitted, if the light source 2 is designed such that the emitted beams already conform with the required properties, e.g. as regards aperture width. The scanning element 5 can of course also be a scanning prism, as described under
In a more compact version of the scanning system AS according to
The holographic projection device, in particular the projection system PS, again includes a position detection system 20 for detecting the eye positions of at least one observer in the observer plane 18 when viewing a reconstructed scene and for tracking the observer window 17 accordingly. The position detection system 20 can, for example, be a camera in conjunction with a deflection element 21 which is provided for tracking the virtual observer window 17 in the observer plane 18 in accordance with changes in the observer's eye positions. The deflection element 21 is in that case disposed between the two projection means 22 and 23. The projection means 22 and 23 represent an afocal system, where the deflection element 21 is disposed in the image-side focal point of the projection means 22, which is at the same time the object-side focal point of the projection means 23. The deflection element 21 can be discretely controlled and is preferably a mirror element, as described under
The thus reconstructed scene can be observed in a frustum-shaped reconstruction space 19 (not shown), which stretches between the observer window 17 and the projection means 15. The virtual observer window 17 can be as large as the eye separation of an observer, but it may also be smaller or larger. If the observer window 17 is smaller than an eye separation, two light modulator devices 3 are required, so that the scene can be watched with both eyes.
It is again possible in this embodiment to dispose the beam splitter element 25 in the projection device, for example at a suitable position between the plane 11′ and the projection means 22 in front of the deflection element 21, in order to be able to reconstruct the scenes in colour. Of course, other positions in the projection device are possible as well, as indicated for this embodiment in the Figure. Here, the beam splitter element 25 is disposed between the three light modulator devices 3 for the three primary colours and the projection element 9 (=9′). This embodiment thus allows simultaneous colour reconstruction of a three-dimensional scene. It is of course also possible to holographically reconstruct the colour three-dimensional scene sequentially, e.g. using only one light modulator device 3.
Of course, it is possible to depart from the embodiments shown above without leaving the scope of the invention.
Possible applications of the holographic projection device include displays for a two- and/or three-dimensional presentation in private or working environments, for example computer displays, mobile phone displays, TV screens, electronic games, in the automotive industry for displaying information, in the entertainment industry, in medical engineering and in military engineering for the representation of surface profiles. It appears to those skilled in the art that the present projection device can also be applied in other areas not mentioned above.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102006024356.0 | May 2006 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2007/054781 | 5/16/2007 | WO | 00 | 10/6/2009 |
