DE102011005154B4 - Light modulation device for a holographic or an autostereoscopic display - Google Patents

Abstract

Light modulation device for a holographic or an autostereoscopic display for displaying three-dimensional image information with at least one real or virtual light source (100), at least one light modulator (400) for encoding the image information to be displayed for at least one viewer eye (1100) of at least one viewer, a first light influencing means ( 500) and a second light influencing means (600), different from the first light influencing means (500), for changing the light path of the light emitted by the light source (100), an eye position detection system (800) for detecting and tracking at least one eye position of the at least one viewer of the image information and one System controller (900) for tracking at least one visibility region (1000) of the image information using the eye position data (901) supplied by the eye position detection system with the aid of the first and the second light element Influencing means (500, 600), characterized in that the first light influencing means (500) has a switchable polarization-influencing element (591) and a polarization grating (593), that in the direction of light propagation the switchable polarization-influencing element (591) is arranged in front of the polarization grating (593), that the polarization grating (593) according to the polarization direction of the incident light and depending on the position of the switchable polarization-influencing element (591) the light either in a +1. or into a -1. Diffraction order diffracts that with the first light influencing means (500) the visibility range (1000) within an observer range can be tracked to the eyes of the observer in rough steps, and that the second light influencing means (600) the visibility range (1000) at least in the range of a rough step of the first Light influencing means (500) finely graded or continuously tracks the eyes of the viewer (1100) with the aid of at least one electrically controllable diffraction grating.

Description

The invention relates to a combined light modulation device for a holographic or an autostereoscopic display with user tracking.

A combined light modulation device within the meaning of this invention is understood to be a device that changes the properties and/or the direction of light emanating from one or more real or virtual light sources in a multi-stage process.

A virtual light source is a light source that appears to be in one place, which appears as a result of the light from a real light source being influenced by generally static imaging means, for example a mirror, and/or beam-limiting means, for example screens.

A holographic display within the meaning of this application is a display device for three-dimensional image data in which the three-dimensional object data of the scene to be displayed are written as a diffraction pattern of the scene to be reconstructed. Both a large computational effort and a high-resolution light modulator are required for the reconstruction of a three-dimensional scene in a large visibility range with high quality.

The applicant has therefore in the patent DE 103 53 439 B4 proposed a method in which the wavefront is calculated for only a small visibility range, the diameter of which is only slightly larger than the diameter of a pupil of an observer's eye. As a result, the object points to be reconstructed only need to be encoded in respective sub-holograms in a small area of the light modulator.

For this purpose, at least one light modulator is illuminated with sufficiently coherent light from at least one light source and this light is imaged onto at least one viewer eye by means of a field lens. The reconstruction of the three-dimensional scene for the second observer eye can be generated by encoding an associated hologram or the associated sub-holograms in the light modulator by switching on at least one further light source in alternation and synchronized with the light modulator. A colored representation is possible by spatially or temporally interleaving (multiplexing) the hologram information for the individual color components. So that the viewer can move freely in front of the display, the focus areas are tracked to the viewer's eyes by switching on additional light sources separately. For this purpose, the eye coordinates of one or more viewers are constantly determined with the aid of a position detection system.

By recalculating the diffraction pattern, the reconstruction of the scene can be adapted to the new viewer location. By nesting them in time, reconstructions can also be displayed for several viewers.

For user tracking along the light path, it is also advantageous to adapt the focal plane of the focusing unit and thus the size of the visibility region to the eye position of the viewer.

In an autostereoscopic display (ASD) with user tracking, no diffraction patterns are encoded in the light modulator, but the scene views for the respective eye are written directly.

The user tracking can take place, for example, by direct or indirect displacement of the light sources. A well-known example of indirect shifting are deflection mirrors.

Numerous other methods of user tracking are known. This can be done by changing the light path in front of or behind the light modulator used for hologram coding or stereo imaging. In addition to mechanical methods, methods are known for changing reflecting, diffractive or refractive properties using adaptive optics.

Combined tracking variants are also known, which have a fixed light deflection function that varies over the surface of the light deflection means.

In the applicant's patent application DE 10 2008 054 438 A1 a matrix of electrically controllable liquid cells is proposed for user tracking, the liquid cells having additional light deflection means which are fixed but vary over the surface of the matrix, in order to implement or support a field lens function, for example. These light deflection means can have, for example, refractive elements such as prisms or lenses, or diffractive elements such as volume gratings or blazed gratings, ie gratings that are optimized for an intended wavelength.

the EP 2 160 658 B1 discloses a holographic reconstruction system in which the tracking of an observer window to the current eye position of an observer by means of an electro-optical deflection means with at least one deflection means field with adjustable microcells, which has regularly structured electro-wetting cells with discretely adjustable light deflection. In the DE 10 2007 051 521 A1 a cell array is also described, with which the light intensity can be directed into different orders of diffraction.

the U.S. 4,627,039 A and U.S. 3,872,348 A each describe that coarse- and fine-stepped alignments of light and electron beams are customary in the art in optical storage devices and in CRT tubes.

the DE 10 2007 019 277 A1 discloses a holographic reconstruction device in which the light modulator is associated with a filter diaphragm array.

the DE 602 12 398 T2 discloses a birefringent lens array with a switchable polarizer.

In the applicant's patent application DE 10 2009 028 626 A1 , the disclosures of which are incorporated herein by reference, teaches using controllable diffractive gratings for user tracking.

In order to achieve a larger deflection angle, these gratings can also be arranged one behind the other with the same deflection direction. For two-dimensional deflection, it is also possible to connect at least two controllable deflection gratings rotated relative to one another by a fixed angle. By varying the inscribed grating period over the surface of the deflection unit, the diffractive gratings can realize a locally different deflection in order to achieve or support a field lens function.

For a controllable deflection grating whose grating period can be changed in order to set a desired diffraction angle, there is a minimum adjustable period due to the spatial resolution with which the deflection grating can be controlled. If, for example, the period is set by means of a grid-shaped electrode structure, the width and distance of the electrodes are limited due to production. In addition, crosstalk between set adjacent phase values occurs, for example due to electrical stray fields or scattering or diffracting components of the deflection grid. These can also lead to a reduction in the diffraction efficiency and thus to interfering scattered light or to light in higher diffraction orders.

Since the diffraction angle is inversely proportional to the periodicity of the diffraction structure for a diffraction structure designed in the form of a grid, the controllable angular range and thus the tracking range for a single diffraction device is limited by the electrode spacing that can be produced.

For comfortable viewing of a 3D scene from different perspectives, however, a display with a large tracking range and a variable viewing distance is required. A solution is sought which, despite the limitation of the deflection angle of a deflection element, allows a tracking range which is larger than the deflection angle that can be achieved with this element.

According to the invention, the object is achieved with the features of claim 1.

A light modulator device for a holographic or an autostereoscopic display for displaying three-dimensional image information with at least one real or virtual light source, at least one light modulator for encoding the image information to be displayed for at least one viewer eye of at least one viewer, a first and a second light influencing means for changing the light path of the light emitted by the light source, an eye position detection system for detecting and tracking at least one eye position of the at least one viewer of the image information and a system controller for tracking at least one visibility region of the image information using the eye position data supplied by the eye position detection system with the aid of the first and second light influencing means , which defines the visibility range within a viewer range eyes of the viewer in rough steps and by a second light influencing means, which finely graded or continuously tracks the visibility range at least in the area of a rough step of the first light influencing means of the eyes of the viewer with the help of at least one electrically controllable diffraction grating.

The system controller selects that deflection direction of the first light influencing means that comes closest to the currently selected eye position of the selected viewer and sets this in the first light influencing means. The difference angle between this deflection angle and the actually selected eye position is calculated simultaneously or promptly by the system controller and set in the second light influencing means.

Both eyes of a selected viewer can be served by the system controller in time-division multiplex mode, with the eye position detection system supplying the necessary eye position data.

For a 3D display, the image content to be displayed, i. H. the respective stereo view or the encoded hologram, adapted to the respective right or left eye. The eye recognition system can also be configured as a system for recognizing the viewing direction, e.g. in a system with a large possible viewing angle, to reconstruct only the parts of a scene that the viewer is looking at.

Several viewers can also be operated in time-division multiplex mode, which, however, requires fast light modulators and fast light influencing means.

For a flicker-free display, a refresh rate of at least 60 frames per second is required for each view of the time-division multiplex operation. With simultaneous time-division multiplexing of the three color components and the two eyes of each viewer, this value relates to the view of a color channel for one eye of a viewer.

Especially in the case of a projection system, it is possible to use a separate deflection system for each observer eye, which allows simultaneous display of the image content for both observer eyes via a beam combination system.

By adapting the image content to be displayed by the system control to the respective viewer position, it is possible for the viewer to move around the image content to be displayed when moving his head within the visibility area of the display, whereby this effect can also be artificially exaggerated or reduced.

Since achromatic diffractive steel deflection systems can only be produced with a great deal of effort, in a preferred embodiment variant, color representation also takes place in time-division multiplex operation of the individual color components.

Depending on the design of the light modulation device, the second light influencing means with the controllable light deflection grids can be located in front of or behind the first light influencing means for coarse light deflection. A light influencing means for coarse light deflection, which requires fixed entry angles for its function, as z. B. represent volume grating for diffractive beam deflection is arranged in an advantageous manner in front of the second light influencing means.

One or both light influencing means can be arranged in front of or behind the light modulator.

They can be designed for a transmissive, an emissive or a reflective light modulator.

A transmissive or reflective light modulator is used in connection with an illumination device, which usually generates collimated light with which the light modulator is illuminated.

Examples of transmissive modulators are liquid crystal modulators on a transparent substrate with a multiplicity of controllable liquid crystal cells arranged in rows and columns, or modulators based on electrowetting cells.

Examples of suitable reflective modulators are liquid crystal modulators on a reflective substrate (e.g. LCOS—Liquid Crystal on Silicon) or micromirror arrangements (DMD—Digital Micromirror Device) as fast light modulators.

In the case of a transmissive or reflective light modulator, the first and/or the second light influencing means or parts thereof can be integrated into the lighting device.

If, for example, the light modulator is a phase modulator for encoding complex hologram values in two (two-phase coding) or more phase pixels of the modulator, in which the phase values that belong together are then combined in beam combination optics to form an intensity value with a defined amplitude and phase value, that’s it advantageous to arrange both light influencing means behind the light modulator when the beam combining optics requires a defined transmission direction.

Such a beam combining optics is, for example, in the not yet published German patent application DE 10 2009 044 910.8 suggested.

However, it can be advantageous in the case of an autostereoscopic display with an amplitude modulator that is largely direction-independent or a holographic display with a complex-valued modulator that is largely direction-independent be able to partially or fully integrate one or both light influencing means into the lighting device of the light modulator.

Remaining direction-dependent intensity dependencies can advantageously be taken into account by the system controller when encoding the image information, so that these dependencies can be compensated for.

Emissive light modulators, such as electroluminescence displays or plasma displays, do not require a lighting device since they themselves serve as a light source. Since their individual pixels are incoherent with one another, they are preferably used as light modulators in autostereoscopic displays.

In holographic displays, their use as a switchable light source can be used in combination with collimation optics of the lighting device of a transmissive display if the extent of a pixel is small enough to have a sufficient coherence length.

The beam directions of the light sources are selected by the two light influencing means with the aid of the system control in such a way that the information to be displayed for the moment is in the visibility range of an observer's eye.

Depending on the design and the type of coding, the light path can only be changed in the horizontal direction or in the horizontal and vertical direction.

Tracking the visibility range only in the horizontal direction greatly simplifies the structure, since only light influencing means are required that can change the light path in one direction.

In the case of a holographic display, the computing effort for the hologram calculation is considerably reduced in the case of a one-dimensional coding compared to a two-dimensional coding.

In the case of one-dimensional observation, real or virtual light sources can be used. These could be, for example, display columns of an emissive display with upstream collimation optics in the form of cylindrical lens arrays. In the case of autostereoscopic displays, only a horizontal viewing direction is often implemented.

By changing the position of a real or virtual light source in front of a collimating optics in horizontal or vertical direction, the direction of the collimated illumination beam can be changed in horizontal or vertical direction. This can be realized, for example, by switching on or controlling the brightness of individual light points or light point areas of a high-resolution light source matrix in connection with an upstream field of collimation optics, for example a lens array.

Illumination strips can be used in conjunction with a cylindrical lens array for one-dimensional deflection.

A deflection of the points of light or strips of light can also be realized mechanically or by scanning (scanning) methods.

By shifting the light sources in the direction of the optical axis of the associated collimation optics, the size of the light spot in the viewing plane can be adjusted. This can also be achieved by collimation optics whose refractive power is variable and can be controlled accordingly.

A light influencing means, which has a light source array with displaceable light sources and associated collimation optics, can also serve as part of the lighting device when using a transmissive modulator.

By controlling the brightness of individual light source points, errors in the optical system can be compensated for.

If individual points of light in the controllable light source matrix are at a clear distance from one another, the visibility range can be tracked in rough steps. The average deflection angle α for a light source which is at a distance I from the main plane on the object side and at a distance a from the optical axis of the collimation optics is: $$\mathrm{a}=\text{arctan}\left(\text{a}/\text{I}\right)$$

For example, the center beam of a light source that is 10mm in front of the object-side main plane of the collimating optics and has a lateral offset of 2mm compared to its optical axis has a beam inclination of 11.3 degrees compared to the optical axis.

As already shown, a light influencing means can be made up of several individual components. The first and / or the second light influencing means of the light modulation device can be composed of several light influencing elements, with which independently of each other the beam direction and / or Position of the real or virtual light sources can be changed.

Several electrically controllable deflection gratings with the same deflection direction can be partially or completely connected in a row in order to increase the achievable deflection angle or to realize a separate deflection area. For a two-dimensional deflection, one-dimensional deflecting light influencing elements can be combined to form a light influencing means. This can be done, for example, in a crossed arrangement.

The individual light influencing elements of a light influencing means can also be based on different physical principles of action.

The system control takes into account the deflection properties of each individual element, and it is possible to compensate for errors that arise in one element in one or more other elements.

By changing the size of the change in position of the light from the light source and/or the size of the change in beam direction in the first and/or in the second light influencing means depending on the point at which the light hits the surface of the light influencing means, a field lens function can be implemented to define the size of the visibility area in the viewer plane or affect the effect of a separate field lens.

By controlling this change in position or beam direction over the surface of one or more light influencing means by the system controller, the size of the visibility area can be variably changed and thus, for example, this size can be adapted to a changed observer distance from the display, so that the visibility area remains larger than the pupil diameter is smaller than the interpupillary distance.

To do this, the system controller evaluates the position or distance data supplied by the eye detection system and adjusts the calculated angle changes in the associated light influencing means in addition to the lateral angles that define the position of the visibility area in the observer plane.

The beam direction change in the light influencing means for the rough tracking of the visibility range can contain both diffractive and refractive light influencing elements.

In a design variant with a fixed light source matrix, the individual lenses of the collimating optics have a controllable lens effect, so that the focal length and/or the lateral location of the lens apex can be changed. Such a controllable lens based on an electrowetting cell is described in the European patent, for example EP 1579249 B1 described.

Volume gratings into which at least two holograms are inscribed can advantageously be used in the first light influencing means for a roughly graded beam deflection.

The required volume grid or a template for further copies can be produced by exposing the holograms with the desired entry and exit distributions with the respective working wavelength. The holograms can also be exposed in an optical system which essentially corresponds to the application system or is contained in it (in-situ exposure) in order to compensate as completely as possible for image errors of the optical components involved.

Volume gratings can be optimized for very narrow entrance angles that differ only slightly from one another and/or for narrow wavelength ranges. In this way, high diffraction efficiencies of approximately 100% can be achieved for phase holograms. The volume gratings act as an angle filter, i.e. only light from a narrow angle range is diffracted in the desired direction, and/or as a wavelength filter, with only light from a selected wavelength range being diffracted in the desired direction. Light of other angles or wavelengths passes through the volume grating without being diffracted.

So that only one diffraction order occurs when light passes through the volume grating, i.e. for example the first, second or a higher diffraction order, the Bragg condition must be observed and the refractive index modulation selected accordingly. If the refractive index modulation deviates from the optimum, an undiffracted portion of the light, i.e. a zero diffraction order, is present - even if the Bragg condition is observed.

Depending on the thickness of the volume grating and the maximum possible difference in refractive index, it may be necessary to illuminate the grating in such a way that multi-beam interference occurs, ie the individual light rays pass through a sufficient number of grating planes. This means that the minimum diffraction angle generated is not too small, for example 30 degrees. This can be achieved by obliquely illuminating the volume grid. A necessary pre-deflection can be generated by an additional upstream volume grid if the geometric conditions require it.

The thicker the volume grating is, the greater its selective effect.

größer 10 ist. Dabei ist d die Dicke des Volumengitters, λ die Arbeitswellenlänge des Lichtes im Vakuum, A die Gitterkonstante des Volumengitters und n₀ die mittlere Brechkraft.The diffraction processes at volume lattices were described by Kogelnik using the theory of coupled waves (H. Kogelnik, "Coupled Wave Theory for Thick Hologram Gratings", Bell Syst Techn. J. 48 (1969) 2909-2947). Thick is a volume lattice if its Q factor $$\text{Q}=2\mathrm{\pi }\text{i.e}\mathrm{\lambda }/\left({\text{n}}_0{\mathrm{\Lambda }}^2\right)$$

is greater than 10. Here d is the thickness of the volume grating, λ is the working wavelength of the light in a vacuum, A is the grating constant of the volume grating and n ₀ is the mean refractive power.

Instead of a volume grating that is optimized for several entry angles and/or several wavelengths, several volume gratings with a smaller range of functions can be connected in series, i.e. each volume grating deflects the light in a different direction or focuses it at a different location.

In addition to different exit angles, additional field lens functions can advantageously be exposed into the volume grating during production, which delimit the diameter of the visibility region in the observer plane.

In general, any number of different wave fields can be reconstructed using angle multiplex. This corresponds to the principle of holographic reconstruction. In this way, field lenses with different focal lengths can also be reconstructed. It can also be advantageous to reconstruct plane waves propagating in different directions, e.g. B. a separate field lens is present.

The foci of the field lenses, which are generated by light distributions with different entrance angles, do not have to lie in the same plane as these. For example, a series of field lenses could also be generated from light distributions with different vertical entrance angles, the foci of which differ e.g. in the horizontal direction, in the horizontal and vertical direction or in the horizontal direction, in the vertical direction and in the focal plane.

In order to generate or support a field lens function, it is possible to split the volume hologram into at least two partial holograms arranged next to one another, each of which satisfies the Bragg condition with a slightly different exit angle, ie the volume grating is segmented. The production and mode of operation of such volume holograms is - seen per se - for example from the German patents DE 19 700 162 B4 or DE 19 704 740 B4 famous.

To select the individual directions written into the volume hologram, at least one horizontal and/or vertical displacement unit can be present, which influences the light from the light sources in a controllable manner such that the angle of incidence and/or the point of incidence on the volume hologram can be changed. In this case, this unit can, for example, be part of a background lighting device in the case of a transparent light modulator or a front lighting device in the case of a reflective light modulator. The necessary shifting and/or tilting is set by the system control based on the determined selected eye position. It can be done in a known manner using mechanical, reflective, refractive or diffractive methods. When using a flat lighting device, for example, the coupling angle can be varied in a planar waveguide.

A further advantageous embodiment variant uses several narrow-band light sources for each wavelength range, e.g. for the red, the green or the blue spectral range, which differ only slightly in their focal point wavelength and which are selectively selected and activated by the system control in order to convert the individual diffraction angles into to select or address the at least one volume grid. Lasers, for example semiconductor lasers, or narrow-band light-emitting diodes can preferably be used for such light sources.

Depending on the selected narrow-band spectral ranges, the system controller can carry out a color correction of the information to be displayed.

Both methods can be combined with one another, so that diffraction gratings for different angles of incidence and for different, closely adjacent wavelengths are written into the at least one volume hologram.

In a further embodiment, at least one polarizer, which can be switched by the system controller, is used in connection with at least one birefringent lens in the first light influencing means for coarsely graded changes in the beam direction. Such a system is, for example, from WO 03 015 424 A2 for the 2D/3D Known switching in an autostereoscopic display.

A birefringent material, for example a liquid crystal mixture, is arranged between two interfaces of two transparent media, which serve as the substrate. At least one boundary surface is partially curved in order to achieve a lens effect and/or partially inclined in relation to the other in order to achieve a wedge effect.

By selecting one of two possible directions of polarization using the switchable polarizer, one of two possible lens and/or deflection effects can be selected with the aid of the system control. The strength of the lens power and/or the wedge angle can vary over the surface of the deflection and/or focussing unit. It is also possible to design the switchable polarizer in a segmented manner in order to select the two directions of polarization in a locally variable manner.

The switchable polarizer can be formed, for example, as a variable delay plate using an electrically controllable birefringent material, which can also consist of a liquid crystal mixture, for example. The birefringent material is embedded between two substrates that are provided with suitable electrode structures. Here, too, it is possible to connect several such light influencing elements in series in order to increase the overall effect in the light influencing means.

Instead of a switchable polarizer and a fixed birefringent light influencing element, switchable birefringent light influencing elements can also be used. In such a device, as z. B. for 2D / 3D switching in autostereoscopic displays in the WO 2007/007 285 A2 is proposed, the number of substrates required can be reduced compared to the aforementioned solution. These light influencing elements can also be segmented and/or arranged one behind the other.

Suitable electrode structures can also be used to produce planar light influencing elements in which, by applying suitable electric field distributions, a controllable gradient index profile of the refractive index can be generated, with which the light direction can be influenced.

In further configuration variants, at least one polarization grating is used to influence the light. In such a lattice only the -1 exist. the 0th and the +1. diffraction order. By using incident circularly polarized light, it is possible to direct almost 100% of the light, depending on the direction of rotation of the circular polarization, only into the +1. or only in the -1. deflect diffraction order.

Both actively switchable polarization gratings and passive polarization gratings are known. Polarization gratings can be produced by aligning liquid crystals on appropriately prepared surfaces. Such surfaces, which act as structured alignment layers (alignment layer) for the liquid crystals, can be produced, for example, by polymerizing linearly photopolymerizable polymers (LPP—linearly photopolymerizable polymer). For this purpose, the layers are, for example, provided with interference patterns of circularly polarized ultraviolet light, e.g. B. from a UV laser, formed accordingly.

With little or no voltage on an electrode structure, the active polarization gratings form a periodic grating structure and, depending on the direction of rotation of the incident circularly polarized light, can be converted into the +1. or in the -1. Deflect diffraction order with high diffraction efficiency. With a sufficiently high voltage, the liquid crystals can be aligned in such a way that the lattice structure is destroyed, so that the incident light in the 0th diffraction order passes undeflected through such a light influencing element.

Passive gratings can be formed, for example, by polymerizing liquid-crystal polymers (LCP). Both active and passive polarization gratings can be used in combination with a switchable polarizer, such as a switchable retarder plate, to select the desired diffraction order. With an active polarizing grating, the system controller controls both the switchable polarizer and the controllable grating to select the desired diffraction direction. In the case of a passive grating, only the switchable polarizer is controlled for this purpose. It is possible to connect several combinations of switchable polarizers and polarization gratings in series as light influencing elements. The grating constant of the polarization grating can be varied over the light entry surface in order to achieve a locally different deflection effect. This variation can be continuous or segmented. This can e.g. B. a field lens function can be implemented or supported. For example, cylindrical lenses or crossed cylindrical lenses can also be implemented.

In order to select the appropriate diffraction angle by the system control, the areal switchable polarizer can also be structured.

If the grating is used in combination with other light deflection elements, for example an attached field lens and/or other light influencing elements, the grating must be optimized locally for a correspondingly slanted incidence of light. In the case of an active polarization grating, this can be done by locally adapting the control voltage and thus the effective birefringence.

In the case of passive polarization gratings, the hologram used for production must have a local variation in the grating period.

With a simple polarization grating, the deflection angle depends on the wavelength. In a color display, in which the individual color components are generated in a time-division multiplex operation, this angular difference must be compensated by the system controller in further controllable deflection elements.

From the WO 2008/130 561 A1 are e.g. B. also multi-layer systems of passive polarization gratings are known, in which the deflection angle remains almost constant over a wide spectral range.

In a further embodiment variant, diffractive gratings are used for coarse light deflection, the grating period of which can be changed by changing the voltage applied to a liquid crystal cell. Such a system is, for example, in U.S. 6,188,462 B1 described. By varying the voltage applied across the grid surface, a locally different deflection angle can also be variably set here by the system controller.

Advantageously, diffractive phase gratings can also be used for coarse light deflection, such as are provided for continuous deflection in the second light influencing means. With these gratings, the grating periods and thus the size of the deflection angle are set by applying a sawtooth-shaped voltage gradient to a fine electrode structure. The smallest possible grid period and thus the largest possible deflection angle is determined by the electrode grid. Since very fine grids with a grid period of a few micrometers to a few hundred nanometers are difficult to control, especially with large-area deflection grids, electrodes for the deflection grid can be combined for coarse deflection and a common signal can be applied if their distance is greater than the grid period for the largest possible deflection angle for the deflection grating for the finely graded deflection. For example, the deflection grid for fine-scale deflection can have an electrode period of a few micrometers, with which each electrode can be controlled individually, and the deflection grid for coarse-scale deflection can consist of a grid with an electrode spacing of less than one micrometer, in which electrodes can be are combined over a greater distance than corresponds to the electrode grid of the fine-stepped grid.

The combination of the electrodes can be segmented over the area of the deflection grid. It is also possible to vary the electrode grid over the grid area, e.g. B. at the edge of the grid by a finer electrode grid to allow a larger deflection angle required there.

For beam deflection of light beams with a small cross-section, such as are emitted in the lighting device from light sources with a small extent directly or after appropriate beam shaping, further light deflection elements can advantageously be used in a transmissive or reflective mode of operation. For example, acousto-optical modulators (AOM) allow high-speed beam deflection. The deflection angle can be changed by varying the control frequency. The diffraction efficiency can be influenced by the level of the control voltage. There are also known AOMs that have multiple sound transducers that can be controlled with phase-shifted signals. As a result, the effective phase grating in the AOM can be tilted depending on the phase position and thus adapted to changing exit angles, so that the Bragg condition is largely fulfilled with the same entrance angle, in order to obtain high diffraction efficiency for a wide output angle range and a wide working wavelength range. Such a modulator is, for example, from U.S. 5,576,880 famous. Since only small deflection angles can be generated with an AOM, a volume grating with several encoded exit angles or a corresponding volume grating stack of individual gratings, each with different exit angles with entrance angles that differ only slightly, can be connected downstream to increase the angular range. Such an arrangement is, for example, from U.S. 3,980,389 famous.

All optical boundary surfaces of the light influencing means or light influencing elements should advantageously be provided with antireflection layers to avoid scattered light. These can be used in a known manner depending on the application tion can be carried out spectrally and/or angularly in a narrow or broadband manner.

Suitable diaphragms for filtering out unnecessary orders of diffraction and/or scattered light can be contained in the optical beam path. The use of additional means for wavefront shaping, such as apodization masks, is also possible.

Other possible measures for optimizing and special design of the method, such as the use of lookup tables for quick calculation of the setting parameters for the deflection angle, the use of common substrates in the multilayer structure of light deflection elements, measures for calibration, for error compensation, for compensation of a temperature influence, for Compensation for aging phenomena or for designing the control circuits and electrode structures are part of this invention and are not explained in more detail since these measures are known to a person skilled in the art with knowledge of the teaching according to the invention described here. All controllable components can also be designed as controllable components with the help of suitable additional measuring devices.

Instead of electrically controllable diffraction gratings, other known light deflection elements can also be used for continuous observation.

• 1 eine erste Ausgestaltungsvariante der Erfindung,
• 2 einen Ausschnitt aus einem Lichtbeeinflussungsmittel zur grob abgestuften Nachführung mittels schaltbarer Lichtquellen,
• 3 ein Lichtbeeinflussungsmittel zur grob abgestuften Nachführung mittels schaltbarer Lichtquellen mit zusätzlicher Feldlinsenfunktion,
• 4 einen Ausschnitt aus einem Lichtbeeinflussungsmittel zur grob abgestuften Nachführung mit einem Lichtquellentracking mittels diffraktiver Ablenkgitter in der Beleuchtungsvorrichtung,
• 5 einen Ausschnitt einer Beleuchtungsvorrichtung mit einem Volumengitter und Winkelmultiplex
• 6 eine Lichtmodulationsvorrichtung mit einem reflektiven Modulator,
• 7 die Erzeugung zweier Feldlinsen mit Hilfe eines aktiven Flüssigkristallgitters,
• 8 eine Lichtmodulationsvorrichtung mit einem transmissiven Modulator und einem Flüssigkristallphasengitter mit steuerbarer Gitterperiode in Verbindung mit einer Multiplexfeldlinse,
• 9 eine flache Hintergrundbeleuchtungsvorrichtung, welche eine vertikale und eine horizontale Verschiebung des durch eine Kollimationseinheit erzeugten Wettenfetdes vor dem Eintritt in ein erstes Volumengitter ermöglicht,
• 10a bis 10c die beispielhafte Wirkungen zweier steuerbarer Volumengitter als vertikale Lichtbeeinflussungselemente aus der 9 und
• 11 eine Lichtmodulationsvorrichtung mit einem transmissiven Modulator und einem Polarisationsgitter in Verbindung mit einem schaltbaren Polarisator.

There are now various possibilities for embodying and developing the teaching of the present invention in an advantageous manner. For this purpose, on the one hand, reference is made to the patent claims subordinate to claim 1 and, on the other hand, to the following explanation of the preferred exemplary embodiments of the invention with reference to the drawings. In the drawings show (each in a schematic representation)

• 1 a first embodiment of the invention,
• 2 a section of a light influencing means for roughly graduated tracking using switchable light sources,
• 3 a light influencing device for roughly graded tracking using switchable light sources with additional field lens function,
• 4 a section of a light influencing means for roughly graded tracking with light source tracking using diffractive deflection gratings in the lighting device,
• 5 a section of a lighting device with a volume grating and angle multiplex
• 6 a light modulation device with a reflective modulator,
• 7 the creation of two field lenses using an active liquid crystal lattice,
• 8th a light modulation device with a transmissive modulator and a liquid crystal phase grating with controllable grating period in connection with a multiplex field lens,
• 9 a flat backlight device which allows vertical and horizontal displacement of the bet fat generated by a collimation unit before entering a first volume grating,
• 10a until 10c the exemplary effects of two controllable volume grids as vertical light influencing elements from 9 and
• 11 a light modulation device with a transmissive modulator and a polarization grating in connection with a switchable polarizer.

In 1 a typical design variant of a light modulation device is shown schematically. A light source 100, which is embodied here as a planar light source field, includes a large number of individual light sources 101 to 123 with a small extent, which can be switched individually or in groups via a system controller 900 or whose brightness can be controlled or regulated. In this case, each individual light source 101 to 123 can also consist of a plurality of light sources with different focal point wavelengths, which can also be controlled separately. The light sources 101 to 123 illuminate a planar light modulator 400 via collimating optics 200, which can consist of a field of individual lenses 201-203 or strips of cylindrical lenses. The lenses 201 to 203 can also be designed to be controllable, so that their focal point can be or three directions by the system controller 900 can be variably adjusted. This is particularly important when the device is designed for multiple viewers 1 In the example shown, a transmissive light modulator 400 is used, which changes the amplitude and/or the phase of the light over an area. The controllable light source field 100 in combination with the collimation optics 200 forms a dynamic lighting device 300.

The light modulator 400 receives its modulation values for the display of three-dimensional image information from the system controller 900, which determines these values based on the input data of the 3D scene 902 and the position data of at least one eye position 1100 of at least one viewer of the image information supplied by an eye position detection system 800. The system controller 900 takes into account the characteristic curve of the light modulator 400 and other correction values that result from the design of the optical system and the position data. The image information to be displayed, in particular the scene section to be displayed, can also be processed outside of the system controller 900 using the eye position data 901 supplied by the system controller 900 to an external computing unit. The eye position detection system 800, which is known per se, can e.g. B. consist of at least one camera and an associated evaluation unit, wherein the evaluation unit can also be part of the system controller 900. The evaluation unit determines the position of the eye pupils in the respective camera image from the camera images and calculates the associated location coordinates of all observer eyes 1100 from this , can be used.

In the light path between the light sources 101 to 123 and the observer's eyes 1100 there can be further light influencing elements 501 which are controlled by the system controller 900 . In the exemplary embodiment shown, the dynamic lighting device 300 forms the light influencing means 500 for the coarse beam deflection, alone or in combination with the further light influencing elements 501 . A second light influencing means 600 in the form of diffractive, controllable deflection gratings is provided, which can also be composed of several light influencing elements, so that the respective visibility region 1000 can be continuously or finely gradated directed to the respective observer eye by the system controller 900 using the eye position data 901. For focusing the visibility area 1000 on the observer plane, the example shows 1 a field lens 700 is present, which can also be designed as a controllable adaptive lens, which enables the expansion of the visibility region 1000 to be adapted to the distance between the observer's eyes 1100 and the light modulator 400 via the system controller 900 . However, the function of the field lens 700 can also be partially or fully integrated into the dynamic lighting device 300 and/or into further light influencing elements 501 and/or into light influencing elements of the second light influencing means 600 .

2 shows schematically a section of an illumination device, which is designed as a light influencing means for the roughly graded tracking of at least one visibility region to the location of at least one observer's eye by means of switchable light sources 101 to 103.

A large number of switchable or controllable light sources 101, 102, 103 are located in front of collimation optics 200, which can contain refractive and/or diffractive elements. The desired direction of deflection is selected by switching on one of the light sources 101, 102 or 103 shown as an example. The deflection angle depends on the distance of the light source from the optical axis OA of the segment of the collimating optics 200 and its distance from the object-side main plane of these imaging segments. In the example shown, the light sources 101 to 103 are located in the focal plane on the object side, so that the collimation optics 200 emit parallel light. This illuminates the light modulator 400.

3 shows a variant of the roughly graded tracking by means of switchable or controllable light sources 101-123 with an additional field lens function. The individual light sources 101 - 123 of a light source 100, which is designed as a planar light source field, are arranged asymmetrically behind the collimating lenses 201 - 203 of a collimating optics 200, so that the light from the light sources 101 - 123, which passes through the light modulator 400, is directed in the direction of the Edge area of the light modulator 400 is deflected more towards the center of the viewing area of the display than the light from light sources in the center of the collimation optics 200. The light sources 101 - 123 can, as shown here, be arranged outside the focal plane of the collimation lenses 201 to 203, so that they are displayed in the middle viewing plane.

The individual light sources 101 - 123 can be composed of individually switchable or controllable sub-light sources with different spectral distributions of the emission characteristics. The individual sub-light sources can be slightly staggered in depth, i. H. at different positions in the direction of the optical axis in order to compensate for chromatic aberrations of the collimation optics so that all color components are imaged as far as possible in the same central viewing plane.

For this purpose z. B. the refractive power of the collimating lenses 201 to 203 can be variably changed by the system controller to such Compensate for color errors and adjust the viewing plane to the distance between the viewer and the display.

There are a number of other options for realizing a field lens function. The optical axis of the individual collimation lenses 201 to 203 could be inclined more and more towards the edge of the lens field 200, so that for example all optical axes cross in the middle of the viewing area in the central viewing plane. The light sources 101 to 123 assigned to a lens 201 to 203 can also be arranged at an angle.

4 shows the principle of guiding the observer by means of diffractive gratings on a section of an illumination device. A collimated light source 101 illuminates a switchable or controllable light influencing element 501 for beam deflection, which can contain at least one diffractive deflection grating, for example. Depending on the deflection angle set, this deflects the rays of the collimated light source 101 onto a different location on a focusing screen 110. The scattering profile can be varied locally in such a way that the best possible illumination of the following collimation lens 201, which z. B. can contain diffractive and / or refractive elements is achieved. The locally varying scattering profile of the screen 110 can be generated holographically, for example. Depending on the deflection angle, the points of impact of the light beams deflected by the light influencing element 501 form secondary light sources 111-113, which, via the collimation lens 201 of collimation optics, form a region of the light modulator analogously to 2 or 3 illuminate. Here, too, the light source 101 can consist of individually switchable sub-light sources with different spectral distributions of the emission characteristics. The light influencing element 500 can be composed of a plurality of deflection gratings in order to enable two-dimensional deflection, for example. Suitable screens 250 can be used to prevent light from unused orders of diffraction, which can arise at the light influencing element 501, or light from the secondary light sources 111 - 113, which does not fall on the collimation lens 201, from illuminating other collimation lenses of the collimation optics or from being unwanted scattered light in of the lighting device spreads.

Controllable diffractive gratings, in which the grating period can be set variably, can preferably be used as deflection gratings in the light influencing element 501 .

For example, phase gratings based on liquid crystal cells can be used for this, in which variable grating periods and thus deflection angles can be inscribed via a grid-like electrode structure.

Likewise, acousto-optical modulators can be used.

However, other design variants are also possible, such as the use of active and passive polarization gratings in conjunction with controllable delay plates.

Since the distance between the light influencing element 501 and the focusing screens 110 can be selected to be large, it is possible to use deflection gratings in the light influencing element 501, which can only produce small deflection angles. As a result, only low requirements are placed on the required minimum grating period, which considerably simplifies the production of such deflection elements.

The controllable grating can be illuminated obliquely in order to suppress unwanted intensities in the zeroth diffraction order. In order to obtain an optimal deflection range for each working wavelength, which largely overlaps, the grating can be illuminated with a different adjusted angle for each working wavelength range.

Instead of the deflection grid in the light influencing element 501, other deflection elements can also be used. For example, controllable electrowetting cells can be used in which the position of a meniscus or the position and shape of a meniscus as an interface between two liquids with different refractive indices can be varied in one or in two directions.

In 5 a section of a lighting device with a volume grating and angle multiplex of the light sources is shown symbolically. The light influencing element. 501, which contains at least one volume grating 502 for influencing the light, is illuminated from different directions by a plurality of light sources 101 - 103 via collimation optics 201 - 203 in directions that differ slightly from one another. Different reconstruction geometries are permanently encoded in the volume grating 502 of the light influencing element 501. When illuminated from different directions, different output wavefronts are generated. For example, the volume grating 502 of the light influencing element 501, which can also consist of a stack of multiple volume gratings 502, can be illuminated at five angles with an increment of 0.3°, which generate five field lens wavefronts on the output side with an angular increment of 12°, for example .

6 FIG. 12 shows schematically a light modulation device for a reflective light modulator 400 for image coding in connection with a front lighting device. The front illumination device for illuminating the light modulator 400 with collimated light contains a stack of planar light deflection elements 510, 520. The respective deflection function can be selected by activating a light source 110, 120 assigned to the respective light deflection element 510, 520. The light sources 110, 120 are formed in the example by at least one laser diode for the red 111, 121, the green 112, 122 and the blue 113, 123 spectral range. Via the collimation units 210, 220 assigned to the light sources 110, 120, their light is coupled via at least one volume grating 511, 521 into a flat optical waveguide 513, 523, which are each located on a substrate 514, 524. In the example, a hologram for the red, the green and the blue spectral range is written into the volume gratings 511, 521. For coherent-optical applications, for example a holographic display device, the planar optical waveguide 513, 523 should be chosen so thin that only one reflection angle (single-mode optical waveguide) can propagate in order to maintain the coherence properties of the light.

The light is coupled out of the volume grating 512, 522 assigned to the planar optical waveguides 513, 523 and directed onto the reflective light modulator 400 in a collimated manner. Depending on the selected light source 111-113, 121-123, the light modulated by the reflective modulator 400 is deflected in the desired direction by the associated volume grating 512, 522 or, as shown here in the example, is focused at the desired point in the viewing plane. In the example, holograms for each operating wavelength of the light sources 110, 120 are also written into the volume gratings 512, 522. The holograms are designed in such a way that a uniform illumination intensity is generated over the entire area of the light modulator 400 . For this purpose, the diffraction efficiency in the volume grating 512, 522 must increase the further away the coupling-out point is from the respective coupling-in grating 511, 521.

At least one additional light deflection element 600 working continuously or in fine steps ensures that, depending on the position of the viewer, the light can also be directed to eye positions that do not correspond to the fixed focusing points of the holograms inscribed in the volume gratings 512, 522. In this case, the deflection element 600 can support the field lens function or take over this function completely. Likewise, a separate field lens can be arranged, for example, between the light deflecting element 600 and the viewer.

The collimation units 210, 220 assigned to the light sources 110, 120 can contain passive and/or active optical elements 211, 212, 221, 222 for beam shaping and beam direction change, which can affect the light reflectively, diffractively and refractively. They can also contain scanning components in order, for example, to illuminate the in-coupling volume gratings 511, 521 in strips.

7 shows schematically a further embodiment variant of the invention. A controllable volume grating 532 can be used to control one of two field lenses inscribed in a static volume grating 533 by an in 7 not shown control panel are selected. A reflective phase modulator 400, which is illuminated in a collimated manner by a front illumination device 300, generates a modulated phase distribution which contains the image information to be displayed. In a beam combining optics 410, a wavefront 450 spatially modulated in amplitude and phase is generated by combining light, which was modulated by neighboring pixels of the phase modulator 400, for reconstructing the objects to be displayed in the reconstruction space. The object points can be real between the viewer and the light modulator 400 and virtual be reconstructed behind the light modulator 400. The modulated wave front 450 is deflected by the static volume grating 531 by a fixed angle in order to generate an optimal or suitable entrance angle for the following controllable volume grating 532 . The exit angles for the individual narrow-band wavelength ranges of the light sources of the front lighting device 300 can differ slightly from one another. Depending on the activation of the controllable volume grating 532, the light passes through it undiffracted or is diffracted at its grating structure into the first order of diffraction. The controllable volume grating 532 can be a polymer-dispersed liquid-crystal grating, for example. The desired diffraction pattern is generated during the manufacturing process by local polymerization when a hologram is written. Depending on the voltage applied to an electrode structure, the refractive index difference between the grating elements can be controlled in such a grating. If the voltage is chosen so that there is no difference in refractive index, the light passes through the grating without being diffracted. With a suitable voltage at the electrodes, the difference in refractive index in the grating can be selected in such a way that almost all light is diffracted into the first order for the current reconstruction wavelength range.

A static volume grating 533, which can also be designed as a multiplex volume grating, focuses the respectively selected direction in the focus area 1001 or 1002. The different entry angles for the individual wavelength ranges can also be taken into account, so that the focus areas of the individual colors each have a common focus area form.

It is also possible to locally vary the diffraction angles in the gratings 531 and/or 532 in order to locally obtain a suitable entrance angle for the volume grating 533 in order to set the required diffraction angle with high diffraction efficiency in this grating. A segmented arrangement can also be used here. The arrangement is also suitable for amplitude modulators or complex value modulators. Likewise, transmissive modulators can be used with a backlight device. For example, for an autostereoscopic display, the focus points for the right and left eye of the observer can be switched. As a rule, the arrangement is followed by a light influencing means (not shown here) for the continuous tracking of the foci to the observer position.

8th shows schematically an embodiment variant of a light modulator device with at least one transmissive phase modulator 400 for coding the image information in connection with a controllable liquid crystal phase grating 541. The light modulator 400 is illuminated with sufficiently coherent light with a background lighting device 300. The light modulated by the light modulator 400 is shaped in at least one beam combination optics 410 to form a wavefront 450 that is spatially modulated in amplitude and phase. This wavefront impinges on at least one controllable liquid crystal phase grating 541 for stepwise deflection of the wavefront. For this purpose, the liquid crystal phase grating 541 has a large number of electrodes which can be driven individually or in groups with a variable voltage profile. A Bragg grating is produced in the liquid crystal grating by applying a sawtooth-shaped voltage profile with variable period length and variable voltage swing to the electrode structure. Due to the resulting sawtooth curve of the phase profile on the grating, this acts as a blazed grating for the set deflection direction if the grating period and the phase shift are adapted to the current working wavelength. As a result, the light of the wavefront is diffracted in the desired deflection direction with high diffraction efficiency.

In general, the liquid crystal phase grating 541 can generate discrete or also continuously variable angles for, for example, three wavelengths.

In the subsequent field lens, which can contain a thin volume grating 542 and has a thick volume grating 543, one of the focus areas 1001 - 1005 written in the thick volume grating 543 is selected by the deflection angle selected with the liquid crystal phase grating 541 . The thin volume grating 542, if present, diffracts the light coming from the liquid crystal phase grating 541, so that an optimal or suitable entrance angle is created for the at least one thick volume grating 543, so that the light can be diffracted in the liquid crystal phase grating 541 with high diffraction efficiency.

A light influencing means 600, which contains at least one finely structured controllable diffractive liquid crystal phase grating, serves as a light influencing means for the continuous or finely graduated tracking of the selected focus area 1001-1005 to the position of the selected eye of the viewer by the in 8th control panel not shown. This forms the visibility area for viewing the reconstruction for the selected viewer's eye.

In 9 a light influencing means for the coarse beam deflection is shown schematically, which is integrated in a flat backlight unit. A light source 100 illuminates collimation optics 220 via beam expansion optics 210. The light source 100 can be z. B. contain at least one individually controllable laser diode for the red, the green and the blue spectral range. The light collimated by the collimation optics 220 is directed by a lens array 230 onto the aperture openings of an aperture array 120 in each case. The apertures act as secondary light sources and together form a light source array. Further optical components 110 for processing the light emitted by the light source 100 can be located in the beam path. For example, at least one moving screen can be positioned to reduce disruptive speckles, which modulates the coherent laser radiation with a random phase. Instead of a single light source 100 and the diaphragm field 120, a light source field containing, for example, a large number of laser diodes in the required wavelength ranges can also be used. The individual secondary light sources of the diaphragm field 120 are collimated via a further lens field 240 and illuminate a first light influencing element 550 for beam deflection in the vertical direction. Here, too, further optical components 130 can be located in the beam path for processing the the secondary light sources 120 emitted light are located. Thus, at least one fixed or moving screen can limit the spatial coherence on the output surface of the backlighting device to a suitable level, so that, for example, sub-holograms to be displayed do not influence one another. A second light influencing element 560 can influence the light in the horizontal direction. It is also possible for the light influencing elements 550, 560 to influence the light in a direction other than horizontal or vertical, or for them to be arranged in a different order. The light influencing elements 550, 560 can also be combined in one light influencing element with a two-dimensional light influencing effect. The light emanating from the light influencing means 550 illuminates a first volume grating 570 via a light guide 260. This directs the light via a further light guide 270 onto a second volume grating 580. Depending on the angular distribution of the light generated by the controllable light influencing elements 550, 560 with its selected wavelength distribution the desired angular spectrum for illuminating a light modulator (not shown here) is selected via the volume holograms written into the volume grating 570 and 580 . The angular distribution can be designed by the light influencing elements 550, 560 in such a way that the entire modulator surface is evenly brightly illuminated. To this end, the diffraction efficiency of the volume gratings 570, 580 can vary locally, as has already been described.

The light guides 260 and 270 should advantageously consist of a material whose refractive power differs as little as possible from that of the associated volume gratings 570 and 580 in order to avoid reflections at the interfaces. One or both of the light guides 260, 270 can also be wedge-shaped. However, they can also consist of other materials, such as air. In this case, the interfaces may have to be anti-reflective.

At the same time, the volume gratings 570 and 580 result in an anamorphic enlargement of the illumination wave field generated by the secondary light sources 120 and collimated by the lens field 240 . This makes it possible to use light influencing elements 550, 560 with a small spatial extent for the selection of the hologram functions written into the volume gratings 570 and 580. These can be produced more easily and cost-effectively than large-area arrangements. Small-area, controllable deflection gratings can also be produced with a smaller grating constant, as a result of which higher diffraction angles can be generated.

Further optical components such as optical fibers or deflection mirrors can be located in the light path between the light source 100 and the light guide 260 in order to enable a compact design of the overall system.

the 10a until 10c show schematically a possible structure and three exemplary possible effects of a light influencing element from the embodiment of FIG 9 using the light influencing element 550 for the vertical deflection.

Two successive controllable liquid crystal phase gratings 551 and 552 act as a vertical displacement unit and influence an input wavefront 150 and transform it into an output wavefront 160.

In the example of 10a the two controllable liquid crystal phase gratings 551 and 552 produce both a vertical shift and an angular change in the direction of propagation of the wave field 150.

Example according to 10b demonstrates an expansion and shift of the center of gravity of the wave field 150.

In the example according to the 10c there is a shift and locally varying change in the exit angle of the wave field 150.

In 11 a variant of a light modulation device is shown schematically, in which the tracking of the visibility range of the reconstruction of the 3D scene takes place in rough steps to the position of the viewer's eyes with the aid of a passive polarization grating in connection with active polarization-changing light influencing elements.

A phase modulator 400 that is sufficiently coherently illuminated by a backlight unit 300 and in which the scene to be reconstructed is encoded generates a wavefront 450 that is spatially modulated in amplitude and phase with the aid of beam combining optics 410. A switchable or controllable polarizer 591, which can be used, for example, as a switchable or If a controllable retardation plate can be formed, the light of the wave front 450 is selectively directed with right-hand or left-hand circular polarization onto the subsequent polarization grating 593. The polarization grating 593 diffracts the light into either the +1 or -1 diffraction order with high diffraction efficiency according to the polarization direction of the incident light. A volume hologram 592 can be arranged between the switchable polarizer 591 and the polarization grating 593 the switchable or controllable polarization-changing element locally diffracts light passing through in such a direction that it represents a suitable entrance angle for the polarization grating 593 .

A polarization-changing element 594, which can also be designed to be switchable or controllable, can be arranged behind the polarization grating 593 in order to suppress light that is not deflected into the desired diffraction order.

A subsequent light influencing means 600 for continuous or finely graduated light deflection directs the light of the modulated wavefront 450 onto the viewer's eyes, so that the viewer can perceive the reconstructed 3D scene.

The arrangement can contain further passive or active polarization-influencing elements in order to set the required polarization direction for subsequent polarization-dependent elements or to convert linearly polarized light into circularly polarized light or vice versa.

In the exemplary embodiment, a passive polarization grating 593 is shown, the grating period of which varies locally continuously or in steps. This allows, for example, a field lens function to be implemented. When the light influencing means 600 is in the neutral position, the light of the wavefront 450 is directed onto one of the two visibility regions 1001 or 1002, depending on the position of the switchable or controllable polarization-influencing elements 591 or 594. One or both switchable or controllable polarization-influencing elements 591 or 594 can also be structured locally and designed to be separately switchable or controllable in one or two directions in order to compensate for influences of the passage angle and/or the instantaneous wavelength range of the light passing through.

It is also possible to use polarization gratings 593 with a uniform grating constant. Depending on the position of the polarization-changing element 591, these direct the light of the modulated wavefront 450 in one of two directions, which are defined by the +1 and -1 diffraction order. The field lens function can then be achieved by additional passive and/or active optical elements, for example volume gratings will.

With locally controllable polarization-changing elements 591, 594, in stacks consisting of such elements 591, 594 and passive polarization gratings 593, the influence of the deflection angle of elements 591, 593, 594 of the stack planes arranged in front of them in the beam path can be wavelength-dependent on the polarization change in the respective polarization-influencing Compensate element 591, 594. Polarization-influencing elements 594 and 591, which follow one another and belong to different adjacent stack levels, can also be combined in a common controllable polarization-influencing element.

Such stacks can be used to generate more than two focus areas or deflection directions. The polarization gratings 593 in the stacking planes preferably have different grating constants and thus different diffraction angles at the same horizontal and vertical position in order to achieve the most uniform and finest possible gradations overall, so that double focus areas are avoided.

By using polarization gratings 593 with a controllable grating period, the number of layers in such a stack can be kept small.

With switchable polarization gratings 593, the zeroth diffraction order can also be used.

By a suitable combination of the layer thickness and thus the optical retardation and the twist angle of the liquid crystal molecules, polarization gratings 593 can be produced which have a diffraction efficiency of almost 100% for a wide wavelength range. Stacks of switchable polarization gratings 593 can also be used, in which each element is optimized for a different wavelength range.

In color multiplex operation, only the grating optimized for the current spectral range can be activated.

Instead of a phase modulator 400 and beam combining optics 410, a complex-valued light modulator can also be used. It is also possible to use a reflective modulator in conjunction with front lighting.

In the exemplary embodiments listed, light modulators can also be used which generate the encoded hologram via a scanning device or which contain a number of light modulators. Likewise, a holographic or an autostereoscopic display can also contain several separate light modulator devices that jointly reconstruct a 3D scene or generate a stereoscopic image.

In all examples, all active components can be controlled by a system controller based on the positions of the observer's eyes determined by an eye position detection system. B. image errors of optical components, temperature influences and local deviations in the wavefront shape due to brightness deviations in the lighting device 300 and modulation errors in the light modulator 400 can be largely taken into account and compensated. If necessary, such errors can be determined by calibration measurements or actively measured in real time.

Finally, it should be particularly pointed out that the exemplary embodiments discussed above only serve to describe the teaching claimed, but do not restrict it to the exemplary embodiments.

Claims (18)

Light modulation device for a holographic or an autostereoscopic display for displaying three-dimensional image information with at least one real or virtual light source (100), at least one light modulator (400) for encoding the image information to be displayed for at least one viewer eye (1100) of at least one viewer, a first light influencing means ( 500) and a second light influencing means (600), different from the first light influencing means (500), for changing the light path of the light emitted by the light source (100), an eye position detection system (800) for detecting and tracking at least one eye position of the at least one viewer of the image information and one System controller (900) for tracking at least one visibility region (1000) of the image information based on the eye position data (901) supplied by the eye position detection system with the aid of the first and the second light element Influencing means (500, 600), characterized in that the first light influencing means (500) has a switchable polarization-influencing element (591) and a polarization grating (593), that in the light propagation direction the switchable polarization-influencing element (591) is arranged in front of the polarization grating (593), that the polarization grating (593) according to the polarization direction of the incident light and depending on the position of the switchable polarization-influencing element (591) the light either in a +1. or into a -1. Diffraction order diffracts that with the first light influencing means (500) the visibility range (1000) within a viewer range can be tracked to the eyes of the viewer in rough steps, and that the second light influencing means (600) the visibility range (1000) at least in the range of a rough step of the first Light influencing means (500) finely graded or continuously tracks the eyes of the viewer (1100) with the aid of at least one electrically controllable diffraction grating. light modulation device claim 1 , characterized in that in the light propagation direction the second light influencing means (600) is arranged in front of or behind the first light influencing means (500) and in that the first and/or second light influencing means (500, 600) is arranged in front of or behind the light modulator (400). light modulation device claim 1 or 2 , characterized in that the beam direction of the light path can be changed with the first (500) and/or the second light influencing means (600). Light modulation device according to one of the preceding claims, characterized in that the first and/or the second light influencing means (500, 600) is composed of a plurality of light influencing elements with which the beam direction can be changed independently of one another. Light modulation device according to one of the preceding claims, characterized in that the size of the beam direction change in the first and/or in the second light influencing means (500, 600) can be changed depending on the point at which the light hits the surface of the light influencing means (500, 600), so that in addition a field lens function of fixed or variable focal length can be implemented for the tracking function or such a field lens function is supported. Light modulation device according to one of the preceding claims, characterized in that a change in the position of at least one light source (100) in the first light influencing means can be implemented by a mechanical movement of the at least one light source (100) and/or by modulating the intensity of a plurality of light sources (100) at different locations . Light modulation device according to one of the preceding claims, characterized in that there is at least one first light influencing means (500) which influences the light diffractively. light modulation device claim 1 , characterized in that further passive or active polarization influencing elements (594) are included in order for subsequent polarisa tion-dependent elements to set the required polarization direction or to convert linearly polarized light into circularly polarized light or vice versa. light modulation device claim 1 or 8th , characterized in that the polarization influencing element (591) and/or the further switchable polarization influencing element (594) is designed as a switchable or controllable retardation plate. Light modulation device according to Claim 1 or 8 or 9, characterized in that the polarization grating (593) is designed as a passive polarization grating and that the polarization grating (593) has a grating period which locally varies continuously or in steps, or the polarization grating (593) has a uniform grating period having. light modulation device claim 1 , characterized in that the polarization grating (593) has a controllable grating period or that the polarization grating (593) is designed to be switchable. Light modulation device according to one of the preceding claims, characterized in that the first light influencing means (500) contains at least one switchable delay plate and at least one birefringent lens in order to change the beam direction of the light. light modulation device claim 12 , characterized in that at least one birefringent lens is a liquid crystal lens. Light modulation device according to one of Claims 12 or 13 , characterized in that there is at least one birefringent polarization grating (593) with a fixed grating period or a grating period that varies over the surface of the polarization grating in order to change the beam direction of the light. Light modulation device according to any one of the preceding Claims 1 until 7 , characterized in that in the first light influencing means (500) there is at least one birefringent polarization grating (593) with a switchable fixed grating period or one that varies over the surface of the polarization grating in order to change the beam direction of the light sources. light modulation device claim 15 , characterized in that at least one birefringent switchable polarization grating (593) is present, which has been optimized for oblique incidence of light and/or which has achromatic properties and is optimized for at least two wavelengths. Light modulation device according to one of the preceding claims, characterized in that in the second light influencing means (600) there is at least one changeable diffractive grating with which the beam direction changes can be adjusted by the controllable uniform or locally variable change in a grating period of the diffractive grating. light modulation device Claim 17 , characterized in that at least one of the changeable diffractive gratings contains a liquid crystal layer whose locally fixed or variable grating period is changed by applying the voltage profile to an electrode structure.

Images