Abstract:
A novel spatio-optical directional light modulator with no moving parts is introduced. This directional light modulator can be used to create 2D/3D switchable displays of various sizes for mobile to large screen TV. The inherently fast modulation capability of this new directional light modulator increases the achievable viewing angle, resolution, and realism of the 3D image created by the display.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 61/567,520 filed Dec. 6, 2011. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Directional light modulation, 3D displays, emissive micro displays, 2D/3D autostereoscopic switchable displays. 
     2. Prior Art 
     In some switchable 2D/3D displays a directional backlight is necessary to operate the display in different display modes. In a 2D display mode, a backlight with uniform illumination and large angular coverage is required to display a single image with spatial light modulators (such as liquid crystal displays (LCD)). In a 3D display mode, a backlight with uniform illumination and multiple illumination directions is required to display images of the same scene from different directions by utilizing some combination of spatial multiplexing and temporal multiplexing in the spatial light modulator. 
     In both 2D and 3D modes, the light that comes from the directional backlight is usually processed by a directionally selective filter (such as diffractive plate, a holographic optical plate etc.) before it reaches the spatial light modulator pixels to expand the light beam uniformly while keeping its directionality. 
     Currently available directional light modulators are a combination of an illumination unit comprising multiple light sources and a directional modulation unit that directs the light emitted by the light sources to a designated direction (see  FIG. 3 ). An illumination unit is usually combined with an electro-mechanical movement device such as rotating mirrors or rotating barriers (see U.S. Pat. Nos. 6,151,167, 6,433,907, 6,795,221, 6,803,561, 6,924,476, 6,937,221, 7,061,450, 7,071,594, 7,190,329, 7,193,758, 7,209,271, 7,232,071, 7,482,730, 7,486,255, 7,580,007, 7,724,210, and 7,791,810 and U.S. Patent Application Publication Nos. 2010/0026960 and 2010/0245957), or electro-optical device such as liquid lenses or polarization switching (see FIG. 1 and FIG. 2 and U.S. Pat. Nos. 5,986,811, 6,999,238, 7,106,519, 7,215,475, 7,369,321, 7,619,807 and 7,952,809). 
     In both electro-mechanically and electro-optically modulated directional light modulators there are three main problems: 
     1. Speed: When electrical energy is used to create mechanical movement or optical change, the movement or change is not achieved instantaneously. Usually a type of acceleration, deceleration and stabilization has to be achieved to reach the desired mechanical or optical state. The speed of these operations usually takes up a significant portion of the frame time that reduces the efficiency and limits the achievable display brightness. 
     2. Volumetric thickness of the device: Both of these methods need a distance between the light source and directional modulation device to work with, which increases the total thickness of a display. 
     3. Light loss: Coupling light on to a moving mirror assembly or using a liquid lens with adjustable focal length creates a light loss on the order of 50% to 90% which in turn requires more power consumption to compensate for the light loss, and creates heat in the system that has to be eliminated by a cooling method. 
     In addition to being slow, bulky and optically lossy, the prior art directional backlight units need to have narrow spectral bandwidth, high collimation and individual controllability for being combined with a directionally selective filter for 2D-3D switchable display purposes. Achieving narrow spectral bandwidth and high collimation requires device level innovations and optical light conditioning, increasing the cost and the volumetric aspects of the overall system. Achieving individual controllability requires additional circuitry and multiple light sources, increasing the system complexity, bulk and cost. 
     It is therefore an objective of this invention to introduce a spatio-optical light modulator that overcomes the drawbacks of the prior art, thus making it feasible to create 3D displays that provide practical volumetric and viewing experience. Additional objectives and advantages of this invention will become apparent from the following detailed description of a preferred embodiment thereof that proceeds with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like reference numerals refer to similar elements. 
         FIG. 1  illustrates a prior art directional light modulator that uses liquid lens. 
         FIG. 2  illustrates a prior art directional light modulator that uses rotating mirrors. 
         FIG. 3  illustrates a prior art directionally modulated 3D light modulator. 
         FIG. 4  is a two dimensional view of the directional light modulation principle of the spatio-optical directional light modulator of this invention. 
         FIG. 5  is an isometric view of the directional light modulation principle of the spatio-optical directional light modulator of this invention. 
         FIG. 6  illustrates an exemplary collimating wafer level optics design of the spatio-optical directional light modulator of this invention. 
         FIG. 7  illustrates an exemplary design of the spatio-optical directional light modulator of this invention that uses wafer level optics exemplary design illustrated in  FIG. 6 . 
         FIG. 8  illustrates the directional modulation range of an exemplary embodiment of the spatio-optical directional light modulator of this invention. 
         FIG. 9  illustrates the angular addressability in 3D space for an exemplary embodiment of the spatio-optical directional light modulator of this invention. 
         FIG. 10  is a block diagram explaining the data processing block diagram of the spatio-optical directional light modulator of this invention. 
         FIG. 11  is an isometric view of an exemplary embodiment of the spatio-optical directional light modulator of this invention implemented by tiling a multiplicity of the exemplary design illustrated in  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     References in the following detailed description of the present invention to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristics described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in this detailed description are not necessarily all referring to the same embodiment. 
     A new class of emissive display devices called Quantum Photonic Imagers (QPI™, a trademark of Ostendo Technologies, Inc.) has been recently introduced (see U.S. Pat. Nos. 7,623,560, 7,767,479, 7,829,902 and 8,049,231 and U.S. Patent Application Publication Nos. 2009/0086170, 2009/0278998, 2010/0003777, 2010/0066921, 2010/0091050 and 2010/0220042). The QPI devices feature high brightness, very fast light amplitude modulation and spatial modulation capabilities in a very small device volume that includes all the driver circuitry. 
     The present invention combines the emissive micro array capabilities of the QPI device with passive wafer level optics (WLO) to create a light modulator that can perform the functionalities of a directional light source and a diffractive plate at the same time. As used herein, wafer level or wafer means a device or matrix of devices having a diameter of at least 2 inches, and more preferably 5 inches or more. WLO are fabricated monolithically on the wafer from polymer using ultra violet (UV) imprint lithography. Among primary advantages of WLO are the ability to fabricate micro lens arrays and to be able to precisely align multiple WLO optical elements together and with an optoelectronics device such as a CMOS sensor or the QPI device. The alignment precision that can be achieved by a typical WLO fabrication technique can be less than one micron. The combination of the digitally addressable emissive micro emitter pixel array of the QPI device and the WLO micro lens array (MLA) that can be precisely aligned with respect to the micro emitter array of the QPI device eliminates the need for having a directionally selective filter in the system while relaxing the requirement for the narrow spectral bandwidth in the light source, reducing the system volume, complexity and cost simultaneously. 
     With a fine pitch wafer level collimating MLA, the light emitted from the QPI device micro emitter array of pixels can be modulated directionally as illustrated in  FIG. 4  and spatially as illustrated in  FIG. 5 .  FIG. 4  illustrates the directional modulation principle of the present invention. As illustrated in  FIG. 4 , a multiplicity of the individually addressable light emitting pixels Pixel  1 , Pixel  2 , . . . , Pixel-n (p 1 , p 2 , . . . , p n ) of the QPI device are associated with a single micro lens of the MLA. Referring to  FIG. 1 , the light from p 1  would be refracted by the wafer level micro lens and traverse to d 1 , the light from p 2  would be refracted by the wafer level micro lens and traverse to direction d 2  and the light from p n  would refracted by the wafer level micro lens and traverses to d n  whereby directions Direction-1, Direction-2, . . . , Direction-n (d 1 , d 2 , . . . , d n ) are distributed directionally across the numerical aperture of the micro lens. With the individual addressability of QPI device pixels p 1 , p 2 , . . . , p n , the directions of emitted light into the directions d 1 , d 2 , . . . , d n  become also individually addressable. 
       FIG. 5  illustrates the spatial and directional modulation principles of the present invention.  FIG. 5  illustrates a 2-dimensional array comprising a multiplicity of QPI device pixel groups G 1 , G 2 , . . . , G N  with each such pixel group associated with one micro lens of a wafer level micro lens array (MLA). With the one-to-one association of the individual pixels p 1 , p 2 , . . . , p n  within each group with the emitted light directions d 1 , d 2 , . . . , d n , it becomes possible for the light emitting device illustrated in  FIG. 5  to generate light that can be spatially and directionally modulated. Thus the light can be emitted from each of the spatial locations in the emissive area of the QPI device pixel groups G 1 , G 2 , . . . , G N  and be individually addressable through the addressability of the pixel groups as well as the directionally addressable through the addressability of the individual pixel within each pixel group. The individual pixels of the QPI device can be modulated so that each lens in the MLA can emit light to multiple directions simultaneously. Because of individual pixel control, the light amplitude, the time duration of the light emission, the specific light direction and the total number of light directions emitted from each micro lens can be individually adjusted through the individual addressability of the QPI device pixels. 
     It is obvious to a person skilled in the art that the directional modulation by a lens can be done on a single axis, or on two axes with the choice of lens type (i.e., lenticular lens array or two-axis lens array). However, precise alignment of the lens array with the pixelated light source and the achievability of small pixel size (in the order of few microns, or 10 microns or less) have prevented the realization of a directional light modulator that can generate the directional light modulation capabilities needed to create high definition 3D displays. In the present invention the high pixel resolution is achieved by leveraging the emissive micro pixel array of the QPI device, which can attain less than 10 micron pixel pitch, and the high precision alignment of lens array, which can be less than one micron, made possible by the wafer level optics. This allows the spatio-optical light modulator of this invention to achieve the spatial as well as directional modulation resolution sufficient to realize a high definition 3D displays. 
       FIGS. 6 and 7  show an exemplary embodiment of the present invention. Referring to  FIG. 6  of this exemplary embodiment, the light emitted from each individual pixel within a pixel group G i  travels from the QPI device emissive surface to the exit aperture of a micro lens that comprises the three optical elements  610 ,  620  and  630 . The light emitted from each individual pixel within a pixel group G i  would be collimated and magnified to fill the exit aperture of the WLO micro lens system  610 ,  620  and  630  and traverses at a specific direction within a Θ=±15° angular divergence. In essence the micro lens system  610 ,  620  and  630  would map the light emitted from the individual pixels of the two dimensional pixel group G i  comprising the QPI device into individual directions within the three dimensional volume defined by Θ=±15° angular divergence of the WLO micro lens system  610 ,  620  and  630 . 
     Referring to  FIG. 6  of the exemplary embodiment, a multiplicity of the micro lens elements  610 ,  620  and  630  are fabricated to form a micro lens arrays  710 ,  720  and  730  which would be precisely aligned relative to each other and relative to the associated arrays of the QPI device pixel groups G 1 , G 2 , . . . , G N . The exemplary embodiment illustrated in  FIG. 7  also includes the QPI device  750  and its associated cover glass  760 . The design of the micro lens elements  610 ,  620  and  630  would take into account the thickness and optical characteristics of the QPI device cover glass  760  in order to image the emissive surface of the QPI device  760 . The exemplary embodiment of  FIG. 7  illustrates the full assembly of the spatio-optical directional light modulator of this invention. The typical total thickness of the exemplary embodiment of the spatio-optical directional light modulator of this invention illustrated in  FIG. 7  would be less than 5 millimeters. Such compactness of the directional light modulator of this invention is not possibly achievable by directional light modulation techniques of the prior art. 
       FIG. 8  and  FIG. 9  illustrate the operational principles of the spatio-optical directional light modulator of this invention.  FIG. 8  illustrates an exemplary embodiment of one of the modulation groups G i  being comprised of a two dimensional array of (n×n) of the emissive pixels of the QPI device whereby for convenience the size of the pixel group G i  along one axis would be selected to be n=2 m . Referring to  FIG. 8 , the directional modulation addressability that can be achieved by the pixel group G i  would be accomplished through the addressability of the pixels comprising the modulation group G i  along each of its two axes x and y using m-bit words.  FIG. 9  illustrates the mapping of the light emitted from (n×n) pixels comprising the QPI device pixel group G i  into individual directions within the three dimensional volume defined by angular divergence ±Θ of the associated WLO micro lens such as that of the exemplary embodiment  600 . As an illustrative example, when the dimensions of the individual pixels of the QPI device are (5×5) microns and the QPI device pixel group is comprised of (n×n)=(2 8 ×2 8 )=(256×256) pixel array and the angular divergence of the associated WLO micro lens is Θ=±15°, then from each of the QPI device two dimensional modulation pixel groups G i  of size (1.28×1.28) millimeter at the QPI device emissive surface it would be possible to generate (256) 2 =65,536 individually addressable directional light beams spanning the angular divergence of Θ=±15° whereby the light generated in each of the 65,536 directions can be individually modulated in color and intensity as well, typically using a relatively high frequency pulse width modulation of each pixel color component, though other control techniques could be used if desired, such as proportional control. 
     Any desired spatial and directional modulation capabilities for the QPI device based spatio-optical directional light modulator of this invention would be possible using an array of (N×M) of the directional modulation groups G i  such as that described in the previous design example. If, for example, it is required to create a spatio-optical directional light modulator with spatial modulation resolution of N=320 by M=240 that provides (256) 2 =65,536 directional modulation resolution, the spatio-optical directional light modulator of this invention would comprise an array of (320×240) directional modulation groups and when a QPI device with (5×5) micron pixel size is used, the total size of the spatio-optical directional light modulator would be approximately 41×31 cm. The light emitted from such a spatio-optical directional light modulator can be spatially modulated at a resolution of (320×240) and directionally modulated at a resolution of 65,536 within the angular divergence ±Θ associated with its WLO micro lens array (for example Θ=±15° for the exemplary embodiment  600 ) and can also be modulated in color and intensity in each direction. 
     The resolution of the directional modulation of the light modulators of this invention in terms of the number of individually addressable directions within the angular divergence ±Θ of the wafer level micro lens array would be determined by selecting either the pixel pitch of the emissive micro emitter array QPI device or by selecting lens pitch of the wafer level micro lens array, or a combination of the two. It is obvious to a person skilled in the art that the lens system, such as that illustrated in  FIG. 6 , can be designed to allow either wider or narrower angular divergence ±Θ. It is also obvious to a person skilled in the art that either a smaller or a larger number of pixels within each modulation group G i  can be used to generate any desired directional modulation resolution. 
     Depending of the total pixel resolution of the QPI device used, such a spatio-optical directional light modulator can be implemented using a tiled array comprising a multiplicity of QPI devices. For example if a QPI device with (1024×1024) pixel resolution is used, then each such QPI device can be used to implement an array of (2×2) modulation groups G i  and the spatio-optical directional light modulator having (6×6) spatial light modulation resolution and 65,536 directional light modulation resolution would be implemented using a tiled array (3×3) of such QPI devices such as in the illustration of  FIG. 11 . 
     The tiling of an array of QPI devices to implement the spatio-optical directional light modulator of this invention is made possible because of the compactness that can be achieved by the emissive QPI devices and the associated WLO. For example, with an implementation such as that illustrated in  FIG. 7 , it would be possible to fabricate a QPI device/WLO assembly such as that illustrated in  FIG. 7  with width, height and thickness of 5.12×5.12×5 millimeters; respectively, to realize the (2×2) modulation group spatio-optical directional light modulator of the previous example. It would also be possible to implement such a QPI device/WLO assembly with its electrical interfaces being a micro ball grid array (MBGA) located at the opposite side of its emissive surface, which would allow the entire top surface of the QPI device/WLO assembly to constitute the emissive surface of the device, which in turn would make it possible to seamlessly tile multiplicity of such QPI device/WLO assemblies to implement any desired size of the spatio-optical directional light modulator of this invention.  FIG. 11  is an illustration of the tiling of multiplicity of the QPI device/WLO assemblies to implement an arbitrary size of the spatio-optical directional light modulator of this invention. 
     The principle of operation of the spatio-optical directional light modulator of this invention will be described in reference to the illustrations of  FIGS. 8 and 9 .  FIG. 8  illustrates the two dimensional addressability of each of the modulation groups G i  using m-bit resolution for the directional modulation. As explained earlier, light emitted from (2 m ×2 m ) individual pixels in an n×n array of the modulation group G i  is mapped by its associated WLO elements into 2 2m  light directions within the angular divergence ±Θ of the associated WLO micro lens. Using the (x,y) dimensional coordinates of the individual pixels within each of the modulation groups G i , the angular coordinates (θ,φ) of the emitted light beam is given by: 
     
       
         
           
             
               
                 
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                   Equation 
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                   Equation 
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     Where the angles (θ, φ) are spherical coordinates with the polar axis at θ=0 parallel to the z axis of the emissive surface of the modulation group G i  and m=log 2  n is the number of bits used to express the x and y pixel resolution of the modulation group G i . 
     The spatial resolution of the spatio-optical directional light modulator of this invention is simply defined by the coordinates of each of the individual modulation group G i  within the two dimensional array of modulation groups comprising the overall spatio-optical directional light modulator. There is of course, some cross talk between pixels of one group and the micro lens for an adjacent group. However the cross talk is substantially reduced by the following design aspects. First, because of the inherently collimated light emission of the QPI device, the light emitted from the QPI device pixels is typically confined to a ±17° cone for the case when the QPI device pixels are light emitting diode or to a ±5° cone for the case when the QPI device pixels are laser diodes. Thus placing the wafer level optics (WLO) collimation lens elements close to the emissive surface  660  of the QPI device as illustrated in  FIG. 6  will make most of the light emitted from each modulation group edge pixels be confined to its associated WLO lens element  600 . Second, as an added measure, a few (some) edge pixels of each pixel group are turned off to further avoid leakage of light (cross-talk) between adjacent lenses of the WLO micro lens array. For example, given the ±17° confined emission of the QPI device with its pixel arc light emitting diodes and the close placement of the first micro lens element as illustrated in  FIG. 6 , simulation shows that a dark ring around the outer edge of the modulation group comprising as few as only 5 pixels will reduce the cross-talk to below 1%. When the QPI device pixels are laser diodes, the required number of turned off pixels will be even less and may be not even required since in this case the QPI device pixel light emission is confined to an even much narrower ±5° cone. The end result may be some (a few) inactive, blank or dead pixel positions between active pixels in the QPI devices in the array. Of course baffles and/or band-limiting light diffusers could be used if desired, though they tend to complicate the design of the light modulator and cause excessive loss of light. 
       FIG. 10  illustrates exemplary embodiment of the data processing block diagram of the spatio-optical directional light modulator of this invention. The input data to the spatio-optical directional light modulator of this invention will be formatted in multiple bit words whereby each input word contains the three fields; one field being the address of modulation group G i  within the modulation group array comprising the spatio-optical directional light modulator while the remaining two data fields provide the data representation of the light to be emitted from that modulation group in terms of its color, intensity and direction. Referring to  FIG. 10 , the data processing block  120  decodes the modulation group address field of the input data and routes the light modulation data fields to the QPI device associated with the designated modulation group. The data processing block  130  decodes the routed modulation group address field and maps it to the address of the designated modulation group. The data processing block  140  decodes the directional modulation data field and maps it into the designated pixel address within the modulation group. The data processing block  150  concatenates the resultant pixel address with the associated light intensity and color data fields of the input data. The data processing block  160  decodes the designated pixel address and routes the light modulation data to the designated pixel within the designated QPI device comprising the spatio-optical directional light modulator. 
     In using the directional modulation resolution of 16-bit of the previously described example and the typical 24-bit of resolution for representing the modulated light intensity and color in each direction, the total number bits that would represent the modulation data word for each modulation group would be 40-bit. In assuming, without loss of generality, that such 40-bit words would be inputted to the spatio-optical directional light modulator of this invention for addressing its constituent modulation groups sequentially; i.e., sequential addressing is used to input the modulation group data 40-bit words. Block  120  of  FIG. 10  would be responsible for routing the sequentially inputted data word to the designated QPI device. Block  130  of  FIG. 10  would be responsible for routing the modulation data to the designated modulation group. Block  140  of  FIG. 10  would be responsible for mapping the 16-bit directional modulation data field into the designated address of the pixel with the designated modulation group. Block  150  of  FIG. 10  would be responsible for concatenating the 24-bit light intensity and color data with the mapped pixel group address. Block  160  of  FIG. 10  would be responsible for routing the 24-bit light intensity and color modulation data to the designated pixel within the designated QPI device comprising the spatio-optical directional light modulator. With this exemplary data processing flow of the 40-bit word sequential data input, the spatio-optical directional light modulator of this invention would modulate the light emitted from its aperture in intensity, color and direction based on the information encoded with its input data. The light intensity and color modulation may be, by way of example, pulse width modulation of the on/off times of the multi color pixels to control the average intensity of the light and to control the intensity of each color component making up the resulting color, though other control techniques may be used if desired. In any event, the direction and intensity are controlled, and color, direction and intensity are controlled in a multi color system. 
     Possible Applications 
     The spatio-optical directional light modulator of this invention can be used as a backlight for liquid crystal display (LCD) to implement a 3D display. The spatio-optical directional light modulator of this invention by itself can be used to implement a 3D display of an arbitrary size that is realized, for example, as a tiled array of multiplicity of QPI devices/WLO assemblies such as that illustrated in  FIG. 10 . The light modulator of this invention can also be operated as a 2D high resolution display. In this case the individual pixels of the QPI device would be used to modulate the color and intensity while its integrated WLO would be used to fill the viewing angle of the display It is also possible for the light modulator of this invention to be switched from 2D to 3D display modes by adapting the format of its input data to be commensurate with the desired operational mode. When the light modulator of this invention is used as a 2D display, its light angular divergence will be that associated with its WLO micro lens array ±Θ and the pixel resolution of the individual modulation group G i  will be leveraged to achieve higher spatial resolution. 
     Thus the present invention has a number of aspects, which aspects may be practiced alone or in various combinations or sub-combinations, as desired. While certain preferred embodiments of the present invention have been disclosed and described herein for purposes of illustration and not for purposes of limitation, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the full breadth of the following claims.