Abstract:
An apparatus, system, and method for subpixels of a light valve pixel having characteristics adapted to complement light within certain wavelength ranges are disclosed herein.

Description:
RELATED APPLICATION  
       [0001]     This is a continuation of co-pending U.S. patent application Ser. No. 11/060,939 filed on Feb. 18, 2005 titled “Optical Assembly to Provide Complementary Illumination of Subpixels of a Light Valve Pixel.” 
     
    
     FIELD OF THE INVENTION  
       [0002]     Embodiments of the invention relate generally to the field of projection systems, and more particularly to designs of subpixels of a light valve pixel for use in such systems.  
       BACKGROUND OF THE INVENTION  
       [0003]     Multimedia projection systems have become popular for purposes such as conducting sales demonstrations, business meetings, classroom training, and for use in home theaters. In typical operation, multimedia projection systems receive analog video signals from a video unit and convert the video signals to digital information to control one or more digitally driven light modulators. Depending on the cost, brightness, and image quality goals of the particular projection systems, the light modulators may be of various sizes and resolutions, be transmissive or reflective, and be employed in single or multiple light path configurations.  
         [0004]     Many light modulators used in projection and direct viewing systems operate on the basis of polarization. Such light modulators may include reflective or transmissive light valves based on liquid crystal technology. These liquid crystal light valves can produce a high-resolution image by changing the polarization state upon reflection or transmission of incident light. A polarization-analyzing device may then propagate the light from a bright state pixel of the light valve as a display image to be viewed by the human eye or projected onto a viewing screen.  
         [0005]     There are several different optical architectures for employing liquid crystal light valves. One variation is a multipath optical architecture that provides a separate path for each of the primary color (red, blue, and green) lights. Polychromatic light is optically divided to provide each of the three pathways with its associated color light. The different color lights are routed through a series of polarization beam splitters, filters, and wave plates to a color-specific light valve. Each of the light valves is controlled with its respective color data in order to manipulate the colored light into image bearing light. The individual pathways are then reconverged into a color image. Although this design produces an acceptable image, the optics required for the color divergence, separate modulation, and reconvergence are expensive and costly to implement.  
         [0006]     Another variation is a single-path multimedia projector. This type of projector involves only one light path that is sequentially illuminated with primary colors that time-share the same liquid crystal light valve. One alternative of this architecture employs a light source to produce polychromatic light rays, which are then directed through color filter segments of a color wheel. This filtering out of the nonselected color provides resource waste that could increase power consumption or decrease the brightness of the projected image.  
         [0007]     Another alternative of the single-path multimedia projector employs monochromatic solid-state light sources, such as light-emitting diodes, to selectively emit the primary colors. This alternative requires expensive color combining optics in order to make the three color light beams coaxial before illuminating the liquid crystal light valve. Also, because the solid-state light sources are pulsed at 1/3 duty ratio the lumens/watt efficiency drops as the drive current increases.  
         [0008]     A promising alternative to the above-mentioned optical architectures involves a microlens array that is optically coupled with the liquid crystal light valve. This microlens array receives the primary colored light along three ranges of incident angles and focuses the primary colors onto separate subpixels of each individual pixel. The subpixels can simultaneously and selectively modulate the individual colors in order to transmit a colored image. The promises of the microlens alternative, however, are tempered by inefficiencies due to light processing characteristics of prior art systems. These inefficiencies may result directly or indirectly from color separation, polarization filtering, and/or underfilling the subpixels. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     Embodiments of the invention are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings, in which like references indicate similar elements and in which:  
         [0010]      FIG. 1  is a simplified block diagram of an illumination module, optical assembly, and a pixel, in accordance with an embodiment of the present invention;  
         [0011]      FIG. 2  illustrates a side view of a lens focusing light on subpixels, in accordance with an embodiment of the present invention;  
         [0012]      FIG. 3  illustrates the illumination incident upon subpixel apertures, in accordance with an embodiment of the present invention;  
         [0013]      FIG. 4  illustrates illumination incident upon a number of pixels of a light valve display, in accordance with another embodiment of the present invention;  
         [0014]      FIG. 5  illustrates a side view of an optical architecture with angular color separated illumination, in accordance with an embodiment of the present invention;  
         [0015]      FIG. 6  illustrates a top view of an optical architecture with a polarization recycling assembly, in accordance with an embodiment of the present invention; and  
         [0016]      FIG. 7  illustrates the illumination incident upon subpixel apertures, in accordance with an embodiment of the present invention;  
         [0017]      FIG. 8  illustrates a top view of an optical architecture with a polarization recycling assembly, in accordance with another embodiment of the present invention;  
         [0018]      FIG. 9  is a simplified block diagram of a projection system in accordance with an embodiment of the present invention; and  
         [0019]      FIG. 10  illustrates the illumination incident upon subpixel apertures with difference characteristics, in accordance with another embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0020]     Illustrative embodiments of the present invention include an optical assembly adapted to provide complementary illumination to subpixels of light valve pixel, and methods practiced thereon.  
         [0021]     Various aspects of the illustrative embodiments will be described using terms commonly employed by those skilled in the art to convey the substance of their work to others skilled in the art. For purposes of explanation, specific materials and configurations are set forth in order to provide a thorough understanding of the illustrative embodiments. However, it will be apparent to one skilled in the art that alternate embodiments may be practiced without the specific details. In other instances, well-known features are omitted or simplified in order not to obscure the illustrative embodiments. In particular, a wide variety of optical components such as prisms, mirrors, lenses, integration elements, etc. may be used as appropriate to fold, bend, or modify the illumination for the intended application. Integration of these optical components into illustrated embodiments may not be specifically addressed unless it is necessary to develop relevant discussion of embodiments of the present invention.  
         [0022]     Further, various operations will be described as multiple discrete operations, in turn, in a manner that is most helpful in understanding the present invention; however, the order of description should not be construed as to imply that these operations are necessarily order dependent. In particular, these operations need not be performed in the order of presentation.  
         [0023]     The phrase “in one embodiment” is used repeatedly. The phrase generally does not refer to the same embodiment; however, it may. The terms “comprising,” “having,” and “including” are synonymous, unless the context dictates otherwise.  
         [0024]      FIG. 1  illustrates a simple block diagram of an optical architecture  100 , in accordance with an embodiment of the present invention. In brief, an illumination module  104  may provide randomly polarized light to an optical assembly  108 . Randomly polarized light may be indicated in the figures by Xs in the optical paths. The randomly polarized light may be in the form of colored illumination bundles  112 ,  114 , and  116 . Each of the illumination bundles  112 ,  114 , and  116  may include a first and a second polarization state, e.g., a P-polarized portion and a, largely orthogonal, S-polarized portion. The optical assembly  108  may include components adapted to receive the illumination bundles  112 ,  114 , and  116  and transmit, e.g., the P-polarized portions  112 ′,  114 ′, and  116 ′ to a light valve pixel  120 . P-polarized light may be indicated in the figures by short transverse lines in the light paths, suggesting a polarization vector in the plane of the drawing sheet.  
         [0025]     In one embodiment, the illumination bundles  112 ,  114 , and  116  may each be of a primary color such as red, green, or blue. In this embodiment, the pixel  120  may be a liquid crystal pixel with selectively controlled electrodes designed to spatially address subpixels  124 ,  126 , and  128 . The electrodes, and thereby the corresponding subpixels, may be activated with corresponding color data such that the colored illumination bundles  112 ′,  114 ′, and  116 ′ are selectively passed on, in desired portions, as image bearing light. The portions of the illumination bundles  112 ′,  114 ′, and  116 ′ that are passed on as image bearing light may then coalesce into a colored image upon display.  
         [0026]     The optical assembly  108  may also include components adapted to process the illumination bundles  112 ,  114 , and  116  so that the transmitted illumination bundles  112 ′,  114 ′, and  116 ′ complement characteristics of the subpixels  124 ,  126 , and  128 . In one embodiment, the illumination bundles  112 ′,  114 ′, and  116 ′ may provide complementary illumination by being presented to the subpixels  124 ,  126 , and  128  in a manner to increase the overall light transmission through the respective subpixels  124 ,  126 , and  128 . Providing complementary illumination in such a manner to the subpixels may increase the overall brightness, efficiency, and/or contrast of the optical architecture  100 .  
         [0027]     In one embodiment, the optical architecture  100  may also include a polarizing analyzer behind the pixel  120  (not shown) to filter out stray polarized light, thereby potentially enhancing the contrast of the displayed image. Analyzers and polarizing filters can also be placed in other locations of the optical architecture  100  as may be appropriate for a particular application or illumination module.  
         [0028]     In one embodiment the illumination module  104  may include a polychromatic light source such as a gaseous discharge lamp (e.g., high-pressure mercury, tungsten, halogen, or metal halide). In this embodiment, reflective color filters (e.g., a dichroic interference filter) or refractive based color separating devices (e.g., a prism) may be used to separate the light into the desired colors for presentation to the corresponding subpixel. In other embodiments, monochromatic solid-state light sources such as, for example, light-emitting diodes, may be used to produce light of the desired color.  
         [0029]      FIG. 2  illustrates a side view of a lens  204  that may be used to present angular color separated (ACS) illumination to the pixel  120 . The lens  204 , which may be included in the optical assembly  108 , may be designed such that illumination that is incident upon the lens  224  within predetermined ranges of incident angles are focused on specific areas of the pixel  120 . For example, in one embodiment illumination bundles that have incident angles within a range Θ R  may be subsequently focused on the subpixel  128 ; illumination bundles that have incident angles within a range Θ G  may be subsequently focused on the subpixel  126 ; and finally, illumination bundles that have incident angles within a range Θ B  may be subsequently focused on a third subpixel  124 . Therefore, in one embodiment red, green, and blue illumination bundles  216 ,  212 , and  208 , respectively, may be simultaneously focused on subpixels  128 ,  126 , and  124 , respectively, for selective transmission.  
         [0030]     In one embodiment, the lens  204  may be adapted to anamorphically illuminate the subpixels  124 ,  126 , and  128  in order to complement characteristics of the subpixels such as the angular transmission distribution and/or the aspect ratio of the subpixels.  FIG. 3  illustrates the subpixels  124 ,  126 , and  128  being anamorphically illuminated in accordance with an embodiment of the present invention. In this embodiment, each of the subpixels  124 ,  126 , and  128  may have a rectangular aspect ratio with an elongated dimension in, e.g., the horizontal direction. The incident illumination bundles  208 ,  212 , and  216  may be transmitted through the lens  204  and focused upon the subpixels  124 ,  126 , and  128 , respectively, with an elongated axis that complements the rectangular apertures. This may result in elliptical illumination areas  304 ,  308 , and  312  presenting a substantial portion of the illumination to the transmittable region of the respective subpixels.  
         [0031]     In one embodiment each of the subpixels  124 ,  126 , and  128  may have similar characteristics. However, in other embodiments the subpixels  124 ,  126 , and  128  may have different characteristics. In one embodiment, different subpixel characteristics may be designed to complement the spectral properties of the light that the particular subpixel is adapted to receive. For example, in one embodiment in order to achieve a desired color balance, more illumination of one color, e.g., green, may be required than from other colors, e.g., blue and red. In this embodiment, as illustrated in  FIG. 10 , a subpixel that is to receive a green illumination bundle, e.g., subpixel  1004 , may have a larger rectangular aspect ratio than the other subpixels, e.g., subpixels  1008  and  1012 , to allow for a greater portion of green illumination to be transmitted.  
         [0032]     The lens  204  may be one of an array of lenses that are arranged to illuminate a corresponding array of pixels. In various embodiments, the lenses and the pixels may have a one-to-one, a one-to-plurality, or a plurality-to-one correspondence. In one embodiment, the lens array may be an array of lenticular lens elements. In this embodiment, each of the lenticular lens elements may illuminate a corresponding row of pixels.  
         [0033]      FIG. 4  illustrates a light valve display  400  being illuminated in accordance with an embodiment of the present invention. In this embodiment, the light valve display  400  may have an array of light valve pixels  404 . Each light valve pixel  404  may have a number of selectively controlled subpixels, similar to the pixel  120  discussed above. In this embodiment, illumination bundles may be focused onto the display  400  through a lenticular lens array (not shown) with the resulting lenticular illumination  408  being striped across the face of the display  400 . The lenticular illumination  408  may include distinct illumination bundles  412 ,  416 , and  420  that are a result from the lenticular array being illuminated with ACS illumination, as discussed above. The distinct illumination bundles  412 ,  416 , and  420  may provide complementary illumination to the subpixels of the pixels  404 .  
         [0034]      FIG. 5  illustrates a side view of an optical architecture  500  with ACS illumination, in accordance with an embodiment of the present invention. In this embodiment, an illumination module may include solid-state light sources  504   R ,  504   G , and  504   B , such as light-emitting diodes, to produce illumination bundles of primary colors, e.g., red, green, and blue, respectively. In one embodiment collimating optics  508   R ,  508   G , and  508   B  may placed in each of the illumination paths to receive diverging illumination bundles from the light sources  504   R ,  504   G , and  504   B  and transmit illumination bundles that contain substantially parallel light rays. In various embodiments, the collimating optics  508   R ,  508   G , and  508   B  may include one or more collimating lenses.  
         [0035]     In one embodiment reflective polarizers  512   R ,  512   G , and  512   B  may be positioned in the various illumination paths to allow for light of one polarization state, e.g., P-polarization, to be transmitted while reflecting light of a substantially orthogonal polarization state, e.g., S-polarization. In other embodiments a converse arrangement and/or other polarization states may be used. The reflective polarizers  512   R ,  512   G , and  512   B  could include, but are not limited to, a wire-grid polarizer, a cholesteric polarizer, a polymer film stack, or a dielectric coating stack. The reflective polarizers  512   R ,  512   G , and  512   B  may each be a portion of a reflective polarizer or, alternatively, may be separate reflective polarizers.  
         [0036]     The transmitted polarized light may then illuminate a microlensed display  516  across a range of illumination angles. The microlensed display  516  may include an array of lenses optically coupled to a light valve display, as discussed above with reference to earlier embodiments.  
         [0037]     As described above, the reflective polarizers  512   R ,  512   G , and  512   B  may only allow P-polarized light to be transmitted so that the microlensed display  516  may properly manipulate the polarization of the light for selective transmission.  FIG. 6  illustrates a top view of an embodiment of the optical architecture  500  that may provide for the recycling of the S-polarized light. In this embodiment, the light-emitting device  504   G  may transmit an illumination bundle of randomly polarized light towards the reflective polarizer  512   G . The P-polarized portion of the illumination bundle may be transmitted through the reflective polarizer  512   G  and illuminate the microlensed display  516  along a primary optical path  604 .  
         [0038]     In this embodiment, S-polarized light may be reflected from the reflective polarizer  512   G  towards a recycling assembly  604   G . S-polarized light may be indicated in the figures by small circles in the light paths suggesting a polarization vector normal to the plane of the drawing sheet. The light-emitting device  504   G  may be non-orthogonal to the reflective polarizer  512   G  to facilitate an angled reflection.  
         [0039]     The recycling assembly  604   G , which may include a polarization rotation device and a reflecting device, may rotate the S-polarized illumination bundle to the P-polarization state and redirect it towards the reflective polarizer  512   G . In various embodiments, the polarization rotation device may be quarter-wave plate or a quarter-wave film on the reflecting device. The recycled illumination bundle with the rotated polarization state may then be transmitted through the reflective polarizer  512   G  and illuminate the microlensed display  516  along a recycling optical path  612 .  
         [0040]     Referring again to  FIG. 5 , in one embodiment the reflective polarizers  512  may be designed in a manner to reflect the S-polarized portions of the illumination bundles back towards the horizontal planes that the originating light sources are on. In this context, the horizontal plane may be a level plane normal to the plane of the drawing sheet. For example, the S-polarized portion of the illumination bundle originating from light-emitting device  504   G  may be reflected towards a recycling assembly  604   G  that is on the same horizontal plane as the light-emitting device  504   G . This may, in turn, facilitate the presentation of the recycled illumination within the desired range of incident angles at the microlensed display  516 .  
         [0041]      FIG. 7  illustrates a pixel  700  overlaid with illumination from the primary optical path  604  and the recycling optical path  612 , in accordance with an embodiment of the present invention. In this embodiment, the pixel  700  may have subpixels  704 ,  708 , and  712  similar to those of the pixel  120  discussed above. Each of the subpixels  704 ,  708 , and  712  may include primary hot spots  716  resulting from the illumination bundles impinging upon the pixel  700  along the primary optical paths  604  and recycled hot spots  720  resulting from the illumination bundles along the recycling optical paths  612 . Developing the optical architecture to present these illumination bundles in a side-by-side manner as shown may complement characteristics of subpixels such as the rectangular aspect ratio and/or angular transmission distribution.  
         [0042]     Although the above embodiment illustrates an optical architecture producing two, substantially elliptical, illumination bundles incident upon the light valve pixel, other embodiments may not be so limited. For example, other embodiments may include three illumination bundles presented to the subpixel side-by-side-by-side, in order to take advantage of the geometrical transmissivity properties of the subpixel.  
         [0043]      FIG. 8  illustrates an optical architecture  800  employing a recycling assembly  804  in accordance with another embodiment of the present invention. For simplicity,  FIG. 8  illustrates only the polarization states along the optical paths of the optical architecture  800  and not the light rays. In this embodiment, illumination bundles may travel from the light-emitting device  504   G , through the collimating lens  508   G , and be incident upon the reflective polarizer  512   G , in a manner similar to the embodiment depicted and discussed with reference to  FIG. 6 . However, in the present embodiment, the S-polarized portion may be reflected towards a reflective device  808 . The reflective device  808  may redirect the S-polarized portion through a polarization rotation device  812 , e.g., a half-wave plate or film. The polarization rotation device  812  may rotate the S-polarized light to the P-polarization state and transmit the light to the microlensed display  516 .  
         [0044]      FIG. 9  is a simplified pictorial plan view of a system including a video unit  904  coupled to a projection device  908 , in accordance with an embodiment of the present invention. In this embodiment the video unit  904  may transmit video signals to the projection device  908 , which may include an illumination module  912  optically coupled to an optical assembly  916 . The optical assembly  916  may provide light to a light modulator  920  that may in turn present image bearing light to projection optics  924 . The components of the projection device  908  may cooperate with one another to jointly effectuate rendering of desired images, which may be image frames of a video, based on the transmitted video signals.  
         [0045]     The video unit  904  may include a personal or laptop computer, digital versatile disk (DVD), set-top box (STB), video camera, video recorder, an integrated television tuner, or any other suitable device to transmit video signals to the projection device  908 . In various embodiments, the system may be, for example, a projector or a projection television.  
         [0046]     In one embodiment, the light modulator  920  may be, e.g., a liquid crystal light valve. Examples of these types of light valves include, but are not limited to reflective displays such as LCoS (Liquid Crystal on Silicon) as well as transmissive displays, such as thin film transistor (TFT), polysilicon (P—Si), and Silicon-on-Insulator (SOI). In one embodiment, the light modulator  920  may include a liquid crystal display that may include a number of individually controllable subpixels similar to the pixels  120  or  700  described in reference to earlier embodiments.  
         [0047]     The optical assembly  916  may include an array of lenses optically coupled to the array of pixels of the light modulator  920 . The optical assembly  916  may also include optics adapted to present the primary colored light to the lens array along three ranges of incident angles. The lens array may then focus the primary colors onto the subpixels being controlled with the corresponding primary colored image data based on the transmitted video signals.  
         [0048]     Importantly, while embodiments of the present invention are described with reference to a video projector, the embodiments discussed herein are equally applicable to any type of illumination system for a polarization-based display, whether for projection or direct viewing, whether compact or not. For example, the techniques described herein are thought to be useful in connection with computer and data device displays, television and movie projectors, internet appliance viewers, and entertainment systems for video and game players.  
         [0049]     Although specific embodiments have been illustrated and described herein for purposes of description of the preferred embodiment, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent implementations calculated to achieve the same purposes may be substituted for the specific embodiment shown and described without departing from the scope of the present invention. Those with skill in the art will readily appreciate that the present invention may be implemented in a very wide variety of embodiments. This application is intended to cover any adaptations or variations of the embodiments discussed herein. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.