Abstract:
The present invention provides a transmissive Spatial Light Modulator with fast response speed and higher brightness using micro-windows having switching transistors on said window so that the fill factor of light transferring area can be maximized. Conventional systems have transistors out of windows which substantially reduce the area to pass incoming light, because transistors are usually opaque and block light transmission. Transmissive Spatial Light Modulator requires simpler and smaller optics than reflective Spatial Light Modulator.

Description:
PRIORITY OF APPLICATION 
     This Patent Application is a Non-provisional Application and claims the Priority Date of a Provisional Application 61/404,617 filed on Oct. 6, 2010 by a common Inventor of this Application. The Disclosures made in the Patent Application 61/404,617 are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to an image display system that modulates illumination light from a light source and displays two-dimensional images. More particularly, this invention relates to an image display system implemented with a spatial light modulator which modulates incoming light by opening and closing micro-windows configured as a two dimensional pixel array. 
     After the dominance of cathode ray tube (CRT) technology in the display industry over the past 100 years, the Flat Panel Display (FPD) and Projection Display technologies are now gaining popularity because of a smaller form-factor of the display control system while projection and display of images of greater size onto a bigger display screen can be more conveniently performed. Among several types of projection display systems, projection display systems using micro-display are gaining consumers&#39; recognition because of high performance of picture quality as well as lower cost than the display systems implemented with FPDs. There are two types of micro-display technologies implemented in the projection display systems now made available in the market. The first type of display system is the micro-LCD (Liquid Crystal Display) system and the other type display system is the display system that implements the micromirror technology. The images displayed from a micromirror device have a significant advantage because of higher brightness by displaying the images by projecting an un-polarized light over the display image projected from a micro-LCD system, which uses polarized light. 
     More specifically, the electromechanical mirror device is drawing a considerable interest as a spatial light modulator (SLM). Micromirror devices have substantial advantages over LCD systems, because they do not use polarized light as LCD and creating polarized light causes substantial loss of incoming light nearly 50%. Furthermore, the micromirror devices also have substantial faster response time than LCD and this faster speed enables Color Sequential Control, meaning using a single device and alternating colors as fast as viewers do not recognize the change of colors. 
     Additionally, due to the slow speed, the LCD image projection systems typically are required to implement three panels and do not allow for Color Sequential Control. Compared with systems implemented with three panels, the image display systems implemented with a single panel has significant cost advantages of providing with device with a much lower cost than the three panel systems. 
     Even though the micromirror devices have significant advantages over the LCD systems, the optics systems are usually more complicated because of reflection systems rather than transmissive systems. Reflective optical systems often require larger sizes than transmissive optical system. The advantages and cost benefits of the micromirror devices are adversely affected due to this requirement of a larger optical system when the reflective optical configuration is implemented. In addition to the requirement of optics of larger size, the reflective display devices are further limited to application in the projection display apparatuses while the transmissive display systems have broader applications for implementation in the direct view and projection display systems, such as the LCD display systems. 
     U.S. Pat. Nos. 7,417,782 and 7,460,290 disclose MEMS Shutters such as that shown in  FIG. 15A , with shutters employ the sliding shutter to open and shut off a shutter manufactured by the MEMS technology. However, such systems are limited by the fact that the structure cannot have more than 50% of opening due to its sliding door type structure. In contrast, the Micro-windows can achieve higher brightness and are more desirable because the micro-windows have higher opening ratio. 
     The technical article, “Magneto-structural Simulation of a MEMS Micro-shutter” by Abed M. Khaskia published at FEMCI Workshop/NASA GSFC on Jun. 15, 2004, shows that micro-shutter with torsion hinge actuated by magnetic force. However, this structure as that shown in  FIG. 15B , requires high power to drive. 
     Therefore, a need still exists in the art of image display projection systems. More particularly in the micromirror device display system to provide a new and improved optical configuration and design methods to simplify the optical transmission configurations and reduce the size of the spatial light modulator (SLM) such that the difficulties and limitations as now encountered by those of ordinary skill in the art can be resolved. Another need exists to improve the brightness and resolution of direct view LCD display systems whose light utilization is below 10% and requires three color dots in a pixel. 
     SUMMARY OF THE PREFERRED EMBODIMENTS 
     Therefore, one aspect of this invention is to disclose a new image display system with fast and bright transmissive display configuration to enable a display system implemented with a single device Color Sequential Control. The image display system has simpler optics and more compact size thus providing a more cost effective apparatus while achieving higher performance by displaying images with improved quality. 
     Specifically, it is an aspect of this invention that provides a new image display system with fast and bright transmissive display configuration by making and using movable micro-windows to operate in an open or close state for modulating and controlling the pixels to display color images with high speed control while reducing the overall size of the optical system. 
     While the novel features of the invention are set forth with particularly in the appended claims, the invention, both as to organization and content, will be better understood and appreciated, along with other objects and features thereof, from the following detailed description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 and 2  are a side view and a top view to illustrate the basic concepts of the micro-windows of this invention. 
         FIG. 3  is a side view of a mirror element for illustrating the structure and operation of the micro-window. 
         FIG. 4  is a side cross-section view of the micro-mirror element across a line A-A of  FIG. 3 . 
         FIG. 5  is a side view of a mirror element as another embodiment of this invention for illustrating the structure and operation of the micro-window. 
         FIG. 6  shows the side view for illustrating the structure of the mirror element of  FIG. 5  that uses torsion hinges. 
         FIG. 7  is a cross sectional view to illustrate an example of substrate to create micro-windows in this invention. 
         FIG. 8  is a cross sectional view for illustrating an embodiments of this invention using multiple layer substrate as to form FET (Field Effect Transistor) on the top layer. 
         FIG. 9  is a schematic diagram for illustrating an embodiment of the optics of micro-mirror with three light sources. 
         FIG. 10  is a schematic diagram for illustrating an embodiment of the micro-window wherein no total-internal-reflective prism is required. 
         FIG. 11  is a schematic diagram for illustrating a micro mirror optics, wherein the mirrors cause diffraction and diffracted light beams are reflected toward the projection lens. 
         FIG. 12  is a schematic diagram for illustrating a micro mirror optics, wherein the mirror is operated in an OFF position. 
         FIG. 13  shows an example of optics of micro-window, wherein outgoing light beams including diffracted beams are projected to the screen. 
         FIG. 14  shows the micro-window operated in an OFF position thus not passing any light to the projection lens nor to the screen. 
         FIGS. 15A and 15B  are perspective view and a side view respectively of two conventional display systems implemented with micro-shutter structures. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  and  FIG. 2  show a basic concept of micro-windows.  004  in  FIG. 4  is incoming light toward all pixels. Each of the pixels has a movable micro-window as  002  and  003 .  002  is a closed window which shut light off and  003  is a open window which allow incoming light to go through.  FIG. 2  shows an array of display using micro-windows.  005  is an open window and the pixel looks bright and  006  is a closed window and the pixel looks dark. 
       FIG. 3  shows an example of this imvention.  101  is a plate functioning as a micro-window, which moves with the hinges,  108 ,  109  and  110 . This example has 3 hinges made of cantilevers. The window,  101 , can move around the horizontal axis with the 3 hinges as a door.  102  is a stationary frame. The window,  101 , is driven with an electro-static force. A voltage is applied to the window from the bit-line  101  and the word-line  111  with a ground line of  112 . The output voltage of the transistor  103  will be outputted to  104 , which is connected to the plate  403  in  FIG. 8 . 
       FIG. 4  shows side view at the A-A′ line.  203  is a transparent substrate so that light can go through.  101  is the closed position of the window.  201  is a half open position and the window can go to the vertical position depending on the applied voltage.  102  is a side wall of a cavity in a pixel. The sidewalls are covered with a conductive coating,  202 , so that the surface is electrically ground. 
     To apply voltages to the window, 3 hinges are conductive and they are connected to the voltage supply lines shown as bit-line  101  and  114 , word-line  111  and ground line  109 . The plate forming the window has at least one transistor to select a pixel to apply the incoming voltage from the bit-line ( 101 ). Prior arts place a transistor out of windows. However it will reduce the size of windows, because transistors are usually opaque and do not allow light to pass through. This invention allows larger windows because a transistor is placed on a window. After voltage is applied to the capacitor  104 , which is also placed on the window, the capacitor will hold the voltage until the next signal writing. 
       FIG. 5  is another embodiment of this invention. This example uses two torsion hinges,  303  and  311 , to move the window,  304 , as well as supplying three voltages to the window. At least one of hinges has to have two layers to supplies two voltages. 
       FIG. 6  shows the side view of  FIG. 5  structure, which uses torsion hinges. The window  304  rotates around the hinges when voltage is applied to a conductive plate under the window  320  ( FIG. 6 ) or  403  ( FIG. 8 ). 
       FIG. 7  shows an example of substrate to create micro-windows in this invention.  401  is a substrate having a release layer  402 , light blocking opaque and electrically conductive layer  403 , insulating layer  404  and semiconductor layer  405 . This type of substrate having multi layers is available as double SOI (Silicon-On-Insulator). 
       FIG. 8  is an example of embodiments of this invention. Using multiple layer substrates as described in  FIG. 8 , FET (Field Effect Transistor) can be formed on the top layer  405 .  410  is a gate and  411  is a gate insulator layer.  408  and  414  are Drain and Source.  411  is the connector to the gate,  413  is the connector to the source and  415  is the connector to ground. The word-line voltage is applied to the gate and the video signal is applied to the source which will be passed to the via  406  and the opaque and conductive plate  403 . The plate  403  with the voltage will be attracted to the direction of the ground  202  in  FIG. 4  or  FIG. 6  by electro-static force. The release layer  402  can be etched off with suitable etchant and the layers above the release layer can be lifted off and transferred to a transparent substrate to form a micro-window display as described in  FIG. 1 ,  FIG. 2 ,  FIG. 4  and  FIG. 6 . 
       FIG. 9  shows an example of optics of micro-mirror wherein three light sources,  505 ,  506  and  507  are used for three different colors and a cross prism  508  is used to integrate said three colors into a same direction and a pair of prism forming total internal reflection (TIR) prism  502  directing incident light toward said micro-mirrors  501  and the reflected lights are projected to a screen  504 . 
       FIG. 10  shows an example of optics of micro-window  509  wherein no total-internal-reflective prism is required. Thus micro-window simplifies optics and reduces the size of system substantially. 
       FIG. 11  shows an example of micro mirror optics, wherein the mirrors cause diffraction and diffracted light beams are reflected toward the projection lens. When said micromirrors are at ON position, these diffracted light  609  beams from a single mirror are still focused into a single point on a screen  601  and this will not cause a problem. However when said mirror is at OFF position, the diffracted light beams  609  are projected into the lens and some of beams  609  are still projected to the screen. This means that OFF mirrors cannot become completely black, but they will stay as gray as in  FIG. 12 . As this, undesirable light leakage will take place, especially when laser beam is used as light source because laser has strong coherence and interference which scatters light reflected by periodical structures. This scattering is unavoidable when coherent light such as laser is used. 
       FIG. 13  shows an example of optics of micro-window, wherein outgoing light beams including diffracted beams are projected to the screen as well as micro-mirrors. However,  FIG. 14  shows that said micro-window at OFF position does not pass any light to the projection lens nor to the screen, where an OFF position makes complete black at the screen and the contrast will be perfect. Micro-window can avoid undesirable light at OFF position even a laser light source is used. This is a significant advantage of micro-window over reflective display devices. 
     The main advantage of this invention is substantially larger window than conventional systems; because a transistor requiring a large footprint is placed on a window rather than on a stationary place. 
     While specific embodiments of the invention have been illustrated and described herein, it is realized that other modifications and changes will occur to those skilled in the art. It is therefore to be understood that the appended claims are intended to cover all modifications and changes as fall within the true spirit and scope of the invention.