Abstract:
A microelectrical mechanical system (MEMS) optical raster display system includes a microelectrical mechanical system (MEMS) device that supports a reflective surface and tilts it in first and second transverse directions. The reflective surface is positioned to receive modulated light from a light source and to direct reflected light toward an image surface, such as a display screen, in a raster scan pattern. The raster scanning of the light is coordinated with the modulation of the light to form a display image on the display screen. In one implementation, the system includes multiple modulated light sources that each direct modulated light toward the reflective surface. The light sources are positioned so that the reflective surface reflects modulated light from each light source to a separate region of the display screen, thereby forming plural contiguous, generally non-overlapping, raster scan patterns.

Description:
TECHNICAL FIELD 
   The present invention relates to optical display systems and, in particular, to a microelectrical mechanical system (MEMS) optical raster display system. 
   BACKGROUND AND SUMMARY 
   Raster scanning is a long-standing display technique in which a beam is scanned across a display screen to impart a display image. Conventionally, an electron beam in a cathode-ray tube is scanned across a phosphor screen, as in standard television sets and computer display monitors. The pixels of an image are rendered sequentially as the electron beam is scanned across the display screen. 
   Development has since emphasized various pixelated panel displays in which a panel is formed with multiple pixels, as in a liquid crystal cell. The multiple pixels, or significant groups of the multiple pixels, are rendered substantially simultaneously rather than completely sequentially as in a raster display. Various liquid crystal technologies have been developed. Recently an integrated circuit pixelated reflective display has been developed and is called the digital micromirror device, which is available from Texas Instruments Incorporated. 
   As is known in the art, the digital micromirror device includes an array of micromechanical mirrors that are formed as part of a structure that is manufactured in accordance with integrated circuit manufacturing processes. Each micromechanical mirror corresponds to one pixel in the display. The digital micromirror device imparts display information on light by controllably tipping each of the micromechanical mirrors to control the amount of light that is reflected from the mirror to a display screen. 
   With the increasing sophistication and cost of pixelated panel displays, interest has returned to raster scanning. But rather than being used within a cathode ray tube, optical displays are being developed to use raster scanning of a light beam over a display screen. The display screen may be reflective, transparent, or translucent, according to the relative positioning of the light source and the viewer or viewers. The light intensity is modulated in coordination with the raster-scanning of the light beam to impart a display image over the surface of the display screen. 
   In some instances, microelectrical mechanical system (MEMS) actuators have been applied to raster scanning of light to form an optical display. MEMS actuators provide control of very small components that are formed on semiconductor substrates by conventional semiconductor (e.g., CMOS) fabrication processes. MEMS systems and actuators are sometimes referred to as micromachined systems-on-a-chip. 
   Examples of such actuators are described in U.S. Pat. No. 6,422,011 for Thermal Out-of-Plane Buckle Beam Actuator and US Patent Application Publication No. 2002-0088224 for Resonant Thermal Out-of-Plane Buckle-Beam Actuator, both assigned to Microsoft Corporation. In these examples, one or more MEMS actuators support one or more mirrors that controllably reflect light to form a raster scan on a display screen. The intensity of the light source is modulated and the micromechanical device functions to raster scan the modulated light over the display. 
   An aspect of the present invention is an appreciation that raster scanning of a display by a relatively small-scale MEMS device can be constrained by structural limitations of the MEMS device, thereby limiting the scope and range of the raster scan pattern. In a pixelated reflective display such as is provided by digital micromirror devices, the limited motion of the micromechanical devices is adequate to impart the modulation of the light intensity of a single pixel. 
   The present invention includes, therefore, a microelectrical mechanical system (MEMS) optical raster display system. The system includes a microelectrical mechanical system (MEMS) device that supports a reflective surface and tilts it in first and second transverse directions. The reflective surface is positioned to receive modulated light from a light source and to direct reflected light toward an image surface, such as a display screen, in a raster scan pattern. The raster scanning of the light is coordinated with the modulation of the light to form a display image on the display screen. 
   In one implementation, the system includes multiple modulated light sources that each direct modulated light toward the reflective surface. The light sources are positioned so that the reflective surface reflects modulated light from each light source to a separate region of the display screen, thereby forming plural contiguous, generally non-overlapping, raster scan patterns. 
   The raster scanning of multiple light beams allows one reflective surface and MEMS device to render a larger display area than could be rendered with only one light beam. As a result, the cost of implementing such an optical raster display is correspondingly reduced. 
   Additional objects and advantages of the present invention will be apparent from the detailed description of the preferred embodiment thereof, which proceeds with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagrammatic illustration of a microelectrical mechanical system (MEMS) raster optical display system operated with a single light beam. 
       FIG. 2  is a diagrammatic illustration of multiple microelectrical mechanical system (MEMS) raster optical display systems forming adjacent raster scan patterns. 
       FIG. 3  is a diagrammatic illustration of a microelectrical mechanical system (MEMS) raster optical display system operated with multiple light beams to form adjacent raster scan patterns. 
       FIG. 4  is a diagrammatic illustration of multiple microelectrical mechanical system (MEMS) raster optical display systems operated with multiple light beams to form adjacent raster scan patterns. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1  is a diagrammatic illustration of microelectrical mechanical system (MEMS) optical raster display system  10  having a reflective surface  12  on a MEMS device  14 . Illumination light  16  from a light source  18  is directed toward reflective surface  12 . MEMS device  14  tilts, pivots, or oscillates reflective surface  12  in two transverse directions  20  and  22  to reflect illumination light  16  toward an image surface, such as a display screen  24 . 
   The pivoting or tilting in transverse directions  20  and  22  cooperates with positioning of light source  18  to direct light across display screen  24  in a raster scan pattern  26 . The light from light source is modulated, either by modulating light source  18  or by modulating the light with a separate light valve (not shown), to impart image information on the light. As a result, the raster scanning of the light over display screen  24 , together with the modulation of illumination light  16 , forms a display image on display screen  24 . 
   It will be appreciated that the display image may be formed on surfaces other than a display screen, such as on another optical surface (e.g., lens), an electronic surface (e.g., camera input), etc. This would allow the display image to be used in other applications, such as a projection display. In addition, display system  10  may provide scanning (e.g., two-dimensional) of illumination light  16  in patterns other than raster scan pattern  26 . 
   In one illustrative implementation, MEMS raster display system  10  is capable of imparting to reflective surface  12  a tilt or pivot of about 3 degrees (i.e., +1.5 degrees) in each of transverse directions  20  and  22 . As a result, the effective scan angle is doubled to about 6 degrees upon reflection of illumination light  16 . Transverse directions  20  and  22  may correspond to the respective horizontal (x) and vertical (y) components of raster scan pattern  26 , for example. 
   With a scan range of 6 degrees in each direction  20  and  22 , light may be reflected from reflective surface  12  over scan space of about 36 square (solid) degrees, or about 0.1% of the available scan volume. For a conventional scan rate of 60 frames/second (i.e., 60 Hz in a slow-scan, or Y-direction), a fast scan rate of 3,000 Hz in an X-direction would provide for raster scan pattern  26  an array of 50×50 pixels. Such scan rates are compatible with available MEMS devices  14 . 
   Modulation of light source  18  in coordination with the raster scanning of illumination light  16  allows a 50×50 pixel display image to be imparted on display screen  24 . As another illustration, a display image of 100×100 pixels can be achieved with a maximum scan rate is 6,000 Hz or 6 KHz, which may also be achievable with some MEMS devices  14  with reflective surfaces  12 . 
   In one implementation, light source  18  may include a vertical cavity laser or “VCSELS,” which can provide low cost and high performance. These and other solid state light sources are capable of megahertz frequencies, as well as analog intensity control, thereby having sufficient bandwidth capabilities for adequate gray scales. 
   MEMS raster display system  10  illustrates use of a MEMS device  14  to provide raster scanning to form a display image. Limits on the angular extent at which some MEMS devices  14  can be tilted or pivoted can restrict the number of pixels that can be addressed at video rates (i.e., 60 Hz). One way to provide a display with pixel dimensions greater than can be provided by MEMS raster display system  10  alone is to employ an array  30  of MEMS raster display systems  10 , as illustrated in FIG.  2 . MEMS device  14  may be of any type that provides tilting or pivoting action at sufficient frequencies, such as the thermal actuators described in U.S. Pat. No. 6,422,011 or US Patent Application Publication No. 2002-0088224. 
     FIG. 2  is a diagrammatic illustration of multiple (e.g., four) microelectrical mechanical system (MEMS) optical raster display systems  10 A- 10 D that have reflective surfaces  12 A- 12 D on MEMS devices  14 A- 14 D, respectively. Illumination light  16 A- 16 D from light sources  18 A- 18 D is directed toward reflective surfaces  12 A- 12 D, respectively. MEMS devices  14 A- 14 D pivot or oscillate reflective surfaces  12 A- 12 D in respective transverse directions  20 A- 20 D and  22 A- 22 D to reflect illumination light  16 A- 16 D toward display screen regions  24 A- 24 D, respectively. The pivoting or oscillation in transverse directions  20  and  22  cooperate to direct light source  18  across display screen  26  in multiple raster scan patterns  28 A- 28 D. 
   Modulation of light sources  18 A- 18 D in coordination with the raster scanning of illumination lights  16 A- 16 D allows four 50×50 pixel raster scan patterns  28 A- 28 D to be imparted on display screen  26 . The raster-scanned image components are abutted or contiguous to provide a larger display (e.g., 200×200 pixels) than could be provided by a comparable MEMS raster display system  10  alone, as shown in FIG.  1 . 
     FIG. 3  is a diagrammatic illustration of a Raster Arrays of MEMS Optical Display Systems (RAMODS) implementation in which a microelectrical mechanical system (MEMS) raster display system  50  has a reflective surface  52  on a MEMS device  54 . Multiple illumination lights  56 A- 56 D from light sources  58 A- 58 D are directed toward reflective surfaces  52 . MEMS device  54  pivots, tilts, or oscillates reflective surfaces  52  in two transverse directions  60  and  62  to reflect illumination lights  56 A- 56 D toward display screen regions  64 A- 64 D, respectively. The pivoting or oscillation in transverse directions  60  and  62  cooperate to direct illumination lights  56 A- 56 D across display screen  66  in raster scan patterns  68 A- 68 D. 
   Modulation of light sources  58 A- 58 D in coordination with the raster scanning of illumination lights  56 A- 56 D allows four 50×50 pixel raster scan patterns  68 A- 68 D to be rendered on display screen  66 . The raster-scanned image components are abutted to or contiguous with each other to provide a larger display (e.g., 100×100 pixels) than could be provided by a comparable MEMS raster display system  10  employing only one light beam  16  (FIG.  1 ). 
     FIG. 4  is a diagrammatic illustration of a Raster Arrays of MEMS Optical Display Systems (RAMODS) implementation in which multiple microelectrical mechanical system (MEMS) raster display systems  50 A,  50 B have reflective surfaces  52 A,  52 B on MEMS devices  54 A,  54 B, respectively. Multiple illumination lights  56 A 1 - 56 A 4  and  56 B 1 - 56 B 4  from light sources  58 A 1 - 58 A 4  and  58 B 1 - 58 B 4  are directed toward reflective surfaces  52 A,  52 B. 
   MEMS devices  54 A,  54 B pivot, tilt, or oscillate reflective surfaces  52 A,  52 B in respective transverse directions  60 A,  60 B and  62 A,  62 B to reflect illumination lights  56 A 1 - 56 A 4  and  56 B 1 - 56 B 4  toward display regions  64 A 1 - 64 A 4  and  64 B 1 - 64 B 4 , respectively. The pivoting or oscillation in transverse directions  60 A,  60 B and  62 A,  62 B cooperate to direct lights  56 A 1 - 56 A 4  and  56 B 1 - 56 B 4  across display screen  66  in raster scan patterns  68 A 1 - 68 A 4  and  68 B 1 - 68 B 4 . 
   Modulation of light sources  58 A 1 - 58 A 4  and  58 B 1 - 58 B 4  in coordination with the raster scanning of illumination lights  56 A 1 - 56 A 4  and  56 B 1 ∫ 56 B 4  allows eight 50×50 pixel raster scan patterns  68 A 1 - 68 A 4  and  68 B 1 - 68 B 4  to be rendered on display screen  66 . The raster-scanned image components are displayed contiguously to provide a larger display (e.g., 100×100 pixels) than could be provided by a comparable MEMS raster display system  50  alone (FIG.  3 ). 
   It will be appreciated that arbitrary numbers of MEMS raster display systems  10  and  50  can be used together to form display images from arbitrary numbers raster scan patterns  26  and  68 . Likewise, the number of light sources  58  that can be directed to a reflective surface  52  of MEMS raster display system  50  is also arbitrary within practical limits. 
   Practical limits to the degree of multiplicity may based on a number of factors including the actual MEMS chip available, the scan angles and mirror sizes available to achieve the desired pixel count, the wavelength of light being used, etc. This invention, however, permits generating 4, 6 and even more rasters from a MEMS reflective surface (mirror) having even a limited scan angle, such as the 3 physical degrees discussed above. 
   Having described and illustrated the principles of our invention with reference to an illustrated embodiment, it will be recognized that the illustrated embodiment can be modified in arrangement and detail without departing from such principles. In view of the many possible embodiments to which the principles of our invention may be applied, it should be recognized that the detailed embodiments are illustrative only and should not be taken as limiting the scope of our invention. Rather, we claim as my invention all such embodiments as may come within the scope and spirit of the following claims and equivalents thereto.