Patent Abstract:
An optically addressed spatial light modulator may be formed with an integrated light emitting device display. The light emitting device display may be formed of a size and cost that optimizes the overall modulator design. In addition, by integrating the modulator and display devices, the overall size of the spatial light modulator may be reduced in some embodiments.

Full Description:
BACKGROUND  
         [0001]    This invention relates generally to optical systems and elements and more specifically to optically addressable spatial light modulators or light valves.  
           [0002]    A spatial light modulator is a class of optical device used for optical computation, switching and displays. A liquid crystal display is one type of spatial light modulator. The liquid crystal display is a two-dimensional spatial light modulator where the physical orientation, and hence magnitude of optical rotation, of a liquid crystal (LC) is modulated by an electric field. In combination with other polarizers in the light path, the intensity of light transmitted through the LC comprising element or light valve is modulated.  
           [0003]    Generally, a spatial light modulator includes a modulating write or addressing mechanism. Conventionally, in spatial light modulators, the addressing mechanism is fully electrical, for example, using an active matrix amorphous silicon array to select the voltage at a given pixel&#39;s electrode.  
           [0004]    However, optically addressed spatial light modulators are also known. In optically addressed spatial light modulators the voltage across the liquid crystal in the light valve is optically modulated by the exposure of the photoconductor layer to a write beam signal. The write beam is developed externally to the liquid crystal comprising element.  
           [0005]    Spatial light modulators also include a read or output mechanism that may be simply the visible observation of the transmitted and modulated light. For a reflective liquid crystal display, the source of light for readout is on the same side of the liquid crystal comprising element. The write mechanism involves a read beam passing through the front side of the liquid crystal comprising element and being reflected back through the front side.  
           [0006]    The optically addressed spatial light modulators tend to be bulky. The use of an external write beam takes up excessive space and necessitates optical alignment. Also the optically addressed partial light modulators tend to be expensive and mechanically awkward. Generally, light emitting device arrays are utilized to generate the write beam. These arrays are relatively expensive and not generally monolithic, but rather they are assemblages of large discrete devices.  
           [0007]    Thus, there is a need for better ways to implement optically addressed spatial light modulators. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is an enlarged cross-sectional view of one embodiment of the present invention;  
         [0009]    [0009]FIG. 2 is an enlarged cross-sectional depiction of another embodiment of the present invention;  
         [0010]    [0010]FIG. 3 is an enlarged cross-sectional view of still another embodiment of the present invention;  
         [0011]    [0011]FIG. 4 is an enlarged cross-sectional view of but another embodiment of the present invention; and  
         [0012]    [0012]FIG. 5 is an enlarged cross-sectional view of still another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0013]    Referring to FIG. 1, an optically addressed spatial light modulator  10  includes a light valve  12  that receives an external read beam as indicated. Integrated with the light valve  12  is an organic light emitting device (OLED) display  14 . The display  14  may include a substrate  16 , which in one embodiment may be a silicon integrated circuit. Organic light emitting devices  20  are formed on the surface of the substrate  16 . The devices  20  may comprise organic materials, such as conjugated polymer or small molecule-based light emitting materials. The organic material may comprise one or more layers. Each device  20  forms a subpixel of an OLED display.  
         [0014]    The devices  20  are covered by a passivation  18 . Examples of passivation materials include silicon oxide or silicon nitride deposited by sputtering or plasma-enhanced chemical vapor deposition.  
         [0015]    An index matching material  22  may be positioned between the passivation  18  and the light valve  12 . The display  14  may be sealed by a sealant  24 , such as epoxy. The sealant  24  and the passivation  18  together function to protect the devices  20  from the ambient since the deposits  20  may be subject to moisture and solvent damage.  
         [0016]    In one embodiment, a flexible circuit  26  may be utilized to supply signals to the substrate  16  and its integrated components. Thus, addressing signals may be provided through the flexible circuit  26  to a passive matrix addressing system. Alternatively, the pixel drive signals may be developed on chip in an active matrix addressing circuit. The light from the organic light emitting devices  20  develop the write beam so no external write beam is required although the read beam may still be external to the assembly as shown in FIG. 1.  
         [0017]    The index matching material  22  may have an index of refraction about equal to that of the substrate  16 . The material  22  may have adhesive properties that assist the sealant  24  in bonding the display  14  to the light valve  12 . In practice, small gaps may be left in the sealant  24  and the index matching material  22  may fill those gaps in one embodiment or an external sealant may be added to the gaps.  
         [0018]    When appropriate current is driven through each device  20 , it emits light. Generally, each device  20  may be sandwiched between a pair of spaced electrodes, one positioned between the device  20  and the substrate  16  and the other positioned on the opposite side that is substantially transparent. When current flows through a device  20 , the device  20  emits light in a direction away from the substrate  16  in one embodiment. This light then is utilized to optically address the light valve  12 .  
         [0019]    Referring next to FIG. 2, an optically addressed spatial light modulator  10   a  is similar to the modulator  10  shown in FIG. 1, except that the light developed by the device  20  is actually utilized as the read beam. Therefore, no external read beam may be required.  
         [0020]    Referring next to FIG. 3, the optically addressed spatial light modulator  10   b  incorporates a microlens  30 . The microlens  30  is formed on, or is attached to, the light valve  12   a  in one embodiment. Alternatively, the microlens  30  may be formed on the display  14 .  
         [0021]    The microlens  30  allows the light from the OLED display  14  to be controllably dispersed onto the light valve  12   a , increasing the perceived fill factor of the read beam by modulating a larger area of the light valve  12   a . This is particularly suitable for light valves  12   a  with continuous modulating material such as a photoconductor as opposed to light valves using PIN photodiodes. To facilitate light focusing, an air gap  31  may be left between the display  14  and the light valve  12   a  in one embodiment.  
         [0022]    Turning next to FIG. 4, a color filter  32  may be formed on or attached to the light valve  12   b . For example, the filter  32  may be a dielectric filter formed from inorganic materials such as alternating layers of silicon dioxide and titanium dioxide. As still another example, the filter  32  may be a color filter formed from dye containing organic materials. As still another alternative, the filter  32  may be formed on, or attached to, the display  14 . Again, an air gap  31  may be left between the filter  32  and the rest of the display  14 .  
         [0023]    The OLED display  14  spectrum can be chosen to range from blue to red and into the infrared range through the use of a filter  32  in some embodiments. Therefore, the light output can be reduced to a suitably narrow band, and the output light may be optimized for specific modulating elements without interfering with the read beam. For example, with certain amorphous silicon PIN diodes, 514 nm. wavelength light beams may be beneficial. Other very narrow spectrum light beams can also be developed using the displays  14 .  
         [0024]    Turning finally to FIG. 5, an optically addressable spatial light modulator  10   d  includes an OLED display  14   a  using a transparent substrate  16   a . The light developed by the OLED material devices  20  passes through the transparent substrate  16   a , through the microlens array  34 , through an air gap  31 , and finally through a filter  32  to the light valve  12 .  
         [0025]    A sealant  24  seals the region on the output side of the substrate  16   a . Similarly, a sealant  38  seals the region containing the devices  20 . In some embodiments, a filler  40  may be formed in the region defined inside the cover  36 . The filler  40  may include a dessicant in some embodiments. The passivation  18  may cover the device  20  in some embodiments.  
         [0026]    In still other embodiments, the OLED display  14  may be formed on the side of the substrate  16  adjacent the light valve  12 . Drive electronics (not shown) may be disposed on the other side of the substrate  16 . The substrate  16  may include a ceramic material such as alumina, with interconnecting vias coupling the OLED address lines to the drive electronics. See PCT patent application publication no. WO 99/41732 dated Aug. 19, 1999. As still another alternative, the OLED display  14  may be replaced with thin film electroluminescent (TFEL) devices, such as those sold by Planar Systems, Inc., 1400 NW Compton Drive, Beaverton, Oreg. 97006-1992, with either passive or active matrix addressing.  
         [0027]    While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.

Technology Classification (CPC): 6