Abstract:
A device for light processing includes a first housing having a reflective bottom surface and walls defining a first cavity. A first fluid or gel has a meniscus disposed within the first cavity. A control means is coupled with the first fluid or gel for adjusting the curvature of the meniscus. The bottom surface is configured to reflect an incident light beam through the first fluid or gel and toward the meniscus.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
   This application claims the priority to U.S. Provisional Patent Application No. 60/857,605, filed Nov. 7, 2006, which is hereby incorporated by reference in its entirety for all purposes. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to light processors and more specifically to digital light processors that eliminate the need for micro-mirror devices. 
   Space light modulators are transducers that modulate incident light in a spatial pattern corresponding to an electrical or optical input. The incident light may be modulated in its phase, intensity, polarization, or direction, and the light modulation may be achieved by using elements made of a variety of materials exhibiting various electro-optic or magneto-optic effects and by materials that modulate light by surface deformation. 
   Digital light processors (DLP) are light modulators suitable for various applications such as displays, projectors, televisions, monitors and printing. DLP devices use movable micro-mirrors to direct light into a projector lens, which focuses and magnifies the modulated light from each micro-mirror onto a display screen to produce an image. Since each micro-mirror represents a pixel of light or an image, a DLP device typically consists of a high density array of micro-mirrors on a single-chip integrated circuit. Each micro-mirror rotates about a fixed axis to cause light to be controllably deflected by the rotation. Thus, in some applications, an array of such micro-mirrors can be positioned so that the individual mirrors making up pixels are selectively rotated to create patterns for various purposes. 
     FIG. 1  shows two DLP cells with mirrors  100  and  102  on the top surface of each cell. Each mirror is attached to an underlying yoke that rotates on a torsion hinge, until the landing tips of the yoke contact the underlying landing pad sites. The micro-mirrors are tilted to reflect light onto and away from the projection screen, as desired. The tilting of the hinged mirrors as shown may be achieved by electro-static actuation. 
   However, one problem with conventional DLP devices is the problem of stuck mirrors, where the landing tips are slow to lift from the pads or become permanently stuck to the pads. This ‘sticking problem’ is an important consideration for reliable performance, since it is the most frequent cause of device failure. Sources of the sticking problem may include moisture in the package, scrubbing of landing tips onto the metal landing pads, and outgassing of the epoxy sealants used in the manufacturing process for mounting the devices in their packages. 
   Solutions to the sticking problem have included applying lubrication or a passivation layer to the metal surfaces, using resonant reset methods to pump energy into the pixel element to help free it from the surface, and adding gettering material to absorb moisture within the package. More recently, ‘spring-tips’ have been added to the tips of the mirrors. U.S. Pat. No. 6,583,921 addresses the problem by using a non-contacting hinge geometry that eliminates physical contact between the mirrors and the landing pads. 
   However, the above solutions fail to address other problems. For example, the hinge itself may become damaged or defective. Moreover, some of the above solutions suffer from long-term degradation of the passivant, which could drive the technology to require hermetic packages and complex process steps. Other problems that remain unaddressed include heating of the chip and difficult thermal management of the micro-mirrors, which must be cooled. An additional problem is the “pixel effect” or background noise characterized by stray points of light appearing on the display screen. The pixel effect may typically be reduced by blurring the image so that the pixels surrounding the noise pixels are blended. 
   Thus, it is desirable to provide systems and methods that overcome the above and other problems. In particular, there is a need for a DLP device that eliminates problems such as stuck mirrors and the pixel effect, while minimizing processing complexity and fabrication steps. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention provides a fluid or gel-based light processing system that overcomes the above problems. In particular, the present invention provides methods and systems for digital light processing for TVs, projectors, and other displays that eliminates the use of mechanical micro-mirrors. 
   According to one embodiment of the invention, a device for light processing includes a first housing having a reflective bottom surface and walls defining a first cavity. A first fluid or gel has a meniscus disposed within the first cavity. A control means is coupled with the first fluid or gel for adjusting the curvature of the meniscus. The bottom surface is configured to reflect an incident light beam through the first fluid or gel and toward the meniscus. 
   In one aspect, adjusting the curvature to above a critical curvature causes the meniscus of the first fluid or gel to deflect the reflected incident light to the bottom surface or the side walls of the cavity. 
   In another aspect, adjusting the curvature to below a critical curvature allows the reflected incident light to refract onto a surface outside of the housing. 
   According to another embodiment of the invention, a device includes a plurality of cavities, each having a reflective bottom surface. A fluid or gel having a meniscus is disposed within each cavity. A control means is coupled with the fluid or gel for adjusting the curvature of the meniscus disposed within each cavity, wherein the bottom surface is configured to reflect an incident light beam through the fluid or gel and onto an outside surface. 
   In one aspect, the plurality of cavities is provided by porous silicon. 
   In another aspect, the plurality of cavities is coupled with a multi-channel structure that is further coupled with a fluid or gel reservoir. 
   According to another embodiment of the invention, a method of manipulating light includes providing a fluid or gel within a housing that includes a bottom surface and a cavity, wherein the fluid or gel forms a meniscus disposed within the cavity. An incident light beam is focused to the bottom surface of the cavity, wherein the light beam reflects from the bottom surface to the meniscus. The curvature of the meniscus is adjusted so that the light refracts out of the cavity or reflects into the cavity. 
   In one aspect, the curvature of the meniscus is adjusted so that light refracting out of the cavity occurs when the curvature remains below a critical curvature. 
   In another aspect, the curvature of the meniscus is adjusted so that light deflecting into the cavity occurs when the curvature exceeds a critical curvature, wherein the incident light beam forms an incident angle that is larger than a critical angle for total internal reflection. 
   According to another embodiment of the invention, a method of manipulating light in a light processor without movable mirrors includes providing a fluid or gel within a housing that includes a reflective bottom surface and a cavity, wherein the fluid or gel forms a meniscus disposed within the cavity. An incident light beam is focused to the bottom surface of the cavity. The curvature of the meniscus is adjusted to manipulate the reflection of incident light. 
   In one aspect, adjusting includes adjusting the curvature of the meniscus to remain below a critical curvature so that a pixel of light turns on. 
   In another aspect, adjusting includes adjusting the curvature of the meniscus to exceed a critical curvature so that a pixel of light turns off. 
   According to another embodiment of the invention, a device for light processing includes a first housing having a reflective bottom surface and walls defining a first cavity. A first electro-active or conductive material has a meniscus disposed within the first cavity. A control means is coupled with the first electro-active or conductive material for adjusting the curvature of the meniscus. The bottom surface is configured to reflect an incident light beam through the first electro-active material and toward the meniscus. 
   In one aspect, the electro-active or conductive material is a fluid. 
   In another aspect, the electro-active or conductive material is a gel. 
   In another aspect, the curvature of the meniscus is adjusted by changing a contact angle formed by the electro-active or conductive material with the dielectric material on the walls of the cavity. 
   According to another embodiment of the invention, a light processor uses total internal reflection of light to control transmission, refraction or reflection of light. 
   According to another embodiment of the invention, a light processor uses total internal reflection and/or refraction and/or reflection of light to control the transmission, refraction or reflection of light in a device. 
   Reference to the remaining portions of the specification, including the drawings and claims, will realize other features and advantages of the present invention. Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with respect to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  shows two DLP cells with the left pixel turned on and the right pixel turned off. 
       FIG. 1B  shows two DLP cells with the left pixel turned off and the right pixel turned on. 
       FIG. 2  shows a cross section of a liquid or gel-based DLP device according to an embodiment of the invention. 
       FIG. 3  shows a simplified cross section of a liquid or gel-based DLP with a light beam projected onto a screen with the liquid or gel-based pixel in the “on” position, according to an embodiment of the invention. 
       FIG. 4  shows a simplified cross section of a liquid or gel-based DLP with a light beam not being projected onto a screen with the liquid or gel-based pixel in the “off” position, according to an embodiment of the invention. 
       FIG. 5  shows an array of micro cavities to be used for fabrication of liquid or gel-based DLP pixel array according to an embodiment of the invention. 
       FIG. 6A  shows a liquid or gel-based DLP pixel setup according to an embodiment of the invention. 
       FIG. 6B  shows a liquid or gel-based DLP pixel setup with a pixel turned on. 
       FIG. 6C  shows a liquid or gel-based DLP pixel setup with a pixel turned off. 
       FIG. 7  shows a liquid or gel-based DLP system according to an embodiment of the invention. 
       FIG. 8  shows a liquid or gel-based DLP system according to another embodiment of the invention. 
       FIG. 9  shows a liquid or gel-based DLP system according to another embodiment of the invention. 
       FIG. 10  shows a liquid or gel-based DLP system according to another embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A source of light directed at a conventional DLP array is typically reflected in one of two directions for each micro-mirror, or pixel. In one direction, the pixel is “off” so that incident light directed upon the mirror will be deflected to a light absorber. In the other direction, the pixel is in the “on” position, so that light incident to that pixel will be reflected to a projector lens. The projector lens then focuses and magnifies the modulated light from the pixel onto a display screen, or to a photosensitive element of a printer. If each pixel of the array is in the “on” position for the case of a display, the displayed image will be an array of bright spots or areas. 
     FIGS. 1A and 1B  show two pixels of a conventional DLP chip in the “on” and “off” modes.  FIG. 1A  shows two DLP cells with the left pixel  100  turned on and the right pixel  102  turned off. Incident light  104  hits both pixels, but only left pixel  100  reflects back light  106  to a projector lens, while right pixel  102  remains dark. In contrast,  FIG. 1B  shows two DLP cells with left pixel  100  turned off and right pixel  102  turned on. Here, only right pixel  102  reflects incident light  104  as reflected light  108 . Each micro-mirror, or pixel, of the conventional DLP array is individually controlled in such a way to either reflect incident light onto the projector lens or to deflect it to the light absorber. 
     FIG. 2  shows an exemplary embodiment of the invention. The embodiment shown in  FIG. 1  utilized the geometry of each micro-mirror to reflect or deflect light. However, the device shown in  FIG. 2  eliminates the use of mirrors completely, and uses instead a cavity  202  that is partially filled with a liquid or gel  204  (i.e., one or more droplets). The liquid may be water or any other suitable fluid. The gel may be an elastomer or other polymer or monomer blends. In other embodiments, the liquid or gel  204  may be replaced by any suitable electro-active or conductive material that is not limited to liquids or gels. Thus, instead of relying on mechanical parts, the resulting system is a liquid or gel-based DLP system (L/G-DLP) and uses the occurrence of ‘total internal reflection’ of incident light beam  200  to control and manipulate light, as discussed further below. 
   In one aspect, the top of cavity  202  is sealed with a transparent cover  212 , preferably having a non-reflective coating, so that incident light  200  may pass through the cover and liquid or gel  204 . Non-reflective coatings include various thin films or spin-on coatings. In one aspect, the bottom of micro-cavity  202  includes a highly reflective substrate  216 , so that incident light  200  may be reflected to the display screen from the device when in the “on” position. Reflective substrates can include substrates coated by reflective thin films such as silver, aluminum, etc. Part of cavity  202  is coated with a hydrophobic material  214 . The boundary at the hydrophobic regions constrains the liquid or gel and presents a meniscus having a curvature defined in part by the contact angle at the boundary. The hydrophobic material may be a material such as plastic, polymers, ceramics, alloys, or a fluoropolymer such as Teflon, CYTOP or zirconium oxynitride. In one aspect, the DLP system also includes a micro-via  208  and a piezoelectric diaphragm  218  to control the curvature of the lens and the reflection of light. An air gap  210  lies between the top cover  212  and liquid or gel  204 . 
     FIGS. 3 and 4  show incident light beams for the liquid or gel-based DLP system of  FIG. 2  in the two possible positions described. A beam of light is focused at the liquid/gel pixel or lens mirror in such a way to fulfill one of two criteria that determines whether the pixel is in the “on” or “off” position. For the “on” position, as shown in  FIG. 3 , the angle i 2  is less than a critical angle C, and for the “off” position as shown in  FIG. 4 , the angle i 4  is greater than the critical angle C. 
     FIG. 3  shows light beam  300  projected onto a projection screen  312  with the pixel in the “on” position. The angle i 2  is less than the critical angle C when the liquid or gel meniscus of the L/G-DLP pixel has a minimum curvature. When incident light beam  300  enters the L/G-DLP cavity  308  filled with a liquid or a gel, the light beam is refracted to follow path  302  in the liquid or gel. When the light beam hits the bottom reflective surface  310 , it is then reflected onto path  304 , and refracted outside the liquid or gel onto path  306  until it hits projection screen  312 . 
   In contrast,  FIG. 4  shows a light beam prevented from being projected onto a screen, with the pixel in the “off” position.  FIG. 4  shows that the angle i 4  is greater than the critical angle C when the meniscus of the liquid/gel pixel has a large curvature, or is concave. In this case, when incident light beam  400  passes into liquid/gel cavity  408  filled with a liquid or a gel, the beam is refracted into the path  402 . When the beam hits the bottom reflective surface  410 , it is reflected onto path  404 . In this case, however, the beam is deflected back into cavity  408  on path  406 , thus prevented from being projected onto projection screen  412 . The deflection occurs as a result of the curvature of the liquid or gel meniscus and is due to ‘total internal reflection.’ As shown in  FIG. 4 , a large enough curvature in the meniscus would change the angle of incidence of the reflected beam  404  sufficiently so that the angle of incidence on the meniscus is greater than the critical angle (i 4 &gt;C). Thus, light is reflected back at the meniscus (i.e., gas-liquid or gas-gel interface) after a minimum curvature of the meniscus is exceeded. 
   The radius of curvature of the liquid or gel meniscus thus forms the optics of the L/G-DLP pixel. Changes in the curvature of the liquid or gel meniscus from flat to concave may be caused by the use of an actuator, such as a piezoelectric actuator, artificial muscle, or shape memory actuator. Other actuating means include a voice coil pump, piezoelectric pump, motor-drive pump, mechanical pump, electrical pump, electro-mechanical pump, or any other suitable actuator or pump as known in the art. Since the actuating means causes shifts in the curvature of the meniscus that determine the occurrence of ‘total internal reflection’ of light, it thus controls the “on” or “off” positions of each pixel. 
     FIG. 5  shows another embodiment of a device according to the invention. In the device of  FIG. 5 , the pixels are formed by allowing coherent porous silicon, or another suitable porous material, to provide an array of cavities  500 . The use of coherent porous silicon enables the fabrication of very small pixels (i.e., 5 μm in diameter) as well as large pixels, depending on the application. 
     FIGS. 6A-6C  show a single pixel being turned on and off in an experimental setup of an embodiment of the invention.  FIG. 6A  shows the setup including a projection screen  600 , a substrate  602 , which includes a single L/G DLP-pixel and a light source  604 .  FIG. 6B  shows a light beam originating from the light source (not shown) reflecting light from cavity  606  into spot  608  on projection screen  600 , when the pixel is turned “on.”  FIG. 6C  in contrast shows the pixel in the “off” position. As in  FIG. 6B , an incident light beam is directed at the liquid/gel-based DLP at  606 . However, unlike in  FIG. 6B , the light beam is not reflected onto projection screen  600  due to the occurrence of ‘total internal reflection’ at the interface of gas-liquid or gas-gel, in the L/G-DLP pixel. 
     FIG. 7  shows a L/G-DLP system according to another embodiment of the invention. As described above, beam  700  enters liquid or gel  708  and is focused onto the reflective surface  710 . The beam is reflected to the display screen  712  on path  706  when the L/G-DLP is in the “on” position. In one aspect, liquid or gel  708  is conductive and in contact with power source  716  and conductive electrode  718 . Liquid or gel  708  may include any suitable conductive material not limited to liquids or gels. Application of a voltage from power source  716  will change the shape of the meniscus and thus change the value of i 4 , which determines the refraction or ‘total internal reflection’ of the light beam. The hydrophobic regions that constrain the conductive liquid or gel to provide for the meniscus are dielectric coatings  714 . 
     FIG. 8  shows an L/G-DLP system according to another embodiment of the invention that includes a conductive liquid or gel  808 . As for the embodiment above, a conductive electrode  818  is coupled with a power source  816 . A second conductive electrode may be provided, as shown by electrode  820  in  FIG. 8 . Alternatively, as shown in  FIG. 7 , the reflective surface  810  may also be used as a second electrode.  FIG. 8  also shows dielectric coatings  814  that provide for hydrophobic regions to constrain the conductive liquid or gel. The applied voltage from power source  816  may be AC or DC depending on the application to change the shape of meniscus  822 . 
     FIG. 9  shows an L/G-DLP system according to another embodiment of the invention. As for the embodiments above, light beam  900  is focused onto reflective surface  910  and reflected onto path  906  until it hits display screen  912  when the L/G-DLP is in the “on” position. The L/G-DLP system includes an actuating means  924 , which pumps liquid or gel  908  into the cavity of the L/G-DLP as shown. Actuating means  924  may include any of the various actuators or pumps as noted above, to change the curvature of the meniscus  911  of liquid/gel  908 . 
     FIG. 10  shows an L/G-DLP system according to another embodiment of the invention. Incident light beam  1000  is focused onto a reflective surface or coating  1014 . Unlike the embodiments described above, instead of changing the curvature of a meniscus to change the direction of an incident beam, reflective surface or coating  1014  is itself adjusted to be made concave or convex. In particular, reflective surface or coating  1014  may be positioned in housing  1010  with gel or fluid  1008 , so that the incident light beam  1000  is reflected onto screen  1012 . When reflective surface or coating  1014  is made convex as shown in  1016 , incident light beam  1000  is reflected away from screen  1012 , as indicated by beam  1002 . Likewise, when reflective surface or coating  1014  is made concave as shown in  1018 , incident light beam  1000  is also reflected away from screen  1012 , as indicated by beam  1004 . The curvature of reflective surface or coating  1014  may be changed by means of electro-wetting, actuation, or any other means that enable the incident light beam to be reflected in a direction away from screen  1012 . 
   Since the embodiments described above use the phenomenon of ‘total internal reflection’ or ‘refraction’ or ‘reflection’ to control and manipulate light, the need for movable micro-mirrors is eliminated. Several advantages are realized by this. For example, eliminating mechanical parts automatically eliminates significant causes of performance failure in DLP chips, such as stuck mirrors and damaged hinges for rotating the micro-mirrors. 
   Another improvement provided by L/G-DLP devices over conventional micro-mirror arrays is the elimination or minimization of the pixel effect. By manipulating the curvature of the liquid or gel meniscus, the stray spots of light could be made to smear on the projection screen, and produce a smoother picture and improve the overall picture quality. 
   Yet another advantage provided by L/G-DLP devices is the improved facility of thermal management. Since there are no pivoted components in embodiments of the invention, thermal conduction throughout the chip is improved by the use of liquid or gel cooling, instead of air cooling as for devices with arrays of movable micro-mirrors. 
   Moreover, since a lesser number of fabrication steps is required for the L/G-DLP system, the required fabrication process is simpler. Accordingly, a higher yield is expected, with lower production costs for the batch fabrication process. Additionally, automation in processing is increased since the liquid/gel-based digital processing system reduces the amount of hand-processed steps. 
   While the invention has been described by way of example and in terms of the specific embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements as would be apparent to those skilled in the art. For example, various possible arrangements of L/G-DLP pixel arrays exist and the embodiments are not limited to the ones described herein. Moreover, those skilled in the art will appreciate that the same techniques can apply to other types of fluids and materials, or other types of devices such as analog light processors. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.