Abstract:
Prism assemblies for projector display systems disclosed receive inputs from discrete color channels (e.g., red, green and blue channels. In one embodiment, “off state” light from the red, green, and blue DLP modulation may be reflected away from on-state light paths within the prism, tending to avoid uncontrolled scatter. In other embodiments, by keeping the colors separate for much of the prism path length, power levels may be significantly reduced at typical failure points. Light efficiency may be increased significantly when using discrete light sources like LEDs and lasers by removal of the additional red, green, and blue separation and re-combination losses.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Patent Application No. 62/240,287, filed on Oct. 12, 2015, U.S. Patent Application No. 62/200,417, filed on Aug. 3, 2015 and U.S. Provisional Patent Application No. 62/099,054, filed on Dec. 31, 2014, each of which is hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to projector systems and, particularly, to improved prisms systems for laser-based image projection systems. 
       BACKGROUND 
       [0003]    Projector systems are now being architected with improvements in dynamic range. Many of these types of improvements are in the area of laser projection systems. Some such laser projection systems may also comprise dual and multi-modulator projector display systems. It may be desirable to improve the performance of these improved image projection systems. 
         [0004]    Conventional high performance Digital Light Processing (DLP) projectors use a three-channel prism assembly having a common light path bi-directionally through the color prism where white light is split into red, green, and blue and then re-combined into a full-color (white light) image. After splitting the input white light into three colors, the colors are individually modulated by dedicated DLP chips and sent back through the same color prism to re-combine the modulated light into a full color image. 
         [0005]    Examples of such conventional prisms may be found in:
       (1) U.S. Pat. No. 3,659,918, to Tan, entitled “COLOR SEPARATING PRISM SYSTEM” and issued on May 2, 1972;   (2) U.S. Pat. No. 7,665,850, to Penn, entitled “PRISM FOR HIGH CONTRAST PROJECTION” and issued on Feb. 23, 2010; and   (3) U.S. Pat. No. 7,993,014, to Penn, entitled “PRISM FOR HIGH CONTRAST PROJECTION” and issued on Aug. 9, 2011   all of which are hereby incorporated by reference in their entirety.       
 
       SUMMARY 
       [0010]    In many embodiments of prism assemblies for projector display systems herein, the prism inputs are discrete color channels (e.g., red, green and blue channels)—as opposed to the white light input of the conventional prism assembly as described, but the modulated light may be still combined in a similar manner This may be desirable for a number of reasons. First, “off state” light from the red, green, and blue DLP modulation is reflected away from on-state light paths within the prism, tending to avoid uncontrolled scatter. Second, the re-combination of light may be done with a Philips-style prism (as in the related patent below), but with significantly simplified coatings, allowed by the narrow-band, uni-directional discrete red/green/blue illumination sources used with this prism. Third, by keeping the colors separate for much of the prism path length, power levels may be significantly reduced at typical failure points. This allows more optical power handling capability in the prism. And finally, light efficiency may be increased significantly when using discrete light sources like LEDs and lasers by removal of the additional red, green, and blue separation and re-combination losses usually found in typical three-channel prism designs. In general, many embodiments herein optimize individual light paths to minimize scattering, losses, and thermal loads in order to provide improved efficiency, contrast, and power handling in a 3-chip DLP projector. 
         [0011]    Coating optimization may be done to AR coatings and dichroic coatings that combine the light. The AR coatings on the input legs can be optimized per color (e.g., since each leg may see a single color) and angle (assuming higher f/#PSF relay is used). This optimization can result in better transmission (˜0.2% per surface, with 7 surfaces in each discrete path). The dichroic coatings can be optimized for narrowband light (assuming non-lamp source) which can have improved reflectance and transmission compared to broader band coatings, and also optimized for narrower angles (will vary depending on narrow band wavelength choices). Improvements in the dichroic coatings can also be critical to contrast ratio since light control is critical there and unintended reflections could reduce contrast. In other embodiments, this design may also be applied to single-chip DLP projector with monochromatic or color sequential operation. 
         [0012]    In many embodiments, prisms are capable of receiving discrete illumination inputs (e.g. which may tend to aid efficiency) from discrete color laser sources. In addition, many embodiments may tend to perform well with high power and tend to reduce heat load and thermal stresses to improve power handling and reliability 
         [0013]    In one embodiment, a prism assembly for an image projector display systems is disclosed, comprising: a plurality of discrete color light input; for each discrete color light input, a prism element to receive the discrete color light input; and wherein further the heating load for each said prism element is less than the if the prism element received full spectrum illumination. 
         [0014]    Other features and advantages of the present system are presented below in the Detailed Description when read in connection with the drawings presented within this application. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive. 
           [0016]      FIG. 1  depicts one schematic embodiment of an image projector display system as may be suitable for use of the improved prism input embodiments of the present application. 
           [0017]      FIG. 2  depicts one embodiment of a projector system that suffices for the purposes of the present application. 
           [0018]      FIG. 3  depicts another embodiment of a projector system that may suffice for the purposes of the present application. 
           [0019]      FIGS. 4A through 4C  depicts a conventional prism input system, as is known in the art. 
           [0020]      FIGS. 5A through 5D  show various light paths during the operation of conventional prism input system of  FIGS. 4A through 4C . 
           [0021]      FIGS. 6A through 6D  show one embodiment of a high contrast discrete input prism as made in accordance with the principles of the present application. 
           [0022]      FIGS. 7A through 7D  show various light paths during the operation of conventional prism input system of  FIGS. 6A through 6D . 
           [0023]      FIG. 8  depicts one exemplary plot of the thermal loading of the conventional prism as shown in  FIGS. 4A through 4C  while processing full light power of a projector system. 
           [0024]      FIG. 9  depicts one exemplary plot of the thermal loading of the high contrast discrete input prism as shown in  FIGS. 6A through 6D  while processing full light power of a projector system. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    As utilized herein, terms “component,” “system,” “interface,” and the like are intended to refer to a computer-related entity, either hardware, software (e.g., in execution), and/or firmware. For example, a component can be a process running on a processor, a processor, an object, an executable, a program, and/or a computer. By way of illustration, both an application running on a server and the server can be a component. One or more components can reside within a process and a component can be localized on one computer and/or distributed between two or more computers. A component may also be intended to refer to a communications-related entity, either hardware, software (e.g., in execution), and/or firmware and may further comprise sufficient wired or wireless hardware to affect communications. 
         [0026]    Throughout the following description, specific details are set forth in order to provide a more thorough understanding to persons skilled in the art. However, well known elements may not have been shown or described in detail to avoid unnecessarily obscuring the disclosure. Accordingly, the description and drawings are to be regarded in an illustrative, rather than a restrictive, sense. 
         [0027]    Introduction 
         [0028]    In the field of projector and other display systems, it is desirable to improve both image rendering performance and system efficiency. Several embodiments of the present application describe systems, method and techniques to affect these improvements by employing light field modeling for dual, or multi-modulation display systems. In one embodiment, light source models are developed and used to advantageous effect. Camera pictures of displayed images of known input images may be evaluated to improve light models. In some embodiments, an iterative process may accumulate improvements. In some embodiments, these techniques may be used on moving images to make live adjustments to improve image rendering performance 
         [0029]    Dual modulation projector and display systems have been described in commonly-owned patents and patent applications, including:
       (1) U.S. Pat. No. 8,125,702 to Ward et al., issued on Feb. 28, 2012 and entitled “SERIAL MODULATION DISPLAY HAVING BINARY LIGHT MODULATION STAGE”;   (2) United States Patent Application 20130148037 to Whitehead et al., published on Jun. 13, 2013 and entitled “PROJECTION DISPLAYS”;   (3) United States Patent Application 20110227900 to Wallener, published on Sep. 22, 2011 and entitled “CUSTOM PSFs USING CLUSTERED LIGHT SOURCES”;   (4) United States Patent Application 20130106923 to Shields et al., published on May 2, 2013 and entitled “SYSTEMS AND METHODS FOR ACCURATELY REPRESENTING HIGH CONTRAST IMAGERY ON HIGH DYNAMIC RANGE DISPLAY SYSTEMS”;   (5) United States Patent Application 20110279749 to Erinjippurath et al., published on Nov. 17, 2011 and entitled “HIGH DYNAMIC RANGE DISPLAYS USING FILTERLESS LCD(S) FOR INCREASING CONTRAST AND RESOLUTION” and   (6) United States Patent Application 20120133689 to Kwong, published on May 31, 2012 and entitled “REFLECTORS WITH SPATIALLY VARYING REFLECTANCE/ABSORPTION GRADIENTS FOR COLOR AND LUMINANCE COMPENSATION”.
           all of which are hereby incorporated by reference in their entirety.   
               
 
         [0037]    One Exemplary Physical Architecture 
         [0038]      FIG. 1  shows one possible embodiment of a suitable image projector display system. In this embodiment, the projector display system is constructed as a dual/multi-modulator projector display system  100  that may suffice for the purposes of the present application. Projector system  100  employs a light source  102  that supplies the projector system with a desired illumination such that a final projected image will be sufficiently bright for the intended viewers of the projected image. Light source  102  may comprise any suitable light source possible—including, but not limited to: Xenon lamp, laser(s), coherent light source, partially coherent light sources. As the light source is a major draw of power and/or energy for the entire projector system, it may be desirable to advantageously use and/or re-use the light, so as to conserve the power and/or energy during the course of its operation. 
         [0039]    Light  104  may illuminate a first modulator  106  that may, in turn, illuminate a second modulator  110 , via a set of optional optical components  108 . Light from second modulator  110  may be projected by a projection lens  112  (or other suitable optical components) to form a final projected image upon a screen  114 . First and second modulators may be controlled by a controller  116 —which may receive input image and/or video data. Controller  116  may perform certain image processing algorithms, gamut mapping algorithms or other such suitable processing upon the input image/video data and output control/data signals to first and second modulators in order to achieve a desired final projected image  114 . In addition, in some projector systems, it may be possible, depending on the light source, to modulate light source  102  (control line not shown) in order to achieve additional control of the image quality of the final projected image. 
         [0040]    Light recycling module  103  is depicted in  FIG. 1  as a dotted box that may be placed in the light path from the light source  102  to the first modulator  106 , as will be discussed below. While the present discussion will be given in the context of this positioning, it will be appreciated that light recycling may be inserted into the projector system at various points in the projector system. For example, light recycling may be placed between the first and second modulators. In addition, light recycling may be placed at more than one point in the optical path of the display system. While such embodiments may be more expensive due to an increase in the number of components, that increase may be balanced off against the energy cost savings as a result of multiple points of light recycling. 
         [0041]    While the embodiment of  FIG. 1  is presented in the context of a dual, multi-modulation projection system, it should be appreciated that the techniques and methods of the present application will find application in single modulation, or other dual, multi-modulation display systems. For example, a dual modulation display system comprising a backlight, a first modulator (e.g., LCD or the like), and a second modulator (e.g., LCD or the like) may employ suitable blurring optical components and image processing methods and techniques to affect the performance and efficiencies discussed herein in the context of the projection systems. 
         [0042]    It should also be appreciated that—even though  FIG. 1  depicts a two-stage or dual modulator display system—the methods and techniques of the present application may also find application in a display system with only one modulator or a display system with three or more modulator (multi-modulator) display systems. The scope of the present application encompasses these various alternative embodiments. 
         [0043]    One Light Recycling Embodiment 
         [0044]      FIG. 2  depicts one embodiment of a projector system, as may be suitable for the purposes of the present application. A light conduit subsystem/module (e.g., comprising one or more components from  201  to  216 ) may be placed in the projector system primarily between the light source  102  and a first modulator  221 . Light from light source  102  may be input to the optical path via an integrating rod/tube/box  202 . In one embodiment, integrating rod/tube/box  202  may comprise a substantially reflected surface in its interior, so that light that is incident on its surface may be reflected (e.g., possibly multiple times) until the light exits its extreme right end  203 . Once the light exits the integrating rod/tube/box, the light may be placed into an optical path that is defined by a set of optical elements—e.g., lens  204 ,  214  and  216  and a set of filters and/or polarizers  206 ,  208 ,  210  and  212 . This embodiment may also be constructed to perform light recycling, if desired for the design of this projector system. 
         [0045]    First modulator  221  may comprise a number of prisms  218   a,    218   b  and a reflector  220 . Reflector  220  may comprise a Digital Micromirror Device (DMD) array of reflectors, or a Micro-Electro-Mechanical System (MEMS) array—or any other suitable set of reflectors possible that may reflect light in at least two or more paths. One such path is depicted in  FIG. 2 . As may be seen, reflectors  220  direct the light onto the interface of prisms  218   a  and  218   b,  such that the light may be thereby reflected into lens assembly  222  and thereafter to second modulator  229  (e.g., comprising lens assembly  224 , prisms  226  and  230  and reflector  228 ). This light may be employed to form the finally projected image to be viewed by an audience. 
         [0046]    However, at certain time during the rendering of the final projected image, the full power/energy of the light source  102  may not be needed. If it is not possible to modulate the power of light source  102 , then it may be desired to recycle the light from light source  102 . Additionally, it may be desired to increase the brightness of “highlights” in an image—and light recycled in the projector system may provide additional power. In such a case, and as may be seen in  FIG. 2 , it may be possible to align reflector  220  from its current position as shown (i.e., where the light is directed to travel the path down to the second modulator—to position instead where the light would be substantially reflected back to the integrating rod/tube/box  202 , along substantially the same path as described as traveling from right-to-left direction. 
         [0047]    In another embodiment, a third optional path (not shown) allows the reflectors to direct light from the light source to a light “dump”—i.e., a portion of the projector system where the light is absorbed. In this case, the light is wasted as heat to be dissipated from the projector system. Thus, the projector system may have multiple degrees of freedom when it comes to directing the light as desired. 
         [0048]      FIG. 3  is yet another embodiment of a portion of a projector system  300 —which may serve to transmit light from at least one laser and/or partially coherent colored light source and ports (e.g., through fiber launch  302 , collimator  304 , diffuser  306 ). Light from such a source may transmit through a first optical subsystem/diffuser relay  308  to condition the light to be input into integrating rod  312 —which may comprise the reflecting proximal end  310  (e.g., recycling mirror). A second optical subsystem/recycling relay  314  may further condition the light as desired prior to input into a first modulator  316 . As with  FIG. 2  above, this first leg of the system  300  may affect a light recycling mode, as discussed. 
         [0049]    After first modulation, light may be transmitted through a third optical subsystem/Point Spread Function (PSF) relay  318  prior to input into a second modulator  320 —which modulates the light for transmission through a projector optical subsystem  322  to project a final image for viewing. In continued reference to  FIG. 3 , there is shown a relay optical system  318  that is placed in between a first modulator  316  (e.g., a pre-modulator) and a second modulator  320  (e.g., a primary modulator/nine piece prism). Such a relay optical system may be desirable to both reduce the amount of artifacts in the image processing—as well as increasing the contrast of the projected image. 
         [0050]    As discussed herein in the context of one embodiment, it may be desirable for the first modulator/pre-modulator to produce a blurred and/or de-focused image based upon image data values, e.g., such as a halftone image. In many embodiments, it may be desirable to have a relay optical system that tends to produce a uniformly blurred/de-focused image from the pre-modulator to the primary modulator. In addition, it may be desirable to have a desired, defocused spot shape for this embodiment. 
         [0051]    In many embodiments, the relay optical system may comprise lenses or other optical elements that effectively moves the focal plane, corrects for any coma, and adjusts the spread (e.g., by creating defocus/blur and adding spherical aberration to some desired amount). 
         [0052]    Improved Prism Embodiment 
         [0053]    As discussed above, it may be desirable to improve the efficiency of these projector systems, both in terms of energy efficiency and/or in terms of cost efficiency. One such area for improvement may be made in the area of the input prism assembly, e.g., as employed in conjunction with a Spatial Light Modulator (SLM)—such as a DMD and/or MEMS array as described herein. 
         [0054]      FIGS. 4A through 4C  depict a conventional prism assembly in front view, top view and side view, respectively. In operation,  FIGS. 5A through 5D  depict how the prism assembly may interact with an input light beam, reflect the light beam off the DMD in ON state, OFF state and FLAT state orientations of the DMD reflectors, respectively. 
         [0055]    As may be seen in  FIGS. 4A through 4C  and  FIGS. 5A through 5D , an input light beam  502  may be transmitted through first prism  408  and Totally Internally Reflected (TIR) at the interface with second prism  406 , transmitted through optical glasses  404  and  400 —which is disposed proximal to DMD array  500  (depicted as light beam  504 ). 
         [0056]    As depicted in  FIG. 5B , when the DMD reflector is set to ON state, reflected light beam  506  may be transmitted back through optical elements  400 ,  404 ,  408  and  406 —to provide light for further modulation and/or projection.  FIG. 5C  depicts the light beam  508 , as may be reflected when the DMD reflector is set to the OFF state—e.g., whereby light beam  508  may be directed to a light dump (not shown), to be absorbed and/or disposed of, so as not to affect the dynamic range of the display.  FIG. 5D  depicts light beam  510  when the DMD reflectors are in a FLAT state orientation. As with light reflected from the DMD in the OFF state, light reflected during the FLAT state should similarly be directed away from an operative downstream light path which might include further modulation and/or projection. 
         [0057]    When the light source is high powered, such as high powered white light (e.g. Xenon lamp or the like) or high powered colored laser light, then heat may present undesired thermal effects that may manifest themselves in either undesirable imaging effects and/or mechanical element degradation. Undesirable effects may include change in PSF shape and/or size and positional drift of image from pre-mod to primary modulator over time and heat cycling. 
         [0058]      FIGS. 6A through 6D  show one embodiment of a prism assembly as made in accordance with the principles of the present application—given a front view, top view, side view and bottom view, respectively. As may be seen, the present prism assembly comprises optical elements  600 ,  602 ,  604 ,  606 ,  608 ,  610 ,  612 ,  614  and  616 . In this embodiment, optical elements may be employed to operate on one or more color channels—making separate color channel prism paths for each separate color light that is received by the prism assembly. 
         [0059]    For example, in the green channel as one of the separate color channel prism paths, optical element  602  is a green dump wedge, optical element  612  is a green wedge and optical element  600  is a green input wedge. In the blue channel, optical element  608  is a blue input wedge, optical element  610  is a blue dump wedge and optical element  616  is a blue wedge. In the red channel, optical element  606  is a red dump wedge, optical element  614  is a red wedge and optical element  604  is a red input wedge. It should be noted that each color channel has a number of optical elements deployed for the processing of the colored light input. 
         [0060]    It should be appreciated that while one embodiment may take in separate colored light input (e.g., from lasers, LEDS, partially coherent light sources or the like), other embodiments may take in white light input (e.g., from Xenon lamp or the like). In such embodiments, it may be possible to separate the various color components from the white light prior to prism assembly (e.g., with another, initial, prism assembly or the like) and then process the separate color components with the prism assembly as made in accordance with the principles of the present application. 
         [0061]    In operation,  FIGS. 7A through 7D  depict the manner in which input light beams would be processed by the prism assembly of the present application.  FIG. 7A  depicts the situation where a beam of green light (e.g., from white light, green laser light and/or partially coherent green light) is input into the system (as beam  702 ). Beam  702  reflects off the surface of wedge  600  as shown and transmitted to the DMD reflector  700  (as beam  704 ). 
         [0062]      FIG. 7B  depicts the reflected beam  708  when the DMD reflector is set in the ON state. Beam  708  is transmitted through the green wedge  612  for further modulation and/or projection.  FIG. 7C  depicts the reflected beam  708  when the DMD reflector is set in the OFF state. Beam  708  is transmitted through the green dump wedge  602 —to prevent further modulation and/or projection.  FIG. 7D  depicts the reflected beam  708  when the DMD reflector is set in the FLAT state. Beam  708  is again transmitted through the green dump wedge  602 —to again prevent further modulation and/or projection. 
         [0063]    Improved Thermal Profile 
         [0064]    As mentioned above, today&#39;s projector systems are illuminated with higher power light sources. Such light sources may include Xenon white lamps, high powered colored lasers, and/or high powered partially coherent light sources. The performance of such prior art prism designs may not be desirable for many reasons in high powered image projector display system. For merely one example,  FIG. 8  depicts the thermal load of the conventional prism (e.g., same or similar prism as shown as  FIGS. 4A through 4C ). 
         [0065]    As may be seen, the thermal loads in the legend proceed from lowest to highest as: 1× ( 802 ), 2× ( 804 ), 3× ( 806 ), 4× ( 808 ) and 6× ( 810 ). As may be seen the prior art prism—under full illumination—purports to have many regions of high thermal load as noted. 
         [0066]    By contrast,  FIG. 9  depicts the thermal loading of the 9-piece prism arrangement of  FIGS. 6A through 6D , and other embodiments as made in accordance with the principles of the present application. In this embodiment, as the prism assembly may input separate, discrete color channels of illumination, it may be seen that the thermal loading of this prism assembly is better distributed. 
       Alternative Embodiments 
       [0067]    As discussed herein, several alternative embodiments may include:
       (1) Significantly Simplified Dichroic Coatings   (2) Single pass at single nominal angle unlike current 3-chip prisms. (For example, it may not go through the color prism on entry at a different angle through the wedges/coatings.)   (3) f/4.5 has significantly smaller angular spread   (4) 2-3× thermal absorption margin on every element   (5) Natively higher contrast due to reduced scatter   (6) Reduction/Elimination of back scatter from illumination path (For example, due to one less pass through the dichroics and some of the AR coatings.)   (7) Reduction/Elimination of forward scatter from off state light path in color prism. (For example, due to one less pass through the dichroics and some of the AR coatings.)   (8) Shorter color prism to reduce cost   (9) Removes color combine/separation losses for laser source on current dual 6 piece prism design   (10) Discrete light dump for each color for higher power and/or improved thermal management       
 
         [0078]    In many embodiments, the following ranges of f/# may suffice: f/2 to f/3 for non-laser illumination and f/4 to f/8 for laser illumination. For some preferred embodiments, the range can be f/2.4 to f/3 for non-laser illumination and f/4 to f/5 for laser illumination. Specific examples may include f/2.4 for typical xenon and f/4.5 for typical laser. 
         [0079]    Coating optimization may be done to Anti-Reflective (AR) coatings and dichroic coatings that combine the light. The AR coatings on the input legs can be optimized per color (e.g., since each leg may see a single color) and angle (assuming higher f/#PSF relay is used). This optimization can result in better transmission (˜0.2% per surface, with 7 surfaces in each discrete path). In some cases, the angle is in reference to ‘angle of incidence’—where, in some cases for lower angles, it may be easier to get better coating transmissions. The dichroic coatings can be optimized for narrowband light (assuming non-lamp source) which can have improved reflectance and transmission compared to broader band coatings, and also optimized for narrower angles (will vary depending on narrow band wavelength choices). In some embodiments, coatings may be applied at various interfaces in the prism assembly. For example, in  FIG. 6D , a red reflect/green transmit dichroic coating may be applied at the interface between  612  and  614 . A blue reflect/green and red transmit dichroic coating may be applied at the interface between  614  and  616 . As input light does not go through the coatings in its entirety, it tends to avoid the opportunity to scatter or partially reflect. 
         [0080]    Improvements in the dichroic coatings can also be useful to contrast ratio since light control may be desirable there and any unintended reflections may reduce contrast. In other embodiments, this design may also be applied to single-chip DLP projector with monochromatic or color sequential operation. 
         [0081]    A detailed description of one or more embodiments of the invention, read along with accompanying figures, that illustrate the principles of the invention has now been given. It is to be appreciated that the invention is described in connection with such embodiments, but the invention is not limited to any embodiment. The scope of the invention is limited only by the claims and the invention encompasses numerous alternatives, modifications and equivalents. Numerous specific details have been set forth in this description in order to provide a thorough understanding of the invention. These details are provided for the purpose of example and the invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the invention is not unnecessarily obscured.