Abstract:
A projection system comprising an illumination relay, a coupling lens, a modulation device, and a projection lens is provided. The illumination relay is configured to provide an illumination beam to the coupling lens along an illumination path having a first optical axis. The coupling lens is configured to direct the illumination beam onto the modulation device. The modulation device is configured to modulate the illumination beam to form an imaging beam and reflect the imaging beam into the coupling lens. The coupling lens is configured to direct the imaging beam into the projection lens along a projection path having a first optical axis such that the second optical axis is substantially parallel with the first optical axis.

Description:
BACKGROUND  
       [0001]     Optical architectures of digital projectors typically include an illumination system, projection system, an optical modulator and one or more devices that couple the illumination system, projection system and the optical modulator. The illumination system illuminates the optical modulator. The optical modulator produces images by modulating the light falling across it by either reflecting or transmitting the light. The projection system images the optical modulator on the screen by capturing the modulated illumination of the optical modulator.  
         [0002]     Generally, optical architectures have the optical axes of the projection and illumination paths either overlapping (across a portion of the system) or tilted substantially with respect to each other. For those systems that require or might benefit from a relatively on-axis or small incident angle illumination and projection paths on the optical modulator plane, such architectures may be inefficient, noisy, bulky or expensive. It would be desirable to be able to obtain high efficiency and low stray light in a compact package at a low cost in an optical architecture.  
       SUMMARY  
       [0003]     One form of the present invention provides a projection system comprising an illumination relay, a coupling lens, a modulation device, and a projection lens. The illumination relay is configured to provide an illumination beam to the coupling lens along an illumination path. The coupling lens is configured to direct the illumination beam onto the modulation device. The modulation device is configured to modulate the illumination beam to form an imaging beam and reflect the imaging beam into the coupling lens. The coupling lens is configured to direct the imaging beam into the projection lens along a projection path that is substantially parallel with the illumination path. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]      FIG. 1  is a block diagram illustrating an offset digital projection system according to one embodiment of the present invention.  
         [0005]      FIG. 2  is a schematic diagram illustrating an offset digital projection system according to one embodiment of the present invention.  
         [0006]      FIG. 3  is a schematic diagram illustrating an offset digital projection system according to one embodiment of the present invention.  
         [0007]      FIG. 4  is a flow chart illustrating a method for projecting an image using an offset digital projection system according to one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0008]     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense.  
         [0009]     As described herein, an optical architecture is provided for a digital projector that sets the optical axes of an illumination system and a projection system to be parallel and offset with respect to each other using a coupling lens. The coupling lens allows the sharing of projection and illumination path spaces while maintaining the separation of the actual projection and illumination beams. By doing so, the architecture effectively separates the illumination and projection beam paths throughout the system.  
         [0010]      FIG. 1  is a block diagram illustrating one embodiment of an offset digital projection system  10 . In projection system  10 , an illumination source  102  generates and emits an illumination beam to an illumination relay  106  along an optical path  104 . Illumination relay  106  integrates and collimates the illumination beam and provides the illumination beam to a coupling lens  110  along an illumination path  108  such that an optical axis of illumination path  108  is parallel or substantially parallel to a normal  100  to a plane  101  of a modulation device  114 . Normal  100  is substantially perpendicular to plane  101 , and plane  101  aligns with the modulating elements (not shown) of modulation device  114 . Coupling lens  110  directs and focuses the illumination beam onto modulation device  114  along an illumination path  112 . Illumination relay  106  images illumination source  102  onto modulation device  114  via coupling lens  110  such that modulation device  114  is uniformly illuminated with minimum overfill. Coupling lens  110  directs the illumination beam onto modulation device  114  at a non-zero angle of incidence. Coupling lens  110  is substantially centered with respect to modulation device  114 .  
         [0011]     Modulation device  114  modulates the illumination beam from coupling lens  110  according to an input signal, e.g., a computer or video input signal, (not shown) to form an imaging beam. The imaging beam is reflected from modulation device  114  through coupling lens  110  along an optical path  116 . Coupling lens  110  directs the imaging beam from modulation device  114  through a projection lens  120  along a projection path  118  that an optical axis of projection path  118  is parallel or substantially parallel to normal  100  and the optical axis of illumination path  108 . Projection lens  120  focuses and may zoom the imaging beam along an optical path  122  to cause still or video images to be formed on a screen or other display surface. Projection lens  120  images modulation device  114  through coupling lens  110  onto the screen or other display surface used for final display.  
         [0012]     In projection system  10 , illumination relay  106 , coupling lens  110 , and projection lens  120  are situated so as to minimize the overlap of the illumination and imaging beams along illumination path  108  and projection path  118 . In particular, the illumination beam and the imaging beam each intersect different areas of an optical pupil plane  124  of the system such that the imaging beam is spatially separated from the illumination beam at pupil plane  124 . Accordingly, illumination path  108  is effectively separated from projection path  118 . As shown in  FIG. 1 , coupling lens  110  includes all optical elements between pupil plane  124  and modulation device  114 .  
         [0013]     Illumination source  102  may be a mercury ultra high pressure, xenon, metal halide, or other suitable projector lamp that provides a monochromatic or polychromatic illumination beam. Modulation device  114  transmits or reflects selected portions of the illumination beam through coupling lens  110  and projection lens  120  in response to an image input signal (not shown) to cause images to be projected onto a screen or other surface. Modulation device  114  comprises at least one digital modulator such as a spatial light modulator like LCos, liquid crystal display (LCD), digital micromirror display (DMD) or other type. In one embodiment, modulation device  114  includes a separate digital modulator for each color, e.g., red, blue, and green.  
         [0014]      FIG. 2  is a schematic diagram illustrating one embodiment of an offset digital projection system  10 A. In projection system  10 A, illumination source  102  generates and emits an illumination beam  202  to an illumination relay  106 A along an optical path  104 . Illumination relay  106 A includes an integrating rod  200  that integrates illumination beam  202  and an illumination lens  204  that collimates illumination beam  202  and provides illumination beam  202  to a fold mirror  206 . Illumination lens  204  includes lenses  204 A,  204 B, and  204 C.  
         [0015]     Fold mirror  206  reflects illumination beam  202  from illumination lens  204  through a coupling lens  110 A along an illumination path such that an optical axis of the illumination path of illumination beam  202  is parallel or substantially parallel to an optical axis of modulation device  114  between fold mirror  206  and coupling lens  110 A. In the embodiment shown in  FIG. 2 , fold mirror  206  reflects illumination beam  202  at an angle of approximately ninety degrees between the optical axis of illumination lens  204  and the optical axis of coupling lens  110 A. In other embodiments, fold mirror  206  may be positioned differently to reflect illumination beam  202  at any non-zero angle between the optical axis of illumination lens  204  and the optical axis of coupling lens  110 A.  
         [0016]     Coupling lens  110 A refracts and focuses illumination beam  202  onto modulation device  114  through a beamsplitter  210 . Beamsplifter  210  separates illumination beam  202  into separate components (e.g., red, blue, and green components) that are provided to different modulators  114 A,  114 B, and  114 C of modulation device  114 . Modulators  114 A,  114 B, and  114 C may be set in any suitable arrangement with respect to beamsplitter  304 . Beamsplitter  210  may be a dichroic prism, a dichroic plate, a dichroic x-cube, or other element configured to separate illumination beam  202  into separate components. Beamsplitter  210  may be omitted in embodiments where modulation device  114  includes a single modulator. Coupling lens  110 A refracts illumination beam  202  onto modulation device  114  at a non-zero angle of incidence. Coupling lens  110 A, as shown, includes three lenses:  208 A,  208 B and  208 C to refract illumination beam  202 . In other embodiments, coupling lens  110 A may be a combination of one or more spherical or aspherical lenses.  
         [0017]     Modulation device  114  modulates the illumination beam from coupling lens  110 A according to an input signal, e.g., a computer or video input signal, (not shown) to form an imaging beam  212 . Imaging beam  212  is reflected from modulation device  114  through beamsplitter  210  and into coupling lens  110 A. Coupling lens  110 A refracts imaging beam  212  from modulation device  114  through a projection lens  120 A using lenses  208 A,  208 B, and  208 C such that imaging beam  212  travels along an optical axis of a projection path that is parallel or substantially parallel to normal  100  to plane  101  of modulation device  114  and an optical axis of the illumination path of illumination beam  202  between coupling lens  110 A and an optical pupil plane  214 .  
         [0018]     Projection lens  120 A focuses and may zoom imaging beam  212  along an optical path to cause still or video images to be formed on a screen or other display surface. Projection lens  120 A, as shown, includes four lenses:  216 A,  216 B,  216 C, and  216 D. In other embodiments, projection lens  120 A may be a combination of one or more spherical or aspherical lenses or mirrors.  
         [0019]     In projection system  10 A, illumination relay  106 A, coupling lens  110 A, and projection lens  120 A are situated so as to minimize the overlap of illumination beam  202  and imaging beam  212  along the respective illumination and projection paths. In particular, the illumination beam and the imaging beam each intersect different areas of pupil plane  214  of the system such that imaging beam  212  is spatially separated from illumination beam  202  at pupil plane  214 . Accordingly, the illumination path is effectively separated from the projection path. As shown in  FIG. 2 , coupling lens  110 A comprises all optical elements between pupil plane  214  and modulation device  114 .  
         [0020]      FIG. 3  is a schematic diagram illustrating one embodiment of an offset digital projection system  10 B. In projection system  10 B, illumination source  102  generates and emits an illumination beam to illumination relay  106  along an optical path  104 . Illumination relay  106  integrates and collimates the illumination beam and provides the illumination beam to coupling lens  110 B along an illumination path  108  such that an optical axis of illumination path  108  is parallel or substantially parallel to normal  100  to plane  101  of modulation device  114  between illumination relay  106  and coupling lens  110 B.  
         [0021]     Coupling lens  110 B refracts and focuses the illumination beam onto modulation device  114  through a beam splitter  304 . Beam splitter  304  separates the illumination beam into separate components (e.g., red, blue, and green components) that are provided to different modulators  114 A,  114 B, and  114 C of modulation device  114 . Modulators  114 A,  114 B, and  114 C may be set in any suitable arrangement with respect to beamsplitter  304 . Beamsplitter  304  may be a dichroic prism, a dichroic plate, a dichroic x-cube, or other element configured to separate the illumination beam into separate components. Beamsplitter  304  may be omitted in embodiments where modulation device  114  includes a single modulator. Coupling lens  110 B refracts the illumination beam onto modulation device  114  at a non-zero angle of incidence as indicated by an optical path  112 . Coupling lens  110 B, as shown, includes three lenses:  302 A,  302 B and  302 C to refract the illumination beam. In other embodiments, coupling lens may be a combination of one or more spherical or aspherical lenses.  
         [0022]     Modulation device  114  modulates the illumination beam from coupling lens  110 A according to an input signal, e.g., a computer or video input signal, (not shown) to form an imaging beam. The imaging beam is reflected from modulation device  114  along an optical path  116  through beamsplitter  304  and into coupling lens  110 B. Coupling lens  110 B refracts the imaging beam from modulation device  114  to a fold mirror  306  using lenses  302 A,  302 B, and  302 C such that the imaging beam travels along an optical axis of a projection path  118  that is parallel or substantially parallel to normal  100  to plane  101  of modulation device  114  and an optical axis of illumination path  108  of the illumination beam.  
         [0023]     Fold mirror  306  reflects the imaging beam from coupling lens  110 B into projection lens  120  along an optical path  308 . In the embodiment shown in  FIG. 3 , fold mirror  306  reflects the imaging beam at an angle of approximately ninety degrees between normal  100  and optical axis  308  of projection lens  120 . In other embodiments, fold mirror  306  may be positioned differently to reflect the imaging beam at any non-zero angle between normal  100  and optical axis  308  of projection lens  120 . Projection lens  120  focuses and may zoom the imaging beam from fold mirror  306  along optical path  122  to cause still or video images to be formed on a screen or other display surface.  
         [0024]     In projection system  10 B, illumination relay  106 , coupling lens  110 B, and projection lens  120  are situated so as to minimize the overlap of the illumination and imaging beams along illumination path  108  and projection path  118 . In particular, the illumination beam and the imaging beam each intersect different areas of pupil plane  124  of the system such that the imaging beam is spatially separated from the illumination beam at pupil plane  124 . Accordingly, illumination path  108  is effectively separated from projection path  118 .  
         [0025]      FIG. 4  is a flow chart illustrating one embodiment of a method for projecting an image using an offset projection system. In  FIG. 4 , an illumination beam is provided from an illumination relay to a coupling lens as indicated in a block  402 . The illumination beam is directed onto a modulation device using the coupling lens as indicated in a block  404 . The illumination beam is modulated to form an imaging beam using the modulation device as indicated in a block  406 . The imaging beam is directed parallel or substantially parallel to the illumination beam and a normal to the plane of the modulation device to a projection lens using the coupling lens as indicated in a block  408 . The imaging beam is focused and may be zoomed in or out using the projection lens as indicated in a block  410 .  
         [0026]     In other embodiments, one or both of fold mirrors  206  and  306  may replaced with other reflective surfaces. In addition, a system may include fold mirrors in both the illumination and projection paths in other embodiments.  
         [0027]     An offset optical architecture as described herein may effectively separate the illumination and projection paths while maintaining the optical performance and highest possible efficiency and minimizing stray light. This architecture may also avoid complex and expensive optical components and may allow for a compact package that has a maximum number of small sized lenses to achieve a low cost compact system.  
         [0028]     Although specific embodiments have been illustrated and described herein for purposes of description of the preferred embodiment, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. Those with skill in the optical, mechanical, electro-mechanical, electrical, and computer arts will readily appreciate that the present invention may be implemented in a very wide variety of embodiments. This application is intended to cover any adaptations or variations of the preferred embodiments discussed herein. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.  
         [0029]     What is claimed is: