Abstract:
An optical engine includes adjustable optics that provide rapid and accurate alignment to imagers. The adjustable optics include a light pipe translatable along a first direction, (2) a focusing lens translatable along second and third directions, (3) a turning mirror translatable along the first, the second, and the third directions, and rotatable about the first and the second directions, and (4) an adjustable dichroic mirror rotatable about the third direction. The light pipe homogenizes light from a light source, the focusing lens focuses the homogenized light, a fixed dichroic mirror passes a first color light and reflects second and third color lights from the focused light, the turning mirror turns the second and the third color lights, and the adjustable dichroic mirror passes the second color light and reflects the third color light. The imagers reflect the color lights to form color images that combine to form a projected image.

Description:
FIELD OF INVENTION  
       [0001]     This invention relates to optical engines for displays, including rear projection televisions.  
       DESCRIPTION OF RELATED ART  
       [0002]     U.S. Pat. No. 6,857,752 discloses various optical engines. Particularly,  FIGS. 7 and 8  illustrate systems that utilize three imagers to project video images. With the high number of optical components in each system, the alignment of the optical components becomes slow and difficult. Thus, what are needed are an apparatus and a method that provide rapid and accurate alignment of the optical components in an optical engine.  
       SUMMARY  
       [0003]     In one embodiment of the invention, an optical engine includes adjustable optical components that provide rapid and accurate alignment of color lights to imagers. A light pipe homogenizes light from a light source, a focusing lens focuses the homogenized light, a first dichroic mirror passes a first color light and reflects second and third color lights from the focused light, a turning mirror turns the second and the third color lights, and a second dichroic mirror passes the second color light and reflects the third color light. The imagers reflect the color lights to form color images that combine to form a projected image.  
         [0004]     In one embodiment, the light pipe is translatable along a first direction to match the focal point of the light source. The focusing lens is translatable along second and third directions to match the first color light to a first imager. The turning mirror is (1) translatable along the first, the second, and the third directions, and (2) rotatable about the first and the second directions, to match the second color light to a second imager. The second dichroic mirror is rotatable about the third direction to match the third color light to a third imager. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]      FIG. 1A  illustrates a block diagram of an optical engine in one embodiment of the invention.  
         [0006]      FIG. 1B  illustrates a side view of the optical engine of  FIG. 1A  in one embodiment of the invention.  
         [0007]      FIGS. 2A and 2B  illustrate assembled and exploded view of an adjustable light pipe holder in one embodiment of the invention.  
         [0008]      FIGS. 3A and 3B  illustrate assembled and exploded view of an adjustable focus lens holder in one embodiment of the invention.  
         [0009]      FIGS. 4A and 4B  illustrate assembled and exploded view of an adjustable turning mirror holder in one embodiment of the invention.  
         [0010]      FIGS. 5A and 5B  illustrate assembled and exploded view of an adjustable dichroic mirror holder in one embodiment of the invention.  
         [0011]      FIG. 6  illustrates a flowchart of a method for calibrating the optical engine of  FIG. 1A  in one embodiment of the invention. 
     
    
       [0012]     Use of the same reference numbers in different figures indicates similar or identical elements.  
       DETAILED DESCRIPTION  
       [0013]      FIGS. 1A and 1B  illustrate an optical engine  100  in one embodiment of the invention. Optical engine  100  provides rapid and accurate alignment of color lights onto imagers.  
         [0014]     Optical engine  100  includes a UHP (ultra-high performance) lamp  102  that generates white light. Lamp  102  includes an elliptical reflector that focuses the white light to the input end of a light pipe  104 . Note that other light sources may be used in place of lamp  102 , and other light integrators may be used in place of light pipe  104 .  
         [0015]     Light pipe  104  homogenizes the intensity of the white light. Uniform white light exits generally along the positive X-direction from the output end of light pipe  104 . In one embodiment, light pipe  104  is made of glass and has a rectangular cross-section to generate either a rectangular white light having the aspect ratio of the display (e.g., 16:9 or 4:3). To accommodate variations in each lamp  102 , the location of light pipe  104  along the X-direction can be adjusted to align the input end of light pipe  104  to the focal point of lamp  102 .  
         [0016]     Referring to  FIGS. 2A and 2B , an adjustable light pipe holder  200  provides the mechanism for adjusting the location of light pipe  104  in one embodiment of the invention. Light pipe holder  200  includes a sleeve  202  and a bracket  204 . Sleeve  202  encases light pipe  104  and has a vertical tab  206  that extends from the body of sleeve  202 . Bracket  204  defines a guide  208  along the X-direction for receiving sleeve  202 . Guide  208  defines a slot  210  from which vertical tab  206  passes through. The location of light pipe  104  along the X-direction is adjusted by sliding vertical tab  206  to translate sleeve  202  in guide  208  of bracket  204 . The location of light pipe  104  is fixed by applying adhesive (e.g., UV glue) between the bottom of tab  206  and slot  210 .  
         [0017]     Referring back to  FIGS. 1A and 1B , a polarizer  106  receives the uniform white light from light pipe  104  and passes part of the white light having one polarization (e.g., s-polarized white light). Polarizer  106  may be a wire-grid polarizer made of glass embedded with fine aluminum ribbons.  
         [0018]     A focusing lens  108  receives the s-polarized white light from polarizer  106  and focuses the white light generally along the positive X-direction. Focusing lens  108  may be an aspheric lens. To accommodate variations in the components of engine  100 , the location of focusing lens  108  along the Y and the Z-directions can be adjusted to align a red color light to an imager  124 .  
         [0019]     Referring to  FIGS. 3A and 3B , an adjustable focusing lens holder  300  provides the mechanism for adjusting the location of focusing lens  108  along the Y and the Z-directions. Focusing lens holder  300  includes a top plate  302 , a mid plate  304 , and a base plate  306  held together with clips  308  on the sides of the plates. Top plate  302  includes retainers for holding focusing lens  108 . A screw  310  passes through a tab  312  of mid plate  304  and threads onto a tab  314  of top plate  302 . By turning screw  310 , the location of lens  108  along the Y-direction is adjusted. A screw  316  passes through a tab  318  of base plate  306  and threads onto a tab  320  of mid plate  304 . By turning screw  316 , the location of lens  108  along the Z-direction is adjusted.  
         [0020]     Referring back to  FIGS. 1A and 1B , a dichroic mirror  110  receives the white light from focusing lens  106 . In one embodiment, dichroic mirror  110  passes the red light and reflects blue and green lights. Oriented at  45  degrees to the X and the Y plane, dichroic mirror  110  passes the red light generally along the positive X-direction and reflects the blue and the green light generally along the positive Z-direction. Note that other color separators may be used in place of dichroic mirror  110 .  
         [0021]     Following the path of the red light, a pair of relay lenses  112  and  114  passes the red light generally along the positive X-direction to an input face  116  of a polarizing beam splitter (PBS)  118  (only visible in  FIG. 1A ). Relay lenses  112  and  114  eliminate any differences in the shape of the red light from the blue and the green lights due to their different optical paths. The red light will be uniform and collimated after passing through lenses  108 ,  112 , and  114 . In one embodiment, relay lenses  112  and  114  are spherical lenses. PBS  118  has a polarizing surface  120  (only visible in  FIG. 1A ) that reflects the s-polarized red light generally along the negative Z-direction through an imager face  122  (only visible in  FIG. 1A ).  
         [0022]     A liquid crystal on silicon (LCOS) imager  124  is located opposite of imager face  122  to receive the s-polarized red light. In one embodiment, LCOS imager  124  is mounted on imager face  122 . LCOS image  124  reflects the s-polarized red light and modulates part of the s-polarized red light to generate a red image having p-polarized red light. The red image travels in the positive Z-direction back towards PBS  118 . Polarizing surface  120  of PBS  118  passes the red image having the p-polarized red light to an input face  126  (only visible in  FIG. 1A ) of an X-cube color combiner  128  (only visible in  FIG. 1A ). In one embodiment, PBS  118  is mounted on input face  126 . Note that other types of imagers may be used in place of LCOS imager  124 .  
         [0023]     Referring back to the path of the blue and green lights, a turning mirror  130  reflects the blue and green lights generally along the positive X-direction. To accommodate variations in the components of engine  100 , the location of turning mirror  130  along the X, Y, and Z-directions, and the angle of turning mirror  130  about the X and the Y-directions, can be adjusted to align the blue color light to an imager  144 .  
         [0024]     Referring to  FIGS. 4A and 4B , mirror  130  is mounted on a plate  402 . Plate  402  has a pole  404  extending from an opposite surface. An adjustable mirror holder  405  provides the mechanism for adjusting the location of turning mirror  130  along the X, the Y, and the Z-directions, and the angle of turning mirror  130  about the X and the Y-directions. Pole  404  from plate  402  is received by a grip  406  mounted on a goniometer  408  that provides rotation about the X-direction. Goniometer  408  has a base and a table that rotates about the base when a knob is turned. Goniometer  408  is mounted on a stage  410  that provides translation along the Z-direction when a knob is turned. Stage  410  is mounted on a stage  412  that provides translation along the X-direction when a knob is turned. Stage  412  is mounted on a stage  414  that provides translation along the Y-direction when a knob is turned. Stage  414  is mounted on a goniometer  416  that provides rotation about the Y-direction when a knob is turned. Thus, adjustable mirror holder  403  provides 5-degrees of freedom to turning mirror  130 . In one embodiment, adjustable mirror holder  405  is part of optical engine  100 . In another embodiment, adjustable mirror holder  405  is only used to adjust turning mirror  130  during the manufacturing of optical engine  100  and is removed after turning mirror  130  is fixed to optical engine  100 .  
         [0025]     Referring back to  FIGS. 1A and 1B , a relay lens  132  passes the blue and the green lights generally along the positive X-direction. In one embodiment, relay lens  132  is an aspheric lens. The green light will be uniform and collimated after passing through lenses  108  and  132 .  
         [0026]     A dichroic mirror  134  receives the blue and the green lights from relay lens  132 . In one embodiment, dichroic mirror  134  passes the blue light and reflects the green light. Oriented about  45  degrees to the X and Y plane, dichroic mirror  134  passes the blue light generally along the positive X-direction and reflects the green light generally along the negative Z-direction. To accommodate variations in the components of engine  100 , the angle of dichroic mirror  134  about the Y-direction can be adjusted to align the green color light to an imager  156 . Note that other color separators may be used in place of dichroic mirror  134 .  
         [0027]     Referring to  FIGS. 5A and 5B , an adjustable dichroic mirror holder  500  provides the mechanism for adjusting the angle of dichroic mirror  134  about the Y-direction. A support frame  502  comprises slotted sides for receiving dichroic mirror  134 . Support frame  502  further includes pins  506  along the sides, which are received by bores  508  in brackets  510  so that mirror frame  502  can rotate about the Y-direction. In one embodiment, brackets  510  are mounted on color combiner  128 . The angle of dichroic mirror  134  is fixed by applying adhesives to pins  506  and bores  508 .  
         [0028]     Referring back to  FIG. 1A  and following the path of the blue light, a PBS  136  receives the blue light at an input face  138 . PBS  136  has a polarizing surface  140  that reflects the s-polarized red light generally along the positive Z-direction through an imager face  142 .  
         [0029]     A LCOS imager  144  is located opposite of imager face  142  to receive the s-polarized blue light. In one embodiment, LCOS imager  144  is mounted on imager face  142 . LCOS image  144  reflects the s-polarized blue light and modulates part of the s-polarized blue light to generate a blue image having p-polarized red light. The blue image travels in the negative Z-direction back towards PBS  136 . Polarizing surface  140  of PBS  136  passes the blue image having the p-polarized blue light to an input face  146  of color combiner  128 . In one embodiment, PBS  136  is mounted on input face  146 . Note that other types of imagers may be used in place of LCOS imager  144 .  
         [0030]     Following the path of the green light, a PBS  148  receives the green light at an input face  150 . PBS  148  has a polarizing surface  152  that reflects the s-polarized green light generally along the negative X-direction through an imager face  154 .  
         [0031]     A LCOS imager  156  is located opposite of imager face  154  to receive the s-polarized green light. In one embodiment, LCOS imager  156  is mounted on imager face  154 . LCOS image  156  reflects the s-polarized green light and modulates part of the s-polarized green light to generate a green image having p-polarized green light. The green image travels in the positive X-direction back towards PBS  148 . Polarizing surface  152  of PBS  148  passes the green image having the p-polarized green light to an input face  160  of color combiner  128 . In one embodiment, PBS  148  is mounted on input face  160 . Note that other types of imagers may be used in place of LCOS imager  156 .  
         [0032]     Color combiner  128  has a dichroic coating on a diagonal face  162  that reflects red light and passes blue and green lights, and a dichroic coating on a diagonal face  164  that reflects blue light and passes red and green lights. The red image from imager  124  reflects from diagonal face  162  and leaves through an exit face  166 . The blue image from imager  144  reflects from diagonal face  164  and leaves through exit face  166 . The green image from imager  156  passes through diagonal faces  162  and  164  and leaves through exit face  166 . At exit face  166 , the red, green, and blue images merge to form a single image with the appropriate colors. The single image then travels from color combiner  128  to a projection lens  168 . Note that other color combiners may be used in place of X-cube color combiner  128 . In one embodiment, PBS  118 , PBS  136 , PBS  148 , and X-cube color combiner  128  are the Vikuiti Optical Core from  3 M Optical System Division of St. Paul, Minn.  
         [0033]      FIG. 6  illustrates a flowchart for a method  600  to align the color lights to imagers  124   144 , and  156  during the manufacturing process.  
         [0034]     In step  602 , imagers  124 ,  144 , and  156  are connected to a pattern generator to project a white image on the screen and light source  102  is powered up.  
         [0035]     In step  604 , the signals for blue imager  144  and green imager  156  are turned off and the location of light pipe  104  is adjusted along the X-direction to project a uniform and bright red image with sharp edges on the screen (i.e., to focus the red image). In one embodiment, the uniformity and brightness of the red image is measured by a light meter at  9  or  13  different points.  
         [0036]     In step  605 , the location of focusing lens  108  is adjusted along the Y and the Z-directions to move the red image to a specified area defined by the shadow mask of the resulting display.  
         [0037]     In step  606 , the signal for red imager  124  is turned off and the signal for green imager  156  is turned on to project a green image on the screen. Turning mirror  130  is adjusted along the X, Y, and Z-directions and about the X and Y-directions to (1) project a uniform and bright green image with sharp edges on the screen (i.e., to focus the green image), and (2) place the green image to the specified area defined by the shadow mask of the resulting display (i.e., to provide a rectangular shape into the specified area). In one embodiment, the uniformity and brightness of the green image is measured by a light meter at 9 or 13 different points.  
         [0038]     In step  608 , the signal for blue imager  144  is turned on to project a blue image on the screen along with the green image. Any misalignment between the blue and the green images appears visually as a blue light and a green light at the top and the bottom of the combined image, or vice versa. Dichroic mirror  134  is adjusted about the Y-direction until the blue and the green images are aligned. Note that the uniformity and brightness of the blue image are not measured because they should be the same as the uniformity and brightness of the green image, which were adjusted with turning mirror  130  in step  606 .  
         [0039]     In step  610 , the signal for red imager  124  is turned on to project the red image on the screen along with the green and the blue images. At this point, one of three types of misalignment occurs. In a first type of misalignment, a cyan light (a mixture of green and blue lights) appears at two of the edges of a white image. Focusing lens  108  is adjusted along the Y and the Z-directions until a fully white image appears. In a second type of misalignment, a magenta light (a mixture of red and blue lights) appears around the edges of a white image. Turning mirror  130  is adjusted along the Z-direction until a fully white image appears. In a third type of misalignment, a cyan light appears around the edges of a white image. Light pipe  104  is adjusted along the X-direction until a fully white image appears.  
         [0040]     In step  612 , it is determined if the red, the green, and the blue images are aligned within an acceptable tolerance. If the red, the green, and the blue images are not aligned within the acceptable tolerance, then method  600  loops back to any of the above steps from step  604  to  610  to further adjust the alignment of the components. From experience, only further adjustments to turning mirror  130  and focusing lens  108  are needed to align the images within the acceptable tolerance. Step  612  is followed by step  614  if the images are aligned within the acceptable tolerance.  
         [0041]     In step  614 , the locations and positions of light pipe  104 , focusing lens  108 , turning mirror  130 , and dichroic mirror  134  are fixed.  
         [0042]     Various other adaptations and combinations of features of the embodiments disclosed are within the scope of the invention. Numerous embodiments are encompassed by the following claims.