Abstract:
An assembly including a first lens having a first surface and a second surface, the first surface being a first convex surface, a second lens having a third surface and a fourth surface, the third surface adhered to the second surface, a third lens having a fifth surface and a sixth surface, the fifth surface adhered to the fourth surface, and a beamsplitter having a seventh surface adhered to the sixth surface is provided.

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 an assembly including a first lens having a first surface and a second surface, the first surface being a first convex surface, a second lens having a third surface and a fourth surface, the third surface adhered to the second surface, a third lens having a fifth surface and a sixth surface, the fifth surface adhered to the fourth surface, and a beamsplitter having a seventh surface adhered to the sixth surface. 
     
     
       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. 2A  is a schematic diagram illustrating an offset digital projection system with a fold mirror according to one embodiment of the present invention. 
           [0006]      FIG. 2B  is a schematic diagram illustrating an offset digital projection system with a fold mirror according to one embodiment of the present invention. 
           [0007]      FIG. 3A  is a schematic diagram illustrating a coupling lens according to one embodiment of the present invention. 
           [0008]      FIG. 3B  is a schematic diagram illustrating a coupling lens according to one embodiment of the present invention. 
           [0009]      FIG. 3C  is a schematic diagram illustrating a coupling lens according to one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    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. 
         [0011]    As described herein, a coupling lens is provided for a digital projection system with common path projection and illumination optics. The coupling lens operates to minimize the amount of stray light in the projection system to increase the full on and full off contrast of the system. To do so, the coupling lens is configured to maximize a distance between the stop of the system and the surface of coupling lens that is nearest to the aperture stop by cementing together a group of lenses that form the coupling lens. The surface of the coupling lens that receives the illumination beam forms a relatively steep surface with respect to the illumination beam to reduce the Fresnel reflections that enter the projection path of the projection system. Further, the indices of refraction of the lenses and cements may be optimized to minimize ghosting in the system. 
         [0012]      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 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 at least one modulating element (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 illuminated with minimum overfill. Coupling lens  110  directs the illumination beam onto modulation device  114  at a non-zero angle of incidence such that the illumination beam is telecentric. Coupling lens  110  is substantially centered with respect to modulation device  114 . 
         [0013]    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  telecentrically directs the imaging beam from modulation device  114  through a projection lens  120  along a projection path  118  such 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 (not shown). Projection lens  120  images modulation device  114  through coupling lens  110  onto the screen or other display surface used for final display. 
         [0014]    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 aperture stop plane  124  of the system such that the imaging beam is spatially separated from the illumination beam at aperture stop plane  124 . Accordingly, illumination path  108  is effectively separated from projection path  118 . In the embodiment of  FIG. 1 , coupling lens  110  includes all optical elements between aperture stop plane  124  and modulation device  114 . 
         [0015]    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. 
         [0016]      FIG. 2A  is a schematic diagram illustrating an embodiment  10 A of offset digital projection system  10  with a fold mirror  202 . In projection system  10 A, illumination source  102  generates and emits the illumination beam to the illumination relay  106  along an optical path  104 . Illumination relay  106  provides the illumination beam to fold mirror  202 . 
         [0017]    Fold mirror  202  reflects the illumination beam from illumination relay  106  through coupling lens  110  along an illumination path  204  such that an optical axis of illumination path  204  of the illumination beam is parallel or substantially parallel to optical axis  100  of modulation device  114  between fold mirror  202  and coupling lens  110 . In the embodiment shown in  FIG. 2 , fold mirror  202  reflects the illumination beam at an angle of approximately ninety degrees between the optical axis of illumination relay  106  and optical axis  100 . In other embodiments, fold mirror  202  may be positioned differently to reflect the illumination beam at any non-zero angle between the optical axis of illumination relay  106  and optical axis  100 . 
         [0018]    Coupling lens  110  refracts and focuses the illumination beam onto modulation device  114  through a beamsplitter  206  along optical path  112 . Beamsplitter  206  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  206 . Beamsplitter  206  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  206  may be omitted in embodiments where modulation device  114  includes a single modulator. Coupling lens  110  refracts illumination beam  202  onto modulation device  114  at a non-zero angle of incidence. 
         [0019]    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 beamsplitter  206  and into coupling lens  110  along optical path  116 . Coupling lens  110  refracts the imaging beam from modulation device  114  through projection lens  120  such that the imaging beam travels along an optical axis of optical path  118  which is parallel or substantially parallel to normal  100  to plane  101  of modulation device  114  and an optical axis of illumination path  204  of the illumination beam between coupling lens  110  and pupil plane  124 . Projection lens  120  focuses and may zoom the imaging beam along optical path  122  to cause still or video images to be formed on a screen or other display surface. 
         [0020]    In projection system  10 A, illumination relay  106 , coupling lens  110 , and projection lens  120  are situated so as to minimize the overlap of the illumination beam and the imaging beam along illumination path  204  and optical path  118 . In particular, the illumination beam and the imaging beam each intersect different areas of aperture stop plane  124  of the system such that the imaging beam is spatially separated from the illumination beam at aperture stop plane  124 . Accordingly, the illumination path is effectively separated from the projection path. 
         [0021]      FIG. 2B  is a schematic diagram illustrating an embodiment  10 B of offset digital projection system  10  with a fold mirror  212 . In projection system  10 B, illumination source  102  generates and emits an illumination beam to illumination relay  106  along optical path  104 . Illumination relay  106  integrates 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 . 
         [0022]    Coupling lens  110 , beamsplitter  206 , and modulation device  114  operate as described with reference to  FIG. 2A  above. Coupling lens  110  refracts the imaging beam from modulation device  114  to fold mirror  212  such that the imaging beam travels along an optical axis of optical path  118  that is parallel or substantially parallel to normal  100  to plane  101  of modulation device  114  and an optical axis of optical path  108  of the illumination beam. 
         [0023]    Fold mirror  212  reflects the imaging beam from coupling lens  110  into projection lens  120  along an optical path  214 . In the embodiment shown in  FIG. 2B , fold mirror  212  reflects the imaging beam at an angle of approximately ninety degrees between normal  100  and an optical axis of optical path  214 . In other embodiments, fold mirror  212  may be positioned differently to reflect the imaging beam at any non-zero angle between normal  100  and the optical axis of optical path  214 . Projection lens  120  focuses and may zoom the imaging beam from fold mirror  212  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 , 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 aperture stop plane  124  of the system such that the imaging beam is spatially separated from the illumination beam at aperture stop plane  124 . Accordingly, illumination path  108  is effectively separated from projection path  118 . 
         [0025]    In other embodiments, fold mirrors  202  ( FIG. 2A) and 212  ( FIG. 2B ) may replaced with other reflective surfaces. In addition, a system may include fold mirrors in both the illumination and projection paths in other embodiments. 
         [0026]    Coupling lens  110  may be configured according to embodiments  110 A,  110 B, and  110 C of  FIGS. 3A ,  3 B, and  3 C, respectively, to minimize the amount of stray light that reflects off of coupling lens  110  from the illumination path into the projection path of projection system  10 . Embodiments  110 A,  110 B, and  110 C of coupling lens  110  are also configured to maximize a distance between aperture stop plane  124  and the surface of coupling lens that is nearest to aperture stop plane  124  by cementing combinations of lenses together. Embodiments  110 A,  110 B, and  110 C are further configured with a relatively steep surface lens that is nearest to pupil plane  124 . 
         [0027]      FIG. 3A  is a schematic diagram illustrating embodiment  110 A of coupling lens  110 . Coupling lens  110 A includes lenses  302 ,  304 , and  306  where lens  306  is adhered to a planar surface  206 A of beamsplitter  206 . Beamsplitter  206  is adhered to modulation device  114 . 
         [0028]    Lens  302  is a biconvex lens with a spherical convex surface  302 A and a spherical convex surface  302 B. Lens  302  receives the illumination beam along Illumination path  108  and refracts the illumination beam into lens  304 . Surface  302 A forms a relatively steep surface with respect to the illumination beam to minimize the amount of light from the illumination beam that reflects off of surface  302 A an into projections lens  120 . Lens  304  is a biconcave lens with a spherical concave surface  304 A and a spherical concave surface  304 B. Lens  304  receives the illumination beam from lens  302  and refracts the illumination beam into lens  306 . Lens  306  is a piano-convex lens with a spherical convex surface  306 A and a planar surface  306 B. Lens  306  receives the illumination beam from lens  304  and refracts the illumination beam into beamsplitter  206 . 
         [0029]    Beamsplitter  206  splits the illumination beam into separate components and refracts each component onto a suitable modulator of modulation device  114 . Each modulator modulates the illumination beam from beamsplitter  206  according to an input signal, e.g., a computer or video input signal, (not shown) to form an imaging beam. The imaging beams are reflected from the modulators and refracted by beamsplitter  206  to combine into a single imaging beam. Lens  306  receives the combined imaging beam and refracts the imaging beam into lens  304 . Lens  304  receives the imaging beam from lens  306  and refracts the imaging beam into lens  302 . Lens  302  receives the imaging beam from lens  304  and refracts the imaging beam along projection path  118 . 
         [0030]    The cements that adhere lenses  302 ,  304 ,  306 , and beamsplitter  206  are chosen to minimize Fresnel reflections and increase the full on and full off contrast of projection system  10 . In particular, the cements are chosen to match the indices of refraction of lenses with equal indices of refraction and approximate the average of the indices of refraction of lenses with unequal indices of refraction. 
         [0031]    Surfaces  302 B and  304 A have an equal or approximately equal radius of curvature and are adhered together at an interface  312  using cement that has an index of refraction that is between an index of refraction of lens  302  and an index of refraction of lens  304 . Similarly, surfaces  304 B and  306 A have an equal or approximately equal radius of curvature and are adhered together at an interface  314  using cement that has an index of refraction that is between an index of refraction of lens  304  and an index of refraction of lens  306 . Further, surfaces  306 B and  206 A are planar or substantially planar and are adhered together at an interface  316  using cement that has an index of refraction that is equal or approximately equal to the indices of refraction of lens  306  and beamsplitter  206 . 
         [0032]    In one embodiment, lenses  302  and  306  and beamsplitter  206  have equal or approximately equal indices of refraction, and lens  304  has an index of refraction that is higher than the indices of refraction of lenses  302  and  306  and beamsplitter  206 . In other embodiments, the indices of refraction of lenses  302 ,  304 , and  306  and beamsplitter  206  may have other relationships. 
         [0033]    In one embodiment, coupling lens  110 A follows the lens prescription of Table 1. In another embodiment, coupling lens  110 A follows the lens prescription of Table 2. In other embodiments, coupling lens  110 A follows other lens prescriptions. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 RADIUS OF 
                 THICKNESS 
                 INDEX OF 
               
               
                 SURFACE 
                 CURVATURE 
                 (mm) 
                 REFRACTION 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 302A 
                 26.659057 
                 8.471674 
                 1.51680 
               
               
                 302B/304A 
                 −101.904755 
                 4.499952 
                 1.61293 
               
               
                 304B/306A 
                 15.531690 
                 9.609135 
                 1.51680 
               
               
                 306B/206A 
                 Infinity 
                 31.257110 
                 1.51680 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                 RADIUS OF 
                 THICKNESS 
                 INDEX OF 
               
               
                 SURFACE 
                 CURVATURE 
                 (mm) 
                 REFRACTION 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 302A 
                 25.479300 
                 9.63730 
                 1.51680 
               
               
                 302B/304A 
                 −100.001100 
                 4 
                 1.61293 
               
               
                 304B/306A 
                 15.376700 
                 11.173270 
                 1.51680 
               
               
                 306B/206A 
                 Infinity 
                 31.260000 
                 1.51680 
               
               
                   
               
             
          
         
       
     
         [0034]      FIG. 3B  is a schematic diagram illustrating embodiment  110 B of coupling lens  110 . Coupling lens  110 B includes lenses  322 ,  324 , and  326  where lens  326  is adhered to planar surface  206 A of beamsplitter  206 . Beamsplitter  206  is adhered to modulation device  114 . 
         [0035]    Lens  322  is a convex-concave lens with an even aspherical convex surface  322 A and a spherical concave surface  322 B. Lens  322  receives the illumination beam along Illumination path  108  and refracts the illumination beam into lens  324 . Surface  322 A forms a relatively steep surface with respect to the illumination beam to minimize the amount of light from the illumination beam that reflects off of surface  322 A an into projections lens  120 . Lens  324  is a convex-concave lens with a spherical convex surface  324 A and a spherical concave surface  324 B. Lens  324  receives the illumination beam from lens  322  and refracts the illumination beam into lens  326 . Lens  326  is a plano-convex lens with a spherical convex surface  326 A and a planar surface  326 B. Lens  326  receives the illumination beam from lens  324  and refracts the illumination beam into beamsplitter  206 . 
         [0036]    Beamsplitter  206  splits the illumination beam into separate components and refracts each component onto a suitable modulator of modulation device  114 . Each modulator modulates the illumination beam from beamsplitter  206  according to an input signal, e.g., a computer or video input signal, (not shown) to form an imaging beam. The imaging beams are reflected from the modulators and refracted by beamsplitter  206  to combine into a single imaging beam. Lens  326  receives the combined imaging beam and refracts the imaging beam into lens  324 . Lens  324  receives the imaging beam from lens  326  and refracts the imaging beam into lens  322 . Lens  322  receives the imaging beam from lens  324  and refracts the imaging beam along projection path  118 . 
         [0037]    The cements that adhere lenses  322 ,  324 ,  326 , and beamsplitter  206  are chosen to minimize Fresnel reflections and increase the full on and full off contrast of projection system  10 . In particular, the cements are chosen to match the indices of refraction of lenses with equal indices of refraction and approximate the average of the indices of refraction of lenses with unequal indices of refraction. 
         [0038]    Surfaces  322 B and  324 A have an equal or approximately equal radius of curvature and are adhered together at an interface  332  using cement that has an index of refraction that is between an index of refraction of lens  322  and an index of refraction of lens  324 . Similarly, surfaces  324 B and  326 A have an equal or approximately equal radius of curvature and are adhered together at an interface  334  using cement that has an index of refraction that is between an index of refraction of lens  324  and an index of refraction of lens  326 . Further, surfaces  326 B and  206 A are planar or substantially planar and are adhered together at an interface  336  using cement that has an index of refraction that is equal or approximately equal to the indices of refraction of lens  326  and beamsplitter  206 . 
         [0039]    In one embodiment, lenses  322  and  326  and beamsplitter  206  have equal or approximately equal indices of refraction, and lens  324  has an index of refraction that is higher than the indices of refraction of lenses  322  and  326  and beamsplitter  206 . In other embodiments, the indices of refraction of lenses  322 ,  324 , and  326  and beamsplitter  206  may have other relationships. 
         [0040]    In one embodiment, coupling lens  110 B follows the lens prescription of Table 3. In other embodiments, coupling lens  110 B follows other lens prescriptions. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
                 RADIUS OF 
                 THICKNESS 
                 INDEX OF 
               
               
                 SURFACE 
                 CURVATURE 
                 (mm) 
                 REFRACTION 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 322A 
                 Aspherical 
                 6.070206 
                 1.43875 
               
               
                 322B/324A 
                 116.822626 
                 3.993753 
                 1.688.93 
               
               
                 324B/326A 
                 15.340970 
                 31.911897 
                 1.51680 
               
               
                 326B/206A 
                 Infinity 
                   
                 1.51680 
               
               
                   
               
             
          
         
       
     
         [0041]    In Table 3, the thickness shown for lens  326  includes the thickness of beamsplitter  206 . 
         [0042]    Surface  322 A of lens  322  further follows the lens prescription of Table 4. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 BASE RADIUS OF 
                   
               
               
                   
                 CURVATURE 
                 17.197986 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                  4 TH  ORDER TERM 
                 −1.193542E−05 
               
               
                   
                  6 TH  ORDER TERM 
                 1.502243E−08 
               
               
                   
                  8 TH  ORDER TERM 
                 −6.987755E−10 
               
               
                   
                 10 TH  ORDER TERM 
                 3.801264E−12 
               
               
                   
                 12 TH  ORDER TERM 
                 −9.793144E−15 
               
               
                   
                 14 TH  ORDER TERM 
                 0.00 
               
               
                   
                   
               
             
          
         
       
     
         [0043]      FIG. 3C  is a schematic diagram illustrating embodiment  110 C of coupling lens  110 . Coupling lens  110 C includes lenses  342 ,  344 , and  346  where lens  346  is adhered to planar surface  206 A of beamsplitter  206 . Beamsplitter  206  is adhered to modulation device  114 . 
         [0044]    Lens  342  is a convex-concave lens with an aspherical convex surface  342 A and a spherical concave surface  342 B. Lens  342  receives the illumination beam along Illumination path  108  and refracts the illumination beam into lens  344 . Surface  342 A forms a relatively steep surface with respect to the illumination beam to minimize the amount of light from the illumination beam that reflects off of surface  342 A an into projections lens  120 . Lens  344  is a convex-concave lens with a spherical convex surface  324 A and a spherical concave surface  324 B. Lens  344  receives the illumination beam from lens  342  and refracts the illumination beam into lens  346 . Lens  346  is a plano-convex lens with a spherical convex surface  346 A and a planar surface  346 B. Lens  346  receives the illumination beam from lens  344  and refracts the illumination beam into beamsplitter  206 . 
         [0045]    Beamsplitter  206  splits the illumination beam into separate components and refracts each component onto a suitable modulator of modulation device  114 . Each modulator modulates the illumination beam from beamsplitter  206  according to an input signal, e.g., a computer or video input signal, (not shown) to form an imaging beam. The imaging beams are reflected from the modulators and refracted by beamsplitter  206  to combine into a single imaging beam. Lens  346  receives the combined imaging beam and refracts the imaging beam into lens  344 . Lens  344  receives the imaging beam from lens  346  and refracts the imaging beam into lens  342 . Lens  342  receives the imaging beam from lens  344  and refracts the imaging beam along projection path  118 . 
         [0046]    The cements that adhere lenses  342 ,  344 ,  346 , and beamsplitter  206  are chosen to minimize Fresnel reflections and increase the full on and full off contrast of projection system  10 . In particular, the cements are chosen to match the indices of refraction of lenses with equal indices of refraction and approximate the average of the indices of refraction of lenses with unequal indices of refraction. 
         [0047]    Surfaces  342 B and  344 A have an equal or approximately equal radius of curvature and are adhered together at an interface  352  using cement that has an index of refraction that is between an index of refraction of lens  342  and an index of refraction of lens  344 . Similarly, surfaces  344 B and  346 A have an equal or approximately equal radius of curvature and are adhered together at an interface  354  using cement that has an index of refraction that is between an index of refraction of lens  344  and an index of refraction of lens  346 . Further, surfaces  346 B and  206 A are planar or substantially planar and are adhered together at an interface  356  using cement that has an index of refraction that is equal or approximately equal to the indices of refraction of lens  346  and beamsplitter  206 . 
         [0048]    In one embodiment, lenses  342  and  346  and beamsplitter  206  have equal or approximately equal indices of refraction, and lens  344  has an index of refraction that is higher than the indices of refraction of lenses  342  and  346  and beamsplitter  206 . In other embodiments, the indices of refraction of lenses  342 ,  344 , and  346  and beamsplitter  206  may have other relationships. 
         [0049]    In one embodiment, coupling lens  110 C follows the lens prescription of Table 5. In other embodiments, coupling lens  110 C follows other lens prescriptions. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 5 
               
               
                   
               
               
                   
                 RADIUS OF 
                 THICKNESS 
                 INDEX OF 
               
               
                 SURFACE 
                 CURVATURE 
                 (mm) 
                 REFRACTION 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 342A 
                 Aspherical 
                 7.5 
                 1.46008 
               
               
                 342B/344A 
                 44.4846 
                 3.7 
                 1.78472 
               
               
                 344B/346A 
                 16.01 
                 8 
                 1.46008 
               
               
                 346B/206A 
                 Infinity 
                   
                 1.46008 
               
               
                   
               
             
          
         
       
     
         [0050]    With the lens prescription of Table 5, beamsplitter  206  may have any suitable thickness. 
         [0051]    Surface  342 A of lens  342  further follows the lens prescription of Table 6. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 6 
               
               
                   
                   
               
               
                   
                 BASE RADIUS OF 
                   
               
               
                   
                 CURVATURE 
                 17.4502 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                  4 TH  ORDER TERM 
                 −1.30E−05 
               
               
                   
                  6 TH  ORDER TERM 
                 3.20E−08 
               
               
                   
                  8 TH  ORDER TERM 
                 −7.70E−10 
               
               
                   
                 10 TH  ORDER TERM 
                 3.80E−12 
               
               
                   
                 12 TH  ORDER TERM 
                 −8.60E−15 
               
               
                   
                 14 TH  ORDER TERM 
                 −9.80E−19 
               
               
                   
                   
               
             
          
         
       
     
         [0052]    Embodiments  110 A,  110 B, and  110 C may advantageously minimize the amount of stray light that is reflected into the projection path of projection system  10  by maximizing the distance between pupil plane  124  and the surface of coupling lens  110  that is nearest to aperture stop plane  124  (i.e., surface  302 A, surface  322 A, and surface  342 A). The distance is maximized by cementing the lenses in each embodiment together. In addition, the curvatures of the lenses in each embodiment  110 A,  110 B, and  110 C forms a relatively steep surface with respect to the illumination beam to reduce the Fresnel reflections that enter the projection path. As a result, the full on and full off contrast of projection system  10  may be increased. Further, the indices of refraction of the lenses and cements may be optimized as described above to minimize ghosting in the system. 
         [0053]    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. 
         [0054]    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.