Abstract:
A dual lamp coupling system is provided using a single equilateral 60 degree triangle prism in front of the integrator rod to homogenize the focused light from two lamps, with increased projection brightness. According to one embodiment, the equilateral 60 degree triangular prism is integrated into the end of the rod.

Description:
FIELD 
     The following is directed in general to flat panel display systems, and more particularly to an improved dual lamp coupling for optical integrators used with DMDs and other display related illumination systems. 
     BACKGROUND 
     Optical integrator rods are well known components used primarily in illumination systems for electronic projectors. An optical integrator rod is a hollow or solid internally reflective “light pipe” that uses multiple reflections of a focused light source to obtain homogenization of round or irregular patterns of illumination and convert them into a uniform rectangular pattern. This pattern can be imaged onto a panel such as an LCD (Liquid Crystal Display) or DMD (Digital Micromirror Device) by a relay lens system, and then projected to a screen. Thus, the optical integrator rod is used to improve uniformity and efficiently match the aspect ratio of the illumination source to the panel. 
     There are two basic types of reflective integrators: a “tunnel” type made of four mirrors, and a solid glass integrator or “solid rod integrator”. This latter type is more efficient than the former since it works on lossless multiple reflections using TIR (the Total Internal Reflection) of the glass rod. 
     Traditionally, for a dual lamp projection system separate integrators have been used for each lamp. Light from each lamp is focused orthogonally onto the input face of the associated integrator rod, and collected at the output face thereof for transmission to the relay lens. Examples of prior systems are disclosed in U.S. Pat. No. 6,196,699 (Stanton), U.S. Pat. No. 6,341,876 (Moss et al), U.S. Pat. No. 6,527,420 (Chuang), U.S. Pat. No. 6,857,761 (Chang), U.S. Pat. No. 6,488,379 (Kane). 
     The inventor has recognized the desirability of replacing separate integrator rods for each lamp with a single rod, in order to benefit from advantages such as simple mounting, simple alignment, less coupling loss, lower cost since there is no need to provide a mirror coating (only AR coating is required), and eliminated risk of high power damage on the mirror coating. 
     SUMMARY 
     According to an aspect of this specification, a dual lamp coupling system is provided using a single equilateral 60 degree triangular prism in front of the integrator rod to homogenize the focused light from two lamps and match the aspect ratio of the lamps to an imaging panel. According to one embodiment, the equilateral 60 degree triangular prism is integrated into the end of the rod. 
     Additional aspects and advantages will be apparent to a person of ordinary skill in the art, residing in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A detailed description of the preferred embodiment is set forth in detail below, with reference to the following drawings, in which: 
         FIG. 1  is schematic representation of a dual lamp coupling for optical integrators, according one embodiment of the invention; 
         FIG. 2  is a plan view of the dual lamp coupling shown in  FIG. 1 , depicting the reflection of light rays from dual lamps; and 
         FIG. 3  is a perspective view of a dual lamp coupling according to an alternative embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In  FIGS. 1 and 2 , a 60 degree triangular prism  1  is mounted on its non-illuminated sides so as to couple light rays  2 A and  2 B from lamps  3 A and  3 B, respectively, to an integrator rod  5 . Due to the geometry of the prism  1 , the angle of incidence of the light rays  2 A and  2 B is perpendicular at the input face  6 A and exit face  6 B of the prism  1 , thereby preserving the F-number of the light source, minimizing light loss due to reflection and maximizing the total cross-sectional area of light collection. In a successful implementation of the invention, the two lamps  3 A and  3 B were Gen 3 420W Cermax lamps manufactured by Perkin-Elmer, although any appropriately designed lamps may be used. 
     The light collection efficiency for the arrangement of  FIGS. 1 and 2  has been simulated and compared with a single lamp configuration. Specifically, 9998 light rays were launched from a 420 W Gen 3 Cermax lamp and were focused onto the input face of a single 12×9 mm integrator rod (not shown), resulting in a total of 9534 rays being collected at the input rod face (i.e. a 95% collection efficiency). The dual lamp coupling configuration of  FIGS. 1 and 2  was then tested by launching 9998×2=19996 rays from a 420 W Gen 3 Cermax lamp and focusing the rays onto the input faces  6 A of the prism  1 , resulting in a total of 16354 rays being collected at the input rod face  6 B (i.e. a 82% collection efficiency). However, the coupling efficiency when compared with the single lamp system=16354/9534=1.715 (˜1.72×). Similarly, for a 10×7.5 mm rod  5 , the results were 9089 rays collected for the single lamp configuration (i.e. a 91% collection efficiency) versus 15022 rays collected for the dual lamp coupling (i.e. a 75% collection efficiency, but when compared to the single lamp system=15022/9089=1.653 (˜1.65x)). 
     The coupling efficiencies of both dual lamp and single lamp system are tabulated in Table 1. 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Integrator Input 
                 Integrator Input 
               
               
                   
                 Rays Launched 
                 (12 × 9 mm) 
                 (10 × 7.5 mm) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 SINGLE LAMP 
                  9998 
                 9534 
                 9089 
               
               
                 DUAL LAMP 
                 19996 
                 16354 
                 15022 
               
               
                 Coupling Efficiency 
                 — 
                 1.715 
                 1.653 
               
               
                   
               
             
          
         
       
     
     As can be seen readily from the foregoing, the dual lamp coupling arrangement of the present invention results in better than 50% increase in light collection efficiency at the integrator rod  5  when compared to prior art single lamp configurations. 
     A person skilled in the art, having read this description of the preferred embodiment, may conceive of variations and alternative embodiments. For example, as shown in  FIG. 3 , the 60 degree triangular prism  1 ′ can be integrated into the integrator rod  5 ′ as one single piece. This embodiment has the advantage of reducing reflection loss from the bottom surface of the prism and the front face of the integrator rod  5 ′, although there is less flexibility in terms of the angular orientation of the prism  1 ′ with respect to the integrator rod  5 ′ when compared to the embodiment of  FIGS. 1 and 2  (where the integrator rod  5  may be rotated relative to the prism  1 ). Also, the alternative embodiment may be more costly since the integrated rod and prism require design customization. Also, with appropriate modification of the angle of incidence of light, other internal angles of prism may be used for dual lamp coupling than the equilateral 60 degree triangular prism of the preferred embodiment. 
     All such variations and alternative embodiments are believed to be within the ambit of the claims appended hereto.