Polarization recovery system for protection display

Abstract

A waveguide polarization recovery system both polarizes the input light energy for use with an LCD imager and converts the polarity of unusable light energy to add to the illumination of the LCD imager. The compact polarization recovery waveguide system generally includes: (1) an input waveguide that provides non-polarized light energy into the system; (2) an output waveguide that receives polarized light energy from the system; (3) a polarized beam splitter that received the light energy from the input waveguide and transmits light energy of a first polarization type and reflects light energy of a second polarization type, and (4) a wave plate that modifies the polarization of either the transmitted or reflected light energy. The polarization recovery system also generally includes one or more mirrors that are positioned as need to direct the transmitted and the reflected light energy to the output waveguide. The input and output waveguides may be shaped as needed by the projection system. For example, either one or both of the input and output waveguides may be tapered as needed to produce a desired image. In the waveguide polarization recovery system, the input and output waveguides are configured to have either an either a substantially parallel or a substantially perpendicular orientation. In another embodiment, the waveguide polarization recovery system further includes has one or more “gaps” of optically clear material positioned between the optical components to encourage the occurrence to total internal reflection that minimizes the loss of the optical energy by the system.

1 . A light guide comprising: 
 first, second and third guide sections; and    a light coupling element between the light guide sections;    the light guide sections each having an entrance aperture, an exit aperture and at least first and second guide walls defining a light guide direction;    the light coupling element being composed of an optically transparent material having first and second entrance faces each with a TIR surface, an exit face with a TIR surface, and a reflecting face;    the light coupling element also having an internal polarizing surface for reflecting light of a predetermined polarization state.    
     
     
         2 . The light guide of  claim 1  in which the cross sections of the light guide sections have the cross sectional shape of an even-numbered polygon.  
     
     
         3 . The light guide of  claim 1  in which at least the first light guide section is solid element of an optically transparent material, and the entrance face of light coupling element adjacent to the exit aperture of the solid first light guide section is spaced a distance apart from the exit aperture of light guide section, to form a space between the entrance face of light coupling element and the exit aperture of the solid light guide section.  
     
     
         4 . The light guide of  claim 3  in which the space is filled with air.  
     
     
         5 . The light guide of  claim 3  in which the space is filled with an optically transparent material having an index of refraction less than that of the material of the light coupling element.  
     
     
         6 . The light guide of  claim 3  in which the distance d between the entrance face of light coupling element and the exit aperture of the solid light guide section is substantially the same across the width of the space.  
     
     
         7 . The light guide of  claim 1  in which at least the first light guide section is a hollow conduit having a guide wall with an interior reflective surface.  
     
     
         8 . The light guide of  claim 3  in which the space is filled with a low index epoxy.  
     
     
         9 . The light guide of  claim 1 , where one of the light guide sections is a triangular prism.