Optical polarizer

Abstract

A reflective polarizer and a dichroic polarizer are combined to provide an improved optical polarizer. The dichroic and reflective polarizers are typically in close proximity to each other, and are preferably bonded together to eliminate the air gap between the polarizers. The combination of the two polarizers provides a high reflectivity of one polarization and high transmission for the perpendicular polarization from the reflective polarizer side of the combined polarizer, and high absorption and transmission for light of orthogonal polarization from the dichroic polarizer side. The combination also reduces iridescence as seen in transmission and when viewed in reflection from the dichroic polarizer side. The increased extinction ratio and low reflectivity of the optical polarizer allows use of a lower extinction ratio dichroic polarizer in applications requiring a given extinction ratio and high transmission.

1 .- 6 . (canceled)  
     
     
         7 . A display, comprising: 
 a liquid crystal display module;    a backlight;    a front display polarizer comprising a broadband reflective polarizer having anisotropic refractive indices such that light having a first polarization state is reflected and light having a second polarization state is transmitted, the reflective polarizer having a viewing side facing away from the liquid crystal display module and an opposing side facing the liquid crystal display module.    
     
     
         8 . A display as recited in claim  1 , further comprising a rear display polarizer disposed between the backlight and the liquid crystal display module.  
     
     
         9 . A display as recited in claim  2 , wherein the rear display polarizer comprises a broadband reflective polarizer having anisotropic refractive indices such that light having a first polarization state is reflected and light having a second polarization state is transmitted.  
     
     
         10 . A display as recited in claim  3 , wherein the rear display polarizer further comprises an absorbing polarizer disposed at the viewing side of the reflective polarizer and being aligned to absorb light of the first polarization and to transmit light of the second polarization.  
     
     
         11 . A display as recited in claim  1 , wherein the front display polarizer further comprises an absorbing polarizer disposed at the viewing side of the reflective polarizer and being aligned to absorb light of the first polarization and to transmit light of the second polarization.  
     
     
         12 . A display as recited in claim  5 , wherein the absorbing polarizer is bonded to the viewing side of the reflective polarizer.  
     
     
         13 . A display as recited in claim  1 , wherein the reflective polarizer comprises polymeric material.  
     
     
         14 . A display as recited in claim  1 , wherein the reflective polarizer comprises a multilayer stack of two different materials.  
     
     
         15 . A display as recited in  claim 8 , wherein the multilayer stack comprises alternating layers of a polymer based on naphthalene dicarboxylic acid and a polymer formed from at least one of the following: naphthalene dicarboxylic acid, isopthalic acid, terephthalic acid, cycloalkane dicarboxylic acids, alkane dicarboxylic acids, ethylene glycol, alkane glycols, cycloalkane glycols, bisphenol A and carbonic acid.  
     
     
         16 . A display as recited in claim  1 , wherein the reflective polarizer exploits constructive interference to reflect light of the first polarization.  
     
     
         17 . A display as recited in claim  1 , wherein the reflective polarizer is a cholesteric reflective polarizer.  
     
     
         18 . A display as recited in  claim 11 , wherein the front display polarizer further comprises an optical retarder.  
     
     
         19 . A display as recited in claim  1 , further comprising an antireflection coating disposed on the reflective polarizer.  
     
     
         20 . A method of increasing brightness of a display comprising a liquid crystal display module and a backlight, the method comprising the step of: 
 disposing a broadband reflective polarizer with a viewing side of the reflective polarizer facing away from the liquid crystal display module and an opposing side of the reflective polarizer facing the liquid crystal display module;    wherein the reflective polarizer has anisotropic refractive indices such that light having a first polarization state is reflected and light having a second polarization state is transmitted and wherein the reflective polarizer returns at least a portion of light of the first polarization supplied by the backlight and passed by the liquid crystal module back into the backlight.    
     
     
         21 . A method as recited in  claim 14 , further comprising disposing between the backlight and the liquid crystal display module an additional broadband reflective polarizer having anisotropic refractive indices such that light having a first polarization state is reflected and light having a second polarization state is transmitted.  
     
     
         22 . A method as recited in  claim 14 , wherein the reflective polarizer comprises a multilayer stack of two different materials.  
     
     
         23 . A method as recited in  claim 16 , wherein the reflective polarizer exploits constructive interference to reflect light of the first polarization.  
     
     
         24 . A method as recited in  claim 16 , wherein the multilayer stack comprises alternating layers of a polymer based on crystalline naphthalene dicarboxylic acid and a copolyester of naphthalene dicarboxylic acid and tetephthalic acid.  
     
     
         25 . A method as recited in  claim 14 , wherein the reflective polarizer is a cholesteric reflective polarizer.  
     
     
         26 . A method as recited in  claim 14 , wherein the display further comprises an antireflection coating disposed on the reflective polarizer.