Optical film with sharpened bandedge

Abstract

The present invention provides reflective films and other optical bodies which exhibit sharp bandedges on one or both sides of the main reflection bands. The optical bodies comprise multilayer stacks M 1 and M 2 , each having first order reflections in a desired part of the spectrum and comprising optical repeating units R 1 and R 2 , respectively. At least one of the optical repeating units R 1 and R 2 varies monotonically in optical thickness along the thickness of the associated multilayer stack.

1 . A reflective film comprising a plurality of optical repeating units having an optical thickness profile that defines a curve, the curve having substantially no discontinuities in its first derivative and shaped so that it, in order, monotonically decreases from an initial optical thickness to a minimum optical thickness, remains substantially constant at the minimum optical thickness, monotonically increases from the minimum optical thickness to a maximum optical thickness, remains substantially constant at the maximum optical thickness, and monotonically decreases from the maximum optical thickness to an end optical thickness, wherein the optical repeating units monotonically increasing from the minimum optical thickness to the maximum optical thickness form a reflection band.  
     
     
         2 . The reflective film of  claim 1 , wherein the reflection band includes visible light.  
     
     
         3 . The reflective film of  claim 1 , wherein the reflection band includes infrared light.  
     
     
         4 . The reflective film of  claim 1 , wherein the reflection band includes ultraviolet light.  
     
     
         5 . The reflective film of  claim 1 , wherein the optical repeating units comprise polymer layers.  
     
     
         6 . The reflective film of  claim 1 , wherein the optical repeating units comprise a plurality of layers.  
     
     
         7 . The reflective film of  claim 5 , wherein at least a portion of the optical repeating units comprise two layers.  
     
     
         8 . The reflective film of  claim 5 , wherein at least a portion of the optical repeating units comprise three layers A, B, and C arranged in an order ABC, the layers having respective indices of refraction n a , n b , and n c  that differ from each other, index n b  being intermediate to indices n a  and n c .  
     
     
         9 . The reflective film of  claim 8 , wherein the three layers are arranged in an order ABCB.