Polarization gratings in mesogenic films

Abstract

A polarizer including a polarization grating comprising a polarization sensitive photo-alignment layer and a liquid crystal composition arranged on said photo-alignment layer. An alignment pattern, corresponding to the polarization pattern of a hologram, is recorded in the photo-alignment layer, and the liquid crystal composition is aligned on the photo-alignment layer.

1 - 22 . (canceled) 
     
     
         23 . A two-dimensional polarization grating comprising a polarization sensitive photo-alignment layer and a liquid crystal composition arranged on said alignment layer, wherein an anisotropic alignment pattern corresponding to a polarization hologram is arranged in said photo-alignment layer and said liquid crystal composition is aligned by said alignment pattern, and wherein the liquid crystal composition has a layer thickness d which is determined by the following formula
     d≦d   max =Λ/2
   where d is the thickness of the layer and Λ is the pitch of the polarization grating.   
     
     
         24 . The polarization grating according to  claim 23 , wherein the alignment direction of said anisotropic alignment pattern is periodic along at least one line in the plane of the alignment layer. 
     
     
         25 . The polarization grating according to  claim 24 , wherein the alignment direction exhibits a periodic variation, which over one period corresponds to the polarization direction variation along a circle on the Poincarésphere. 
     
     
         26 . The polarization grating according to  claim 24 , wherein said alignment direction variation corresponds to a polarization direction variation in linear polarization. 
     
     
         27 . The polarization grating according to  claim 23 , wherein said liquid crystal composition comprises polymerizable mesogens. 
     
     
         28 . The polarization grating according to  claim 23 , wherein said liquid crystal composition is at least partly polymerized. 
     
     
         29 . The polarization grating according to  claim 23 , comprising at least a first and a second liquid crystal composition, wherein said first liquid crystal composition is arranged on and aligned by said alignment layer and at least partly polymerized, and wherein said second liquid crystal composition is arranged on and aligned by said first liquid crystal composition. 
     
     
         30 . The polarization grating according to  claim 29 , wherein both liquid crystal compositions have a layer thickness d which is determined by the following formula
     d≦d   max =Λ/2
   where d is the thickness of the layer and Λ is the pitch of the polarization grating.   
     
     
         31 . The polarization grating according to  claim 29 , wherein the total thickness d total  of both liquid crystal compositions is determined by the following formula
     d   total >Λ/2.
   
     
     
         32 . The polarization grating according to  claim 23 , comprising two photo-alignment layers being provided with an anisotropic alignment pattern of chemical bonds, said photo-alignment layers sandwiching and aligning said liquid crystal composition. 
     
     
         33 . The polarization grating according to  claim 23 , wherein said liquid crystal composition further comprises a functional compound selected from the group consisting of absorbing dyes, fluorescent dyes, electroluminescent dyes, nano- and micro-particles having anisotropic shape and/or spectral properties, and any combination thereof. 
     
     
         34 . The polarization grating according to  claim 23 , further comprising means for establishing an electric and/or magnetic field in said liquid crystal composition. 
     
     
         35 . A polarization grating, comprising a first polarization grating and a second polarization grating being arranged on said first polarization grating, wherein said first polarization grating exhibits a first optical axis pattern, wherein said second polarization grating exhibits a second optical axis pattern, said second optical axis pattern being rotated in the plane of said grating at an angle in the range of from 30 to 60° towards said first optical axis pattern, and wherein at least one of said first and said second polarization gratings is a two-dimensional polarization grating according to  claim 23 . 
     
     
         36 . The polarization grating according to  claim 29 , wherein a cholesteric liquid crystal composition is arranged between said first liquid crystal composition and said second liquid crystal composition, wherein said cholesteric liquid crystal composition exhibits a twist in the range of 30 to 60°. 
     
     
         37 . The polarization grating according to  claim 32 , comprising a light source and electrode means for applying an electrical field in said polarization grating. 
     
     
         38 . The polarization grating according to  claim 37 , wherein said electrode means is patterned into a plurality of domains, each domain being independently addressable. 
     
     
         39 . The polarization grating according to  claim 37 , comprising a color filter arranged between said light source and said polarization grating. 
     
     
         40 . The polarization grating according to  claim 37 , comprising a means for blocking light that is diffracted by said polarization grating into a diffraction order other than the zeroth diffraction order.