Polarized light extraction optical element

Abstract

A polarized light extraction optical element is formed by a light-transmitting base material and a polarization separation layer laminated thereonto, this polarization separation layer being a liquid crystal layer made of a cholesteric liquid crystal. The thickness of the liquid crystal layer is smaller than the thickness that would be required to achieve a maximum reflectivity, so that part of one of the right and left circularly polarized light components is reflected with a reflectivity smaller than the maximum reflectivity.

What is claimed is:  
     
         1 . A polarized light extraction optical element comprising: 
 a substrate; and    a polarization separation layer laminated onto to said substrate,    wherein said polarization separation layer has one of two functions, one to separate at least part of non-polarized incident light into two linearly polarized lights, the polarization directions of which are mutually perpendicular, one being reflected, and another being transmitted, and the other to separate at least part of non-polarized incident light into two circularly polarized lights, the rotational directions of which are mutually opposite, one being reflected and another being transmitted,    a thickness of said polarization separation layer is within a range of 10% to 90% of a thickness required to reflect the one polarized light component with a maximum reflectivity,    said polarization separation layer is a birefringent layer of multilayer planar construction comprising at least three laminated layers of birefringent material such that a difference in refractive indices of layers that are mutually adjacent in a thickness direction with respect to one of two linearly polarized light components that have oscillation directions that are mutually perpendicular within the plane of each layer is different than a difference in refractive indices of layers mutually adjacent thereto in said thickness direction with respect to the other linearly polarized light component, and    the number of laminated layers of birefringent material is made smaller than the number required to reflect one of said linearly polarized light components with maximum reflectivity, so that said one linearly polarized light component is reflected with reflectivity smaller than the maximum reflectivity, said other linearly polarized light component being transmitted.    
     
     
         2 . The polarized light extraction optical element according to  claim 1 , wherein it is possible further provide an auxiliary polarization separation layer on said polarization separation layer, said auxiliary polarization separation layer having planar laminated construction of three or more layers of birefringent material, such that a difference in refractive indices of layers that are mutually adjacent in a thickness direction with respect to one of two linearly polarized light components that have oscillation directions that are mutually perpendicular within the plane of each layer is different than a difference in refractive indices of layers mutually adjacent thereto in said thickness direction with respect to said other linearly polarized light component, 
 wherein the number of laminations of said birefringent material in the auxiliary polarization separation layer is made smaller than the number required to reflect one of the other linearly polarized light components with the maximum reflectivity, so said other linearly polarized light component is reflected with a reflectivity that is smaller than the maximum reflectivity, with light of the opposing linear polarization direction being transmitted.    
     
     
         3 . The polarized light extraction optical element according to  claim 1 , wherein the number of birefringent material layers in at least one of the polarization separation layer and the auxiliary polarization separation layer is made 30 to 150.