Refractive index modulation modification in a holographic grating

Abstract

Techniques disclosed herein relate to modifying refractive index modulation in a holographic optical element, such as a holographic grating. According to certain embodiments, a holographic optical element or apodized grating includes a polymer layer comprising a first region characterized by a first refractive index and a second region characterized by a second refractive index. The holographic optical element or apodized grating includes a plurality of nanoparticles dispersed in the polymer layer. The nanoparticles have a higher concentration in either the first region or the second region. In some embodiments, the nanoparticles may be configured to increase the refractive index modulation. In some embodiments, the nanoparticles may be configured to apodize the grating by decreasing the refractive index modulation proximate to sides of the grating. The refractive index may be modulated by applying a monomer reservoir buffer layer to the polymer layer, either before or after hologram fabrication.

What is claimed is: 
     
         1 . A holographic grating comprising:
 a polymer matrix comprising:
 a first region characterized by a first refractive index; 
 a second region characterized by a second refractive index, the second refractive index being higher than the first refractive index; and 
   a resin layer disposed on the polymer matrix, the resin layer comprising:
 a support layer; and 
 a first plurality of nanoparticles dispersed in the support layer of the resin layer. 
   
     
     
         2 . The holographic grating of  claim 1 , wherein the nanoparticles are monomers. 
     
     
         3 . The holographic grating of  claim 1 , wherein:
 the polymer matrix further comprises a second plurality of nanoparticles;   the second plurality of nanoparticles have a higher concentration in the second region than in the first region; and   the second plurality of nanoparticles have a third refractive index that is higher than the second refractive index.   
     
     
         4 . The holographic grating of  claim 1 , wherein:
 the polymer matrix further comprises a second plurality of nanoparticles;   the second plurality of nanoparticles have a higher concentration in the first region than in the second region; and   the second plurality of nanoparticles have a third refractive index that is lower than the first refractive index.   
     
     
         5 . The holographic grating of  claim 1 , wherein the nanoparticles in a given region have a substantially constant concentration with respect to a thickness of the polymer matrix. 
     
     
         6 . The holographic grating of  claim 1 , wherein the polymer matrix comprises a multiplexed volume Bragg grating. 
     
     
         7 . A holographic grating fabricated by a process comprising operations of:
 obtaining a holographic recording material layer;   exposing the holographic recording material layer to a recording light pattern, the recording light pattern creating, in the holographic recording material layer, a first region having a first refractive index and a second region having second refractive index that is higher than the first refractive index; and   after exposing the holographic recording material layer to the recording light pattern, applying a first resin layer comprising a first plurality of nanoparticles to the holographic recording material layer, thereby causing preferential diffusion of at least a portion of the first plurality of nanoparticles into the first region or the second region of the holographic recording material layer, wherein the nanoparticles include monomers.   
     
     
         8 . The holographic grating of  claim 7 , wherein:
 the first plurality of nanoparticles has a third refractive index that is higher than the second refractive index; and   the first plurality of nanoparticles preferentially diffuses into the second region.   
     
     
         9 . The holographic grating of  claim 7 , wherein:
 the first plurality of nanoparticles has a third refractive index that is lower than the second refractive index; and   the first plurality of nanoparticles preferentially diffuses so as to be more highly concentrated in proximity to one or more of a top side or a bottom side of the second region.   
     
     
         10 . The holographic grating of  claim 7 , wherein:
 the first plurality of nanoparticles has a third refractive index lower than the first refractive index; and   the first plurality of nanoparticles preferentially diffuses into the first region.   
     
     
         11 . The holographic grating of  claim 7 , wherein:
 the first plurality of nanoparticles has a third refractive index that is higher than the first refractive index; and   the first plurality of nanoparticles further diffuses so as to be more highly concentrated in proximity to one or more of a top side or a bottom side of the first region.   
     
     
         12 . The holographic grating of  claim 7 , wherein the operations further comprise:
 removing the first resin layer; and   disposing a substrate on the holographic recording material layer.   
     
     
         13 . The holographic grating of  claim 7 , wherein the operations further comprise:
 applying a second resin layer comprising a second plurality of nanoparticles to the holographic recording material layer, thereby causing diffusion of at least a portion of the second plurality of nanoparticles into the holographic recording material layer.   
     
     
         14 . The holographic grating of  claim 7 , wherein the nanoparticles in a given region have a substantially constant concentration with respect to a thickness of the holographic recording material layer. 
     
     
         15 . A holographic grating fabricated by a process comprising operations of:
 obtaining a holographic recording material layer;   applying a first resin layer comprising a first plurality of nanoparticles to the holographic recording material layer; and   after applying the first resin layer, exposing the holographic recording material layer to a recording light pattern, the recording light pattern creating, in the holographic recording material layer, a first region having a first refractive index and a second region having second refractive index that is higher than the first refractive index,   wherein at least a portion of the first plurality of nanoparticles diffuses from the first resin layer into the holographic recording material layer.   
     
     
         16 . The holographic grating of  claim 15 , wherein:
 the first plurality of nanoparticles has a third refractive index that is higher than the second refractive index; and   the first plurality of nanoparticles preferentially diffuses into the second region.   
     
     
         17 . The holographic grating of  claim 15 , wherein:
 the first plurality of nanoparticles has a third refractive index that is lower than the second refractive index; and   the first plurality of nanoparticles diffuse so as to be more highly concentrated in proximity to a top side or a bottom side of the second region.   
     
     
         18 . The holographic grating of  claim 15 , wherein:
 the first plurality of nanoparticles has a third refractive index lower than the first refractive index; and   the first plurality of nanoparticles preferentially diffuses into the first region.   
     
     
         19 . The holographic grating of  claim 15 , wherein:
 the first plurality of nanoparticles has a third refractive index that is higher than the first refractive index; and   the first plurality of nanoparticles diffuse so as to be more highly concentrated in proximity to a top side or a bottom side of the first region.   
     
     
         20 . The holographic grating of  claim 15 , wherein the operations further comprise:
 applying a second resin layer comprising a second plurality of nanoparticles to the holographic recording material layer, thereby causing diffusion of at least a portion of the second plurality of nanoparticles into the holographic recording material layer.