Evacuated Periotic Structures and Methods of Manufacturing

Abstract

Improvements to gratings for use in waveguides and methods of producing them are described herein. Deep surface relief gratings (SRGs) may offer many advantages over conventional SRGs, an important one being a higher S-diffraction efficiency. In one embodiment, deep SRGs can be implemented as polymer surface relief gratings or evacuated periodic structures (EPSs). EPSs can be formed by first recording a holographic polymer dispersed liquid crystal (HPDLC) periodic structure. Removing the liquid crystal from the cured periodic structure provides a polymer surface relief grating. Polymer surface relief gratings have many applications including for use in waveguide-based displays.

What is claimed is: 
     
         1 . A waveguide device comprising:
 a waveguide supporting a polymer grating structure for diffracting light propagating in total internal reflection in said waveguide, wherein the polymer grating structure comprises:
 a polymer regions; 
 air gaps between adjacent portions of the polymer regions; 
 an optical layer disposed between the polymer regions and the waveguide; and 
 a coating disposed on the tops of the polymer regions and the tops of the optical layer. 
   
     
     
         2 . The waveguide device of  claim 1 , wherein the coating comprises an atomic layer deposition (ALD) deposited metallic layer or dielectric layer to enhance evanescent coupling between the waveguide and the polymer grating structure. 
     
     
         3 . The waveguide device of  claim 1 , wherein the coating comprises an atomic layer deposition (ALD) deposited metallic layer or dielectric layer to enhance the effective refractive index of the polymer grating structure. 
     
     
         4 . The waveguide device of  claim 1 , wherein the coating comprises an atomic layer deposition (ALD) deposited metallic layer or dielectric layer to enhance adhesion and/or perform as a bias layer. 
     
     
         5 . The waveguide device of  claim 1 , wherein the coating comprises an atomic layer deposition (ALD) conformally deposited metallic layer or dielectric layer disposed over the entirety of the polymer regions and the exposed tops of the optical layer. 
     
     
         6 . The waveguide device of  claim 1 , wherein the coating comprises an atomic layer deposition (ALD) deposited metallic layer or dielectric layer disposed over one or more facets of the polymer regions including one or more of the upper, lower, or sidewall facets of the polymer regions. 
     
     
         7 . The waveguide device of  claim 1 , wherein a passivation coating is applied to the surfaces of the polymer grating structure. 
     
     
         8 . The waveguide device of  claim 1 , wherein the polymer regions include a slant angle with respect to the waveguide. 
     
     
         9 . The waveguide device of  claim 1 , wherein the polymer grating structure further comprises an isotropic material between adjacent portions of the polymer network, wherein the isotropic material has a refractive index higher or lower than the refractive index of the polymer network. 
     
     
         10 . The waveguide device of  claim 9 , wherein the isotropic material occupies a space at a bottom portion of the space between adjacent portions of the polymer network and the air occupies the space from above the top surface of the isotropic material to the modulation depth. 
     
     
         11 . The waveguide device of  claim 9 , wherein the isotropic material comprises a birefringent crystal material. 
     
     
         12 . The waveguide device of  claim 11 , wherein the birefringent crystal material comprises a liquid crystal material. 
     
     
         13 . The waveguide device of  claim 11 , wherein the refractive index difference between the polymer network and the birefringent crystal material is 0.05 to 0.2. 
     
     
         14 . The waveguide device of  claim 1 , wherein the polymer grating structure has a modulation depth greater than a wavelength of visible light. 
     
     
         15 . The waveguide device of  claim 1 , wherein the polymer grating structure comprises a modulation depth and a grating pitch and wherein the modulation depth is greater than the grating pitch. 
     
     
         16 . The waveguide device of  claim 1 , wherein the waveguide comprises two substrates and the polymer grating structure is either sandwiched between the two substrates or positioned on an external surface of either substrate. 
     
     
         17 . The waveguide device of  claim 1 , wherein the Bragg fringe spacing of the polymer network is 0.35 μm to 0.8 μm and the grating depth of the polymer network is 1 μm to 3 μm. 
     
     
         18 . The waveguide device of  claim 1 , wherein the ratio of grating depth of the polymer network to the Bragg fringe spacing is 1:1 to 5:1. 
     
     
         19 . The waveguide device of  claim 1 , further comprising a picture generating unit, and wherein the polymer grating structure comprises a waveguide diffraction grating. 
     
     
         20 . The waveguide device of  claim 19 , wherein the waveguide diffraction grating is configured as a multiplexing grating. 
     
     
         21 . The waveguide device of  claim 20 , wherein the waveguide diffraction grating is configured to accept light from the picture generating unit which includes multiple images. 
     
     
         22 . The waveguide device of  claim 21 , wherein the waveguide diffraction grating is configured to outcouple light from the waveguide. 
     
     
         23 . The waveguide device of  claim 19 , wherein the waveguide diffraction grating is configured as a beam expander. 
     
     
         24 . The waveguide device of  claim 19 , wherein the waveguide diffraction grating is configured to incouple light including image data generated from the picture generating unit. 
     
     
         25 . The waveguide device of  claim 24 , wherein the waveguide diffraction grating is further configured to incouple S-polarized light with a high degree of efficiency. 
     
     
         26 . The waveguide device of  claim 25 , wherein the diffraction grating is further configured to incouple S-polarized light at an efficiency of 70% to 95% at a Bragg angle. 
     
     
         27 . The waveguide device of  claim 25 , wherein the diffraction grating is further configured to incouple P-polarized light at an efficiency of 25% to 50% at a Bragg angle. 
     
     
         28 . The waveguide device of  claim 1 , wherein the refractive index difference between the polymer network and the air gaps is 0.25 to 0.4. 
     
     
         29 . The waveguide device of  claim 1 , wherein the polymer grating structure comprises a two-dimensional lattice structure or a three-dimensional lattice structure. 
     
     
         30 . The waveguide device of  claim 1 , further comprising another grating structure, wherein the polymer grating structure comprises an incoupling grating and the other grating structure comprises a beam expander or an outcoupling grating.