Compound Diffraction Grating and Method of Manufacture
A method including forming a substrate to form a template which includes areas of high relief and areas of low relief; and forming a high refractive index diffraction grating in the template by adding high refractive index material to the template to form a continuous low relief surface The high refractive index material fills the areas of low relief and covers the areas of high relief of the template to form a high refractive index diffraction grating. The high refractive index diffraction grating includes the high refractive index material configured to have a low relief side corresponding to the continuous low relief surface and configured by the template to have a periodic side including areas of high relief and areas of low relief which periodically alternate in the first direction with the first periodicity and are interconnected by the high refractive index material.
1 - 13 . (canceled)
14 . An apparatus comprising:
a high refractive index diffraction grating comprising high refractive index material configured to have a planar side and a periodic side, the periodic side extending in a first direction and comprising areas of high relief and areas of low relief, wherein the areas of high relief and the areas of low relief of the high refractive index material periodically alternate in the first direction with the first periodicity and are interconnected by the high refractive index material to form a plurality of channels, the channels having parallel side walls that are slanted to form an acute angle relative to the first direction; and
wherein the planar side of the high refractive index material contacts a second high refractive index material with a refractive index greater than 1.70, wherein the second high refractive index material defines an exterior surface of the apparatus.
15 . (canceled)
16 . An apparatus as claimed in claim 14 ,
wherein the low relief side of the high refractive index material defines an exterior surface of the apparatus; or
wherein the low relief side of the high refractive index material contacts high refractive index material defining an exterior surface of the apparatus; and/or
wherein the low relief side of the low refractive index material contacts high refractive index material.
17 . An apparatus as claimed in claim 14 comprised in an exit pupil expander .
18 . A method comprising:
forming a substrate in a master mold having a top surface and a plurality of channels in the top surface, the channels having parallel side walls that are slanted to form an acute angle relative to the top surface;
removing the substrate from the master mold to form a template having a periodic side that is continuous and comprises areas of high relief and areas of low relief that periodically alternate in a first direction with a first periodicity; and
forming a high refractive index diffraction grating in the template by adding high refractive index material to the template to form a continuous planar surface , the high refractive index material filling the areas of low relief of the template and covering the areas of high relief of the template to form a high refractive index diffraction grating in the template , wherein the high refractive index diffraction grating comprises the high refractive index material configured to have a planar side corresponding to the continuous planar surface and configured by the template to have a periodic side comprising areas of high relief and areas of low relief, wherein the areas of high relief and the areas of low relief of the high refractive index material periodically alternate in the first direction with the first periodicity and are interconnected by the high refractive index material , wherein the method comprises forming a high refractive index diffraction grating in the template by adding high refractive index material to the template.
19 . A method as claimed in claim 18 , comprising forming a high refractive index diffraction grating in the template by adding high refractive index material to the template using atomic layer deposition.
20 . A method as claimed in claim 18 , comprising forming the high refractive index diffraction grating in the template using titanium dioxide, SrTiO 3 , LiNbO 3 , BaTiO 3 , Y 2 O 3 , MgO, AI 2 O 3 , Si 3 N 4 , SiO 2 , TiN or VN.
21 . A method as claimed in claim 18 , comprising forming a layer of high refractive index material on a side of the template that opposes the periodic side of the template.
22 . A method as claimed in claim 18 , wherein the template comprises polymer.
23 . A method as claimed in claim 18 , comprising forming the template using injection compression molding of the high refractive index material.
24 . A method as claimed in claim 18 , comprising creating a master mold wherein the master mold has a plurality of parallel channels.
25 . A method as claimed in claim 18 , comprising adding a substrate to the planar side of the high refractive index diffraction grating.
26 . A method as claimed in claim 25 , wherein the substrate comprises high refractive index glass.
27 . A method as claimed in claim 18 , wherein the low refractive index template is retained in a direct product of the method or wherein the low refractive index template is not retained and is absent from a direct product of the method exposing the periodic side of the high index diffraction grating to a low refractive index atmosphere.
28 . A method as claimed in claim 18 , comprising forming as a direct product an apparatus as claimed in any of following claim 14 .