Digital writing of large diffraction grating patterns
A method of fabricating a substrate includes providing a substrate having a flat surface and a beam writing system operable to write in a first direction and a second direction, wherein the second direction is perpendicular to the first direction, The method further includes providing a diffraction grating layout pattern having a first diffraction grating, a second diffraction grating, and a third diffraction grating. The method also includes locating the substrate in the beam writing system, whereby the beam writing system is operable to write into the flat surface, and aligning one of the first, second, and third diffraction gratings parallel with the beam writing system first direction. Additionally, the method includes writing the diffraction grating layout pattern into the substrate flat surface via the beam writing machine.
1. A beam writing system, comprising:
a first platform operable to translate in an x-axis direction and a y-axis direction; and
a second platform operable to rotate about a z-axis perpendicular to said first platform, wherein said second platform is mounted to said first platform;
wherein a substrate may be selectively coupled with said second platform whereby a diffractive feature is always oriented in one of said first platform x-axis and y-axis directions during fabrication,
wherein said beam writing system is configured to write a diffraction pattern layout into a coating of said substrate,
wherein said diffraction pattern layout comprises a first plurality of diffractive features and a second plurality of diffractive features, and
wherein at least one of said first and second pluralities of diffractive features comprise diffractive features having a stepped pattern operable to diffract incident light as if said stepped pattern diffractive features were linear diffractive features.
2. The beam writing system according to claim 1 , wherein said beam writing system is an electron beam lithography system.
3. The beam writing system according to claim 1 , wherein said beam writing system is a laser lithography system.
4. A method of fabricating a substrate, comprising:
providing a substrate having a planar surface comprising a coating;
providing a beam writing system operable to write in a first direction and a second direction, wherein said second direction is perpendicular to said first direction;
providing a diffraction pattern layout, comprising:
a first plurality of linear diffractive features, and
a second plurality of linear diffractive features,
locating said substrate in said beam writing system, wherein said beam writing system is operable to write into said coating;
aligning one of said first and second pluralities of linear diffractive features parallel with said beam writing system first direction; and
writing said diffraction pattern layout into said coating;
wherein at least one of said first and second pluralities of diffractive features comprise diffractive features having a stepped pattern operable to diffract incident light as if said stepped pattern diffractive features were linear diffractive features.
5. The method of fabricating a substrate according to claim 4 , wherein one of said first and second pluralities of diffractive features is not aligned parallel with either of said beam writing system first and second directions.
6. The method of fabricating a substrate according to claim 4 , wherein said second plurality of linear diffractive features comprises a greater total area than said first plurality of linear diffractive features, and wherein said diffraction pattern layout is oriented such that said second plurality of linear diffractive features is aligned parallel with said beam writing system first direction.
7. The method of fabricating a substrate according to claim 6 , wherein said second plurality of linear diffractive features comprises a diffractive feature duty cycle less than 50%.
8. The method of fabricating a substrate according to claim 4 , wherein a duty cycle of said diffractive features of at least one of said first and second plurality of linear diffractive features is less than 50%.
9. The method of fabricating a substrate according to claim 4 , wherein said plurality of diffractive features aligned parallel with said beam writing system first direction are oriented within 1 arc minute of parallel with said beam writing system first direction.
10. The method of fabricating a substrate according to claim 4 , wherein said plurality of diffractive features aligned parallel with said beam writing system first direction are oriented within 1 arc second of parallel with said beam writing system first direction.
11. The method of fabricating a substrate according to claim 4 , wherein said diffraction pattern layout further comprises a third plurality of linear diffractive features,
said first plurality of linear diffractive features forming an in-coupling diffraction grating,
said second plurality of linear diffractive features forming a turning diffractive optic arranged optically between said first plurality of linear diffractive features and said third plurality of linear diffractive features,
said third plurality of linear diffractive features forming an out-coupling diffractive optic,
wherein said second plurality of linear diffractive features is aligned parallel with said beam writing system first direction.
12. The method of fabricating a substrate according to claim 11 , wherein:
said first and third pluralities of linear diffractive features are not aligned parallel with one of said beam writing system first and second directions;
said first and third pluralities of linear diffractive features comprise diffractive features having a stepped pattern forming substantially linear diffractive features; and
said first and third pluralities of linear diffractive features are disposed in bilateral symmetric orientation about said second plurality of linear diffractive features.
13. The method of fabricating a substrate according to claim 12 , wherein said first and third pluralities of linear diffractive features are written into said coating as stepped line diffractive features, the method further comprising molding a waveguide operable to propagate image-bearing light via total internal reflection, wherein an angular error induced in image-bearing light diffracted by said stepped line diffractive features is corrected via said bilateral symmetric orientation.
14. The method of fabricating a substrate according to claim 11 , wherein said first plurality of linear diffractive features defines a first grating vector, said second plurality of linear diffractive features defines a second grating vector, and said third plurality of linear diffractive features defines a third grating vector, wherein a vector sum of said first, second, and third grating vectors is approximately zero.
15. The method of fabricating a substrate according to claim 4 , further comprising molding a waveguide utilizing said substrate.
16. The method of fabricating a substrate according to claim 4 , wherein said substrate is a waveguide for a virtual image near-eye display system.
17. The method of fabricating a substrate according to claim 4 , wherein said stepped pattern comprises a first write path direction and a second write path direction, consecutive portions of said first write path direction and said second write path direction forming said stepped pattern.
18. The method of fabricating a substrate according to claim 4 , wherein said diffraction pattern layout further comprises a third plurality of linear diffractive features, and wherein said first, second, and third plurality of linear diffractive features form contiguous chordal segments of a curve.