Diffractive optical element fabrication
Described herein are embodiments of a diffractive optical element ( 23 ) such as a grism. In one embodiment, the diffractive optical element ( 23 ) includes an input surface ( 31 ) configured to receive an input optical signal ( 29 ), a diffractive surface ( 33 ) adapted to spatially disperse the input optical beam ( 29 ) into a dispersed signal and an output surface ( 35 ) configured to output the dispersed signal from the diffractive optical element. The input surface ( 31 ) and the diffractive surface ( 33 ) are non-parallel and the diffractive surface ( 33 ) is formed in situ by a photolithographic technique.
1. A method of fabricating a diffractive optical element, the method including the steps:
depositing a pattern material layer of pattern material directly onto a first surface of a non-cuboid prism, wherein the first surface is non parallel to either or both of an input surface configured to receive an input optical signal and an output surface configured to output a dispersed signal from the diffractive optical element;
applying a photoresist layer to the pattern material layer;
creating a diffractive pattern in the photoresist layer by illuminating the photoresist layer through a photo mask while moving the photoresist layer substantially perpendicular relative to the photo mask; and
transferring the diffractive pattern in the photoresist layer to the pattern material layer to define a diffractive surface on the first surface.
2. The method of fabricating the diffractive optical element according to claim 1 wherein:
the diffractive surface and the output surface are non-parallel;
the input surface and the diffractive surface are non-parallel;
the input surface is the output surface;
the input surface is the diffractive surface; or
the input surface and the diffractive surface are separated by a distance of greater than 5 mm.
3. The method of fabricating the diffractive optical element according to claim 1 wherein the diffractive optical element is a triangular prism, a trapezoid, or a non-wafer structure.
4. The method of fabricating the diffractive optical element according to claim 1 wherein creating the diffractive pattern in the photoresist layer comprises using a light source.
5. The method of fabricating the diffractive optical element according to claim 1 wherein the pattern material is selected from one or more of Si3N4, TiO2, HfO2, amorphous silicon, high refractive index polymer, spin-on-glass, photoresist, reflective metal, chromium, gold, silver, aluminum, nickel, and Ta205.
6. The method of fabricating the diffractive optical element according to claim 1 wherein the photoresist layer includes an anti-reflective coating and primer.
7. The method of fabricating the diffractive optical element according to claim 1 wherein the movement is substantially continuous or stepwise.
8. The method of fabricating the diffractive optical element according to claim 1 wherein the photoresist layer is moved a distance of
z
T
=
2
p
2
λ
where p is a spatial period of the photo mask and λ is a wavelength of the illumination.
9. The method of fabricating the diffractive optical element according to claim 7 wherein the photoresist layer is moved a distance of
z
T
=
2
p
2
λ
where p is a spatial period of the photo mask and λ is a wavelength of the illumination.
10. The method of fabricating the diffractive optical element according to claim 1 wherein the diffractive optical element is configured to operate in a wavelength selective switch; and/or wherein the input optical signal includes a plurality of optical wavelength channels.
11. The method of fabricating the diffractive optical element according to claim 1 wherein the diffractive optical element includes a lens.
12. A method of fabricating a diffractive optical element, the method including the steps:
depositing a photoresist layer directly onto a first surface of a non-cuboid prism, wherein the first surface is non parallel to either or both of an input surface configured to receive an input optical signal and an output surface configured to output a dispersed signal from the diffractive optical element; and
creating a diffractive pattern in the photoresist layer to define a diffraction surface on the first surface by illuminating the photoresist layer through a photo mask while moving the photoresist layer substantially perpendicular relative to the photo mask.
13. The method of fabricating the diffractive optical element according to claim 12 wherein creating the diffractive pattern in the photoresist layer comprises using a light source.
14. The method of fabricating the diffractive optical element according to claim 12 wherein:
the diffractive surface and the output surface are non-parallel;
the input surface and the diffractive surface are non-parallel;
the input surface is the output surface;
the input surface is the diffractive surface;
the input surface and the diffractive surface are separated by a distance of greater than 5 mm; or
the diffractive optical element is configured to operate in a wavelength selective switch.
15. The method of fabricating the diffractive optical element according to claim 12 wherein the diffractive optical element includes a lens.
16. The method of fabricating the diffractive optical element according to claim 12 wherein the pattern material is selected from one or more of Si3N4, TiO2, HfO2, amorphous silicon, high refractive index polymer, spin-on-glass, photoresist, reflective metal, chromium, gold, silver, aluminum, nickel, and Ta2O5.
17. The method of fabricating the diffractive optical element according to claim 12 wherein the photoresist layer includes an anti-reflective coating and primer.
18. The method of fabricating the diffractive optical element according to claim 12 wherein the movement is substantially continuous or stepwise.
19. The method of fabricating the diffractive optical element according to claim 12 wherein the photoresist layer is moved a distance of
z
T
=
2
p
2
λ
where p is a spatial period of the photo mask and λ is a wavelength of the illumination.
20. The method of fabricating the diffractive optical element according to claim 12 wherein creating the diffractive pattern by illuminating the photoresist layer through the photo mask while moving the photoresist layer substantially perpendicular relative to the photo mask comprises producing an irradiance field having a first spatial period that is half of a second spatial period of the photo mask.
21. The method of fabricating the diffractive optical element according to claim 12 wherein creating the diffractive pattern by illuminating the photoresist layer through the photo mask while moving the photoresist layer substantially perpendicular relative to the mask comprises one or more of:
relaxing tilt alignment between the photo mask and the first surface of the non-cuboid prism;
relaxing flatness of the first surface of the non-cuboid prism; and
relaxing ultraviolet light for the illumination to a longer wavelength.
22. The method of fabricating the diffractive optical element according to claim 12 comprising using the photo mask that is multiple times larger than the first surface of the non-cuboid prism; aligning multiple ones of the non-cuboid prism to the same photo mask; and simultaneously exposing the multiple non-cuboid prisms with the illumination.
23. The method of fabricating the diffractive optical element according to claim 1 wherein creating the diffractive pattern by illuminating the photoresist layer through the photo mask while moving the photoresist layer substantially perpendicular relative to the photo mask comprises producing an irradiance field having a first spatial period that is half of a second spatial period of the photo mask.
24. The method of fabricating the diffractive optical element according to claim 1 wherein creating the diffractive pattern by illuminating the photoresist layer through the photo mask while moving the photoresist layer substantially perpendicular relative to the photo mask comprises one or more of:
relaxing tilt alignment between the photo mask and the first surface of the non-cuboid prism;
relaxing flatness of the first surface of the non-cuboid prism; and
relaxing ultraviolet light for the illumination to a longer wavelength.
25. The method of fabricating the diffractive optical element according to claim 1 comprising using the photo mask that is multiple times larger than the first surface of the non-cuboid prism; aligning multiple ones of the non-cuboid prism to the same photo mask; and simultaneously exposing the multiple non-cuboid prisms with the illumination.