Optical devices based on diffraction gratings
Embodiments of the present invention relate to planar optical devices composed of one or more sub-wavelength diffraction grating layers. In one embodiment, an optical device includes a first substantially planar reflective structure ( 104,1904 ), a second substantially planar reflective structure ( 106,1906 ), and a substantially planar sub-wavelength grating layer ( 102,1902 ) disposed between the first reflective structure and the second reflective structure. The grating layer is configured with lines ( 208 - 211,214 - 217 ) having line widths, line thicknesses, and line period spacing selected to control phase changes in different portions of a beam of light transmitted through the optical device.
1. An optical device comprising:
a first substantially planar reflective structure;
a second substantially planar reflective structure;
a substantially planar sub-wavelength diffraction grating layer disposed between the first reflective structure and the second reflective structure, wherein at least one of the first reflective structure and the second reflective structure are configured as sub-wavelength diffraction grating layers, wherein the substantially planar sub-wavelength diffraction grating layer is configured with lines having line widths, line thicknesses, and line period spacing selected to control phase changes in different portions of a beam of light transmitted through the optical device;
a first resonant cavity formed between the first reflective structure and the substantially planar sub-wavelength diffraction grating layer; and
a second resonant cavity formed between the second reflective structure and the substantially planar sub-wavelength diffraction grating layer.
2. The optical device of claim 1 , wherein one of the first reflective structure and the second reflective structure is a reflective plate.
3. The optical device of claim 1 , wherein
the first resonant cavity and the second resonant cavity are air filled; or
the first resonant cavity and the second resonant cavity are filled with a material having lower refractive index than the refractive indices associated with the first reflective structure, the second reflective structure and the substantially planar sub-wavelength diffraction grating layer.
4. The optical device of claim 1 , wherein the substantially planar sub-wavelength diffraction grating layer further comprising a substrate, with a grating pattern disposed on a surface of the substrate and the grating pattern is formed in a material having a higher refractive index than the substrate.
5. The optical device of claim 1 , wherein the substantially planar sub-wavelength diffraction grating layer further comprises a membrane.
6. The optical device of claim 4 , wherein the grating pattern further comprises a one-dimensional pattern of lines.
7. The optical device of claim 6 , wherein the one-dimensional pattern of lines further comprises one or more sub-regions of lines, the lines within each sub-region having a selected period and line width.
8. The optical device of claim 1 , wherein the lines width, line thickness, and line period spacing are selected to form a convex lens.
9. The optical device of claim 1 , wherein the lines widths, line thickness, and line period spacing are selected to form a concave lens.
10. The optical device of claim 1 , wherein the line width, line thickness, and line period spacing are selected to form a prism.
11. A method for fabricating a sub-wavelength grating layer of an optical device using a computing device, the method comprising:
calculating a desired target phase change across the optical device using the computing device, the target phase change corresponding to a desired wavefront shape in a beam of light transmitted through the optical device;
generating line widths, line period spacing, and line thickness corresponding to the target phase change across the sub-wavelength grating layer using the computing device; and
generating a set of coordinates using the computing device, each coordinate identifying the location of a line with a line width, line period spacing, and line thickness.
12. The method of claim 11 further comprising:
depositing a first layer of material corresponding to a planar first reflective structure;
depositing a first polymer material layer over the first layer;
depositing a second layer of material over the first polymer layer;
defining a grating pattern of lines in the second layer corresponding to a sub-wavelength gating pattern based on the set of coordinates;
depositing a second polymer material layer over the second layer and
depositing a third layer of material corresponding to a planar second reflective structure.
13. The method of claim 12 further comprising defining a grating pattern of lines in the first layer corresponding to the first reflective structure and/or the second layer corresponding to the second reflective structure.
14. The method of claim 11 further comprising:
arranging a first layer of material corresponding to a first planar reflective structure;
forming a grating pattern of lines in a second layer corresponding to a sub-wavelength gating pattern based on the set of coordinates;
arranging the second layer of material a given distance over the first layer; and
arranging a third layer of material corresponding to a second planar reflective structure over the second layer.
15. The method of claim 14 , wherein a space between the first layer and the second layer is a first resonant cavity and a space between the second layer and the third layer is a second resonant cavity, the first resonant cavity and the second resonant cavity being air filled.
16. The method of claim 11 , wherein the line widths, line period spacing, and line thickness are selected to form a convex lens.
17. The method of claim 11 , wherein the line widths, line period spacing, and line thickness are selected to form a concave lens.
18. The method of claim 11 , wherein the line widths, line period spacing, and line thickness are selected to form a prism.