High index contrast grating structure for light manipulation and related method
View Patent ↗A high index contrast grating (HICG) structure is disclosed. The HICG structure includes plurality of gratings fabricated from a high refractive index layer. The high refractive index layer is situated over a low refractive index substrate, wherein the high refractive index layer is patterned after determining a period and a duty cycle of each of the plurality of gratings for a desired reflection phase profile based on a lookup table. The low refractive index substrate includes sapphire. The plurality of gratings includes polycrystalline or amorphous silicon. The HICG structure includes subwavelength gratings for incident wavelengths of equal to or greater than 2.5 microns. An exemplary method for forming the HICG structure is also disclosed.
1. A high index contrast grating (HICG) structure comprising:
a plurality of gratings fabricated from a high refractive index layer, said plurality of gratings including a first grating, a second grating adjacent said first grating, and a third grating adjacent said second grating such that said second grating is situated between said third grating and said first grating;
wherein said high refractive index layer is situated over a low refractive index substrate;
and wherein said high refractive index layer is patterned after determining a combination of a period, a thickness, and a duty cycle of each of said plurality of gratings for a desired reflection phase profile;
said combination being determined for said first grating based on a lookup table;
said combination being determined for said second grating using a location and a period of said first grating and based on said lookup table; and
said combination being determined for said third grating using a location and a period of said second grating and based on said lookup table.
2. The HICG structure of claim 1 , wherein said low refractive index substrate includes silicon nitride.
3. The HICG structure of claim 1 , wherein at least one of said plurality of gratings includes amorphous silicon.
4. The HICG structure of claim 1 , wherein at least one of said plurality of gratings includes polycrystalline silicon.
5. The HICG structure of claim 1 , wherein said high refractive index layer has a refractive index at least two times greater than that of said low refractive index substrate.
6. The HICG structure of claim 1 , wherein said HICG structure includes subwavelength gratings for incident wavelengths of equal to or greater than 2.5 microns.
7. The HICG structure of claim 1 , wherein said HICG structure functions as a combinatory optical system having multiple components on said low refractive index substrate.
8. The HICG structure of claim 1 , wherein said HICG structure is a mid-infrared reflective mirror having a reflectivity of approximately 100%.
9. The HICG structure of claim 1 , wherein said HICG structure has a reflection phase profile of a blazed grating.
10. The HICG structure of claim 1 , wherein said HICG structure has a reflection phase profile of a focusing reflector.
11. A method of forming a high index contrast grating (HICG) structure, said method comprising:
providing a lookup table containing transmissivity and/or reflectivity data corresponding to pre-determined wavelengths;
forming a high refractive index layer over a low refractive index substrate;
determining a combination of a period, a thickness, and a duty cycle of each of a plurality of gratings for a desired transmission or reflection profile, said plurality of gratings including a first grating, a second grating adjacent said first grating, and a third grating adjacent said second grating such that said second grating is situated between said third grating and said first grating;
wherein determining said combination for said first grating is performed based on said lookup table;
wherein determining said combination for said second grating is performed using a location and a period of said first grating and based on said lookup table;
wherein determining said combination for said third grating is performed using a location and a period of said second grating and based on said lookup table; and
patterning said high refractive index layer to form said plurality of gratings.
12. The method of claim 11 , wherein said transmissivity and/or reflectivity data includes transmissivity and/or reflectivity phase data.
13. The method of claim 11 , wherein said transmissivity and/or reflectivity data includes transmissivity and/or reflectivity amplitude data.
14. The method of claim 11 , wherein said HICG structure is configured to transmit a wave through said HICG structure, such that said HICG structure functions as a focusing lens, a divergence lens, or a high numerical aperture lens.
15. The method of claim 11 , wherein said HICG structure is configured to transmit a wave through said HICG structure, such that said transmitted wave has amplitude and phase profiles of a diffraction grating.
16. The method of claim 11 , wherein said HICG structure is configured to reflect a wave, such that said HICG structure functions as a concave mirror, a convex mirror, a focusing lens, or a divergence lens.
17. The method of claim 11 , wherein said HICG structure is configured to reflect a wave, such that said reflected wave has amplitude and phase profiles of a diffraction grating.
18. The method of claim 11 , wherein said HICG structure is a mid-infrared reflective mirror having a reflectivity of approximately 100%.
19. The method of claim 11 , wherein said HICG structure is configured to reflect a wave, such that said reflected wave has amplitude and phase profiles of a blazed grating.
20. The method of claim 11 , wherein said HICG structure includes subwavelength gratings for incident wavelengths of equal to or greater than 2.5 microns.