Planar, high NA, low loss transmitting or reflecting lenses using sub-wavelength high contrast grating
Planar lenses and reflectors are described comprising subwavelength high-contrast gratings (HCG) having high index of refraction grating elements spaced apart from one another in straight and/or curved segments and surrounded by low index material. The high-contrast grating is configured to receive an incident wave which excites multiple modes within the high-contrast grating and is focused for reflection and/or transmission by said high contrast grating. The width of the high contrast grating bars vary along a distribution direction of the grating bars which is perpendicular to the length of the grating bars and/or varies along the length of one or more grating bars to focus said reflection and/or transmission. The HCG is configured to provide double focusing, whose use is exemplified within a vertical cavity surface emitting laser (VCSEL) structure using focusing HCG structures for both the top and bottom mirrors.
1. An apparatus for focusing optical energy, comprising:
a high-contrast grating (HCG) having grating elements spaced apart from one another;
said grating elements having subwavelength width and spacing and an index of refraction at or exceeding approximately 2;
a material, or materials, with a low refractive index surrounding said grating elements;
wherein said high-contrast grating is configured to focus for reflection and/or transmission; and
wherein grating element width and spacing varies to focus said reflection and/or transmission to a desired location in relation to said high-contrast grating;
wherein said high-contrast grating is configured to provide double focusing with both reflected and transmitted waves being focused.
2. The apparatus recited in claim 1 , wherein said high-contrast grating is planar.
3. The apparatus recited in claim 1 , wherein said high-contrast grating is configured for high reflectivity, partial reflectivity, or high transmissivity.
4. The apparatus recited in claim 1 , wherein said high-contrast grating is configured to allow selection of a wide range of phases while maintaining a certain reflectivity magnitude.
5. The apparatus recited in claim 1 , wherein said high contrast grating comprises parallel bars of material having a high index of refraction and surrounded by a material having a low index of refraction.
6. The apparatus recited in claim 1 , wherein said high contrast grating comprises curving bars of material having a high index of refraction and surrounded by a material, or materials, having a low index of refraction.
7. The apparatus recited in claim 6 , wherein said high contrast grating comprises concentric circular bars of material having a high index of refraction and surrounded by a material, or materials, having a low index of refraction.
8. The apparatus recited in claim 1 , wherein said high contrast grating has grating elements whose spacing is varied along a distribution direction of said high-contrast grating elements to provide varying phase changes along a length of said high-contrast grating to focus said reflection and/or transmission.
9. The apparatus recited in claim 1 , wherein the width of the high contrast grating bars vary along a distribution direction of the grating bars which is perpendicular to the length of the grating bars to focus said reflection and/or transmission.
10. The apparatus recited in claim 1 , wherein both width and spacing of the high contrast grating bars vary along a distribution direction of the grating bars which is perpendicular to the length of the grating bars to focus said reflection and/or transmission.
11. The apparatus recited in claim 1 , wherein the width of the high contrast grating bars varies along the length of one or more grating bars to focus said reflection and/or transmission.
12. The apparatus recited in claim 1 , wherein three physical parameters control reflectivity of the grating, comprising spacing, thickness, and width of the grating elements.
13. The apparatus recited in claim 1 , wherein said optical energy is focused from a normally incident wave.
14. The apparatus recited in claim 1 , wherein said high-contrast grating is configured for receiving said optical energy in a Transverse-Magnetic (TM) polarization.
15. The apparatus recited in claim 1 , wherein said high-contrast grating is configured for receiving said optical energy in a Transverse-Electric (TE) polarization.
16. The apparatus recited in claim 1 , wherein width and position of each grating element of said high contrast grating are selected in response to selecting a straight or curved line path along a phase contour map which only traverses regions of desired reflectivity.
17. The apparatus recited in claim 16 , wherein said width and position of each grating element of said high contrast grating is further determined in response to a bar-by-bar optimization process in which the dimensions of each grating element (bar) is adjusted to minimize energy leakage to a transmission side for a reflector or a reflection side for a lens.
18. An apparatus for focusing optical energy, comprising:
a high-contrast grating (HCG) having grating elements spaced apart from one another;
said grating elements having subwavelength dimensions and an index of refraction at or exceeding approximately 2; and
a low index of refraction material, or materials, surrounding said grating elements;
wherein said HCG is configured to receive an incident wave that is focused for reflection and/or transmission by said HCG;
said grating elements having width and spacing that varies to focus said reflection and/or transmission to a desired location in relation to said grating;
wherein said HCG is chirped in response to varying grating element spacing and/or width along a distribution direction of said grating elements to provide varying phase changes along a length of said HCG to focus said reflection and/or transmission; and
wherein said HCG is configured to provide double focusing with both the reflected and transmitted waves being focused.
19. The apparatus recited in claim 18 , wherein the width and/or spacing of the grating elements is configured to vary along a distribution direction of the grating elements which is perpendicular to the length of the grating elements and varies along the length of one or more grating elements to focus said reflection and/or transmission in two dimensions.