Lens with concentric hemispherical refractive structures

1. A lens comprising:

a first hemispherical refractive structure having a first effective refractive index based on a first fill pattern of the first hemispherical refractive structure; and

a second hemispherical refractive structure having a second effective refractive index based on a second fill pattern of the second hemispherical refractive structure, the second hemispherical refractive structure arranged as a hemispherical shell coupled to and concentric with the first hemispherical refractive structure, wherein the second effective refractive index is different than the first effective refractive index.

2. The lens of claim 1 , wherein the first hemispherical refractive structure includes a first plurality of plate structures, and wherein the second hemispherical refractive structure includes a second plurality of plate structures.

3. The lens of claim 2 , wherein the first effective refractive index is based on a first number of plate structures of the first plurality of plate structures, and wherein the second effective refractive index is based on a second number of plate structures of the second plurality of plate structures, the second number different than the first number.

4. The lens of claim 2 , wherein the first effective refractive index is based on a first spacing between plate structures of the first plurality of plate structures, and wherein the second effective refractive index is based on a second spacing between plate structures of the second plurality of plate structures, the second spacing different than the first spacing.

5. The lens of claim 1 , wherein the first fill pattern includes one of a linear fill pattern, a triangular fill pattern, a diagonal fill pattern, or a hexagonal fill pattern, and wherein the second fill pattern includes another of the linear fill pattern, the triangular fill pattern, the diagonal fill pattern, or the hexagonal fill pattern.

6. The lens of claim 1 , wherein the first hemispherical refractive structure has a first fill density, and wherein the second hemispherical refractive structure has a second fill density different than the first fill density.

7. The lens of claim 1 , wherein the first effective refractive index and the second effective refractive index define a gradient refractive index of a Luneburg lens.

8. The lens of claim 1 , wherein the first effective refractive index and the second effective refractive index define a gradient refractive index of a fisheye lens.

9. A method of fabricating a lens, the method comprising:

forming a first hemispherical refractive structure of a lens, the first hemispherical refractive structure having a first effective refractive index based on a first fill pattern of the first hemispherical refractive structure; and

forming a second hemispherical refractive structure of the lens as a hemispherical shell that is coupled to and concentric with the first hemispherical refractive structure, the second hemispherical refractive structure having a second effective refractive index based on a second fill pattern of the second hemispherical refractive structure, wherein the second effective refractive index is different than the first effective refractive index.

10. The method of claim 9 , wherein the first hemispherical refractive structure and the second hemispherical refractive structure are formed using an additive manufacturing process.

11. The method of claim 9 , wherein forming the first hemispherical refractive structure includes forming a first plurality of plate structures dimensioned to provide the first effective refractive index, and wherein forming the second hemispherical refractive structure includes forming on the first hemispherical refractive structure a second plurality of plate structures dimensioned to provide the second effective refractive index.

12. The method of claim 9 , wherein forming the first hemispherical refractive structure includes forming a first plurality of plate structures having a first spacing to provide the first effective refractive index, and wherein forming the second hemispherical refractive structure includes forming on the first hemispherical refractive structure a second plurality of plate structures having a second spacing to provide the second effective refractive index.

13. The method of claim 9 , wherein forming the first hemispherical refractive structure includes forming a first plurality of plate structures having the first fill pattern to provide the first effective refractive index, and wherein forming the second hemispherical refractive structure includes forming on the first hemispherical refractive structure a second plurality of plate structures having the second fill pattern to provide the second effective refractive index.

14. The method of claim 9 , wherein the first fill pattern includes one of a linear fill pattern, a triangular fill pattern, a diagonal fill pattern, or a hexagonal fill pattern, and wherein the second fill pattern includes another of the linear fill pattern, the triangular fill pattern, the diagonal fill pattern, or the hexagonal fill pattern.

15. The method of claim 9 , wherein forming the first hemispherical refractive structure includes forming a first plurality of plate structures having a first fill density to provide the first effective refractive index, and wherein forming the second hemispherical refractive structure includes forming on the first hemispherical refractive structure a second plurality of plate structures having a second fill density to provide the second effective refractive index.

16. A method of focusing a signal using a lens, the method comprising:

receiving a first signal at a lens; and

focusing the first signal to generate a second signal using a first hemispherical refractive structure of the lens and using a second hemispherical refractive structure of the lens, the first hemispherical refractive structure having a first effective refractive index based on a first fill pattern of the first hemispherical refractive structure, the second hemispherical refractive structure arranged as a hemispherical shell coupled to and concentric with the first hemispherical refractive structure, the second hemispherical refractive structure having a second effective refractive index based on a second fill pattern of the second hemispherical refractive structure, wherein the second effective refractive index is different than the first effective refractive index.

17. The method of claim 16 , wherein the lens corresponds to a Luneburg lens.

18. The method of claim 16 , wherein the lens corresponds to a fisheye lens.

19. The method of claim 16 , further comprising outputting the second signal to a waveguide.

20. The method of claim 16 , further comprising outputting the second signal to a radio antenna.