A lens includes a first hemispherical refractive structure having a first effective refractive index based on a first fill pattern of the first hemispherical refractive structure. The lens further includes 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 is arranged as a hemispherical shell coupled to and concentric with the first hemispherical refractive structure. The second effective refractive index is different than the first effective refractive index.