Quantitative comparison of gradient index and refractive lenses.

We analyze the Seidel wavefront aberrations and spot sizes of gradient index (GRIN) singlet lenses with Δn≈1. We consider and compare curved and planar GRIN lenses with F-numbers of 5 and 1 against equivalent refractive lenses. We find that the planar GRIN lenses generally have larger spot sizes compared to their refractive lens equivalents at wide angles. This appears to be due to an inability to correct for coma by adjusting the refractive index gradient alone. We can correct for the coma by bending the GRIN lens. This results in a singlet lens with performance close to but not exceeding that of the equivalent refractive lens. We also examine the impact of anisotropy on the planar GRIN lenses. We find that fabricating the planar GRIN lenses from a uniaxial medium has the potential to improve the performance of the lenses.