Material optimization in the design of broadband gradient-index optics

Gradient-index (GRIN) optics are commonly optimized with pre-determined materials, but the material choices limit the solution space of optimized index profiles. If the dispersive properties of the materials generating GRIN can be optimized, the performance of the optics can be further improved. This paper proposes a material concentration-based GRIN representation to replace the widely-used index-based representation, allowing simultaneous optimization of materials and the GRIN profile. The paper also proposed an efficient iterative algorithm capable of calculating the refractive indices, Abbe numbers and partial dispersions of material pairs from the optimized GRIN profiles. The new representation and the algorithm are used to optimize an F/2.5 GRIN singlet to diffraction-limited performance over the visible spectrum.