Synthesizing low loss negative index metamaterial stacks for the mid-infrared using genetic algorithms

Negative index metamaterial designs for the mid-infrared with low absorption and impedance mismatch losses are presented. A robust genetic algorithm is employed to optimize the flexible metamaterial structure for targeted refractive index and impedance values. A new figure of merit is introduced to evaluate the impedance match of the metamaterial to free space. Two designs are presented demonstrating low-loss characteristics for a thin metamaterial with two metal screens and a thick metamaterial stack with five screens. The device performance is analyzed when adding more screens to the structure, revealing that optimizing a thick stack produces a metamaterial with properties approaching those of a bulk material.