Optimization of Epsilon-Near-Zero Multilayers for Near-Perfect Light Absorption Using an Enhanced Genetic Algorithm

Using epsilon-near-zero (ENZ) subwavelength optical multilayer materials with simple structure and thin total thickness to achieve target characteristics is extremely important and beneficial for the realization of on-chip integration and large-scale application of optical devices. Combining with the enhanced genetic algorithm (EGA), this work breaks the limitation of the periodicity of traditional ENZ multilayer structures, and investigates the aperiodic ENZ transparent conducting oxide (TCO)-dielectric multilayer structures. It is realized that under the given conditions, an optimal structure can possess a maximum peak absorption and the broadest absorption bandwidth near the communication wavelength. In the 6-layer structure with a total thickness of 600 nm studied in this work, EGA can optimize the peak absorption from 0.91 to 0.95. Additionally, the absorption bandwidth is optimized from 120 nm to 227 nm, which is enhanced more than 180%. The absorption performance of this optimized structure is comparable to that of a more complex structure with the same total thickness but more layers, or a structure with the same number of layers but a larger total thickness. Conclusively, the proposed EGA optimization method can simplify the structure of the multilayer system, reduce the total thickness of the required ENZ material, and thus greatly simplify the production process and reduce the production cost.