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 largescale 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.

The epsilon-near-zero (ENZ) multilayer with a vanishing real part of effective permittivity has been proven to have a reflective cutoff effect and an enhanced nonlinear optical response in its ENZ region, making the pulse propagation attract great interest. Here, with the introduction of genetic algorithms (GAs) as a tool to obtain the target spectra, the pulse interactions in A g − S i O 2 alternating stacked multilayers under the ENZ wavelength are numerically studied. It is found that in the original periodic ENZ multilayer, the temporal shapes and spectra first experience a significant attenuation, mainly because of the absorption loss. Afterward, a second peak appears along the propagation path because of localizations and resonances between the layers together with the combined effect of dispersion and nonlinearity. The presented pulse interaction dynamics can provide an insight into the interaction patterns in a periodic ENZ multilayer sample. We use the GAs to obtain a new ENZ multilayer with the same total thicknesses, aperiodic structure, and enhanced reflective properties. The pulse propagation is presented as the physical evidence to further ensure that the optimization has worked well. In this aperiodic sample, the normalized intensity rapidly decreases and the energy is mostly localized near the surface, which indicates the pulse achieves nearly total reflection. Thus, the effect of GA optimization has been confirmed; that is, under extremely high reflection, the pulse can barely propagate through the sample. This optimization toward the reflection spectra of ENZ multilayers could pave the way for a possible design of experimental schemes in a laser cavity, and the cutoff effect of that also could lead to potential applications of pulse shapers and micro/nano Fabry–Perot resonators.

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