Pulse interactions in periodic and genetic-algorithm-optimized aperiodic epsilon-near-zero multilayers

Abstract

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.