We numerically demonstrate a novel ultra-broadband polarization-independent metamaterial perfect absorber in the visible and near-infrared region involving the phase-change material Ge 2 Sb 2 Te 5 (GST). The novel perfect absorber scheme consists of an array of high-index strong-absorbance GST square resonators separated from a continuous Au substrate by a low-index lossless dielectric layer (silica) and a high-index GST planar cavity. Three absorption peaks with the maximal absorbance up to 99.94% are achieved, owing to the excitation of plasmon-like dipolar or quadrupole resonances from the high-index GST resonators and cavity resonances generated by the GST planar cavity. The intensities and positions of the absorption peaks show strong dependence on structural parameters. A heat transfer model is used to investigate the temporal variation of temperature within the GST region. The results show that the temperature of amorphous GST can reach up to 433 K of the phase transition temperature from room temperature in just 0.37 ns with a relatively low incident light intensity of 1.11 × 10 8 W∕m 2 , due to the enhanced ultra-broadband light absorbance through strong plasmon resonances and cavity resonance in the absorber. The study suggests a feasible means to lower the power requirements for photonic devices based on a thermal phase change via engineering ultra-broadband light absorbers.
We propose an efficient multiband absorber comprised of a truncated, one-dimensional periodic metal-dielectric photonic crystal and a reflective substrate. The reflective substrate is essentially an optically thick metallic film. Such a planar device is easier to fabricate compared to absorbers with complicated shapes. For a four-unit cell device, all four of the absorption peaks can be optimized with efficiencies higher than 95 percent. Moreover, those absorption peaks are insensitive to the polarization and incident angle. The influences of the geometrical parameters and the refractive index of the dielectric on the device performance also are discussed. Furthermore, we found that the number of absorption peaks within each photonic band precisely corresponds to the number of unit cells because the truncated photonic crystal lattices select resonant modes. We also show that the total absorption efficiency gradually increases when there are more periods of the metal-dielectric composite layer placed on top of the metallic substrate. We expect this work to have potential applications in solar energy harvesting and thermal emission tailoring.
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