Wavelength-selective, tunable and switchable plasmonic perfect absorbers based on phase change materials Ge2Sb2Te5

Nanoscale active devices, such as all-optical modulators and electro-optical transducers, can be implemented in heterostructures that integrate plasmonic nanostructures with functional active materials. Here, we demonstrate control over absorption properties in such a heterostructure by coupling the localized surface plasmon resonance (LSPR) of gold nanoantennas to a phase change material (PCM), Ge2Sb2Te5 (GST). The peak absorption of this hybrid absorber approaches near unity at resonance due to the simultaneous excitations of electric and magnetic resonant modes. Moreover, such a hybrid absorber can realize arbitrary wavelength- selective spectral absorption in the mid-infrared region simply by altering the square nanoantennas side length. By controlling the total power of the incident light, the intermediate phases composed of different proportions of the amorphous and crystalline molecules of the GST can be correspondingly tailored, and thus the absorption can be continuously tuned, which provides a flexible and encouraging way to achieve active features once fabricated. Importantly, by converting GST from the amorphous to crystalline state or vice versa, the hybrid absorber can realize bidirectional switching of ON and OFF states, with an outperformed modulation depth of 98% (or 95%) and extinction ratio of -17.15 dB (or -12.98 dB), respectively, indicating its excellent optical modulation performance. Notably, all the stable and intermediate phases of the GST are stable at room temperature, and therefore no sustained external thermal consumption is needed to maintain a desired absorption band for the hybrid scheme. Additionally, the structure can tolerate a wide range of incident angles as well as show polarization-independent features. With these extraordinary optical responses, the proposed scheme could find potential applications in active photonic devices such as optical modulation, thermal imaging and optical switching. Copyright (C) EPLA, 2020