Combining Switchable Phase-Change Materials and Phase-Transition Materials for Thermally Regulated Smart Mid-Infrared Modulators

Phase-change materials (PCMs) and phase-transition materials (PTMs) both show a large contrast in their respective optical properties upon switching, enabling compact optical components with diverse functionalities like sensing, thermal imaging, and data recording. However, their switching properties differ significantly, that is, the switching is non-volatile for PCMs while volatile for PTMs. Here, new-generation smart mid-infrared modulators with switchable transmission, reflection, and absorption are demonstrated conceptually and experimentally, which combine one PCM (Ge3Sb2Te6 or In3SbTe2) with one PTM (VO2) as two active layers. The bottom VO2 layer is employed as a thermally regulated (modulated) dynamic mirror, facilitating the switching of transmission between "on" state (using VO2 in its semiconducting state at temperatures below its phase transition temperature T-c) and "off" state (metallic VO2 at temperatures above T-c). The PCM layer on top of the metallic VO2 layer is used either for continuously adjusting the absorption peak spectrally (by up to 1.8 mu m using different phases of Ge3Sb2Te6) or for switching between absorption mode (A = 0.99 with amorphous In3SbTe2) and reflection mode (R = 0.85 with crystalline In3SbTe2). The presented concept of merging static, non-volatile thermal switching (via PCMs) with dynamic, volatile thermal modulation (via PTMs) empowers a new generation of optical devices for smart optical switching, for example in spectrally tunable safety optical switches.