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

Abstract 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 µm 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.