Broadband Measurement and Tuning of the Volatile Thermo‐Optic Properties in Chalcogenide Phase Change Materials

Chalcogenide phase change materials (PCM's) are shown to exhibit a much‐overlooked giant switchable volatile thermo‐optic response across the visible/telecommunication bands. The first broadband measurement of this is presented in the alloys: Ge 2 Sb 2 Te 5 , Sb 2 Te 3 , Sb 2 S 3, and Sb 2 Se 3 , demonstrating that their response can exceed that of many commonly used volatile reconfigurable material platforms. Additionally, it is observed that the thermo‐optic response in some PCM alloys can be uniquely switched from positive to negative sign. To engineer this response based on application requirements, phase change metacoatings are introduced, relying on subwavelength interlayer nanostructuring of the PCM layer interleaved with transparent dielectric barriers. It is demonstrated that their thermo‐optic properties can be suppressed across broad frequency ranges and tuned by varying the periodicity within the metacoating, without altering the composition or stoichiometry of the PCM layer. This shows that neglecting thermo‐optical effects in photonic platforms with PCM inclusions during device design may lead to instabilities and noise due to intrinsic thermo‐optic drifts. It also highlights the potential for exploring new PCMs/PCM heterostructures to serve as the sole modulation layer in PIC architectures, meeting both volatile and nonvolatile signal modulation needs, promising significant reductions in device footprints/power consumption in classical and emerging quantum photonic architectures.