Electrical Control of Multilevel Optical Reflectivity in Phase-Change Materials

Phase-change materials (PCMs) offer broadband, non-volatile, and reversible control of optical properties, making them promising candidates for reconfigurable integrated photonics. In this work, we experimentally demonstrate the electrical programming of multilevel optical reflectivity in a SiO2/GST/SiO2 thin-film stack operating in the near-infrared range. Platinum micro-heaters integrated into the structure are engineered to operate near the critical-coupling condition, enhancing reflectivity contrast during progressive crystallization of Ge2Sb2Te5 (GST). By applying voltage pulses of fixed amplitude with increasing duration and repetition, we achieve precise and gradual modulation of optical reflectivity, yielding more than 50 stable intermediate states between the amorphous and crystalline phases. These results demonstrate fine electrical control of optical properties in GST-based devices, paving the way toward scalable electro-photonic platforms for programmable metasurfaces, spatial light modulators, and neuromorphic photonics.