Multi-Level Optical Switching by Amorphization in Single- and Multi-Phase Change Material Structures

The optical properties of phase-change materials (PCMs) can be tuned to multiple levels by controlling the transition between their amorphous and crystalline phases. In multi-material PCM structures, the number of discrete reflectance levels can be increased according to the number of PCM layers. However, the effect of increasing the number of layers on quenching and reversibility has not been thoroughly studied. In this work, the phase-change physics and thermal conditions required for reversible switching of single and multi-material PCM switches are discussed based on thermo-optical phase-change models and laser switching experiments. By using nanosecond laser pulses, 16 different reflectance levels in Ge2Sb2Te5 are demonstrated via amorphization. Furthermore, a multi-material switch based on Ge2Sb2Te5 and GeTe with four discrete reflectance levels is experimentally proven with a reversible multi-level response. The results and design principles presented herein will impact active photonics applications that rely on dynamic multi-level operation, such as optical computing, beam steering, and next-generation display technologies. The overlooked process of partial melting is exploited to achieve continuous optical levels in a single film of the phase-change material Ge2Sb2Te5. The stability of the optical switch is improved by introducing a multi-layer structure containing materials Ge2Sb2Te5 and GeTe, with four discrete and reversible optical levels. The discussion is supported by nanosecond laser switching and multi-physics modeling.image