Light Phase Modulation with Transparent Paraffin‐Based Phase Change Materials

Phase change materials (PCM) have greatly contributed to optics with applications ranging from rewritable memories to smart windows. This is possible thanks to the variation in optical properties that PCMs undergo upon thermally‐induced phase change. However, this behavior is accompanied by a loss of optical transparency in one (or more) of their phases, posing a major limitation for transmission‐based functionalities. Here this challenge is addressed by producing PCM‐based composites that remain transparent in the visible spectrum during their phase transition. The cornerstone of this innovative material is the use of 30 nm‐in‐size nanoparticles of paraffin as PCMs, which minimizes the scattering within the polymer host matrix regardless of the paraffin's phase. To demonstrate the potential of this approach, it is shown that thin composite layers can modulate the phase of the incident visible light using temperature, achieving uniform phase profiles with maximum phase shifts up to π radians. Notably, the composites studied exhibit up to threefold larger phase changes for the same input power over reference thermo‐optical materials like polydimethylsiloxane. These findings position paraffin‐based composites as promising materials for various thermo‐optical applications, including wavefront shaping and aberration correction, with the potential to significantly impact a variety of optical technologies.