Reversible Optical Switching of Infrared Antenna Resonances with Ultrathin Phase-Change Layers Using Femtosecond Laser Pulses

Abstract

Recently, phase-change materials (PCMs) have gained a lot of interest in the field of active metamaterials and plasmonics due to their switchable optical properties. In the infrared spectral range the huge contrast in the refractive index between an amorphous and a crystalline phase can be employed for nonvolatile tuning of nanoantenna or metasurface resonances. To make use of such concepts in devices, the reversible switching of the active material has to be realized. Here we demonstrate such reversible cycling by applying femtosecond pulses from a Ti:sapphire laser. These optical pulses trigger the phase transitions of the PCM thin film, which is covering infrared nanoantennas. Ge3Sb2Te6 is chosen as the PCM, since it offers very low losses in the infrared spectral range. The layer geometry presented is exceptionally thin (∼1/50 of the operating wavelength) and the design intentionally avoids lossy capping layers. Infrared reflectivity measurements verify the laser-induced resonance shifts of the plasmonic nanoantenna arrays. This switching mechanism opens the possibility to optically perform active, reversible, and nonvolatile tuning of metasurfaces.