Manipulating mid-infrared wavefront through reflective Ge3Sb2Te6 metasurfaces

Due to the increasing complexity of modern communication systems, the requirements for electromagnetic wave are becoming more and more rigorous. Traditional natural materials are not easy to integrate into tunable systems. Metasurface is a two-dimensional array, and it has a more significant advantage in electromagnetic control and attracts great attention. Here, Ge3Sb2Te6-based metasurfaces are presented to control electromagnetic wavefront by changing the state of Ge3Sb2Te6 in the mid-infrared range. Eight meta-atoms are designed to form linear phase distribution with phase difference of 45 degrees at 74 THz. When Ge3Sb2Te6 is in the amorphous state, the designed meta-atoms have low loss and high reflection. Ge3Sb2Te6 block is designed into a specific structure in a certain way, which realizes deflection of electromagnetic wavefront and vortex beam with orbital angular momentum l = 1 or l = 2. By means of convolution, anomalous reflection is combined with orbital angular momentum to form an anomalously deflected vortex beam. When the state of Ge3Sb2Te6 is crystalline, amplitudes of meta-atoms decrease and linear phase distribution is destroyed. Reflected wave becomes almost mirror reflection wave. Our design may open a pathway to novel types of metasurfaces.