Investigation On Reconfigurable Metamaterials Based On Phase Change Material GST

Metamaterials refer to artificial media that consist of periodically or nonperiodically arranged sub-wavelength unit cells and they can generate unique electromagnetic response which cannot be realized by nature materials.In recent years,metamaterials consisting of various distinct unit cells have been developing quickly to achieve electromagnetic devices with different functions.Remarkable progress has been made in perfect absorption,polarization switching,structural color generation and wavefront control.Metamaterials are conventionally passive,which means the functions are fixed after fabrication.Reconfigurable and tunable metamaterials are expected to play an important role in applications like intelligent sensing,display and zoom lens.As a phase-change material,GST can be switched between amorphous and crystalline states responding to electric,optical or thermal stimulation,and simultaneously bring about changes in optical properties.GST can keep its phase state at room temperature and it can be switched rapidly and repeatedly.In recent years,it has become a hotspot of research to realize reconfigurable metamaterials integrated with GST.In this thesis,we designed two different reconfigurable metamaterials by introducing GST.The tuning mechanisms of GST in the metamaterials were studied,and the broad application prospects of the metamaterials were discussed.The specific research contents are as follows:1.The reflection spectra from a GST film on Si O₂ substrate for different anneal temperature were measured and the optical constants of GST films were calculated by fitting the reflection spectra.2.A symmetric metamaterial absorber was proposed and the superior features in generating structural color were revealed.The physics of the structural color was explored,revealing a strategy to realize practical metamaterials with symmetric geometries for applications involving tunable structural color with wide color gamut.The structure color of the proposed metamaterial absorber can be reconstructed by the phase transition of GST layer from amorphous to crystalline.Remarkably,up to 74%and 94%of the s RGB and CMY(K)space can be obtained.This finding paves the way toward the development of practical platform for color printing and display applications.3.A novel chiral metasurface absorber structure was proposed and the superior features in reconfiguration of CD effect were demonstrated.A strong CD of about 0.75can be achieved in a prescribed spectrum.Additionally,the phase transition of GST resonators enables the quasi-linearly modification of CD strength in a broad range(from 0.03 to 0.75).Furthermore,reversible chirality of the metasurface absorber can be realized by controlling the states of the left-and right-hand GST resonators separately,leading to the readily switch of CD signal between on-,off-and reverse-state.This work is expected to play an important role in the application of tunable circular polarizers,polarization imaging and sensing.