Tunable broadband terahertz polarizer using graphene-metal hybrid metasurface

We demonstrate an electrically tunable polarizer for terahertz (THz) frequency electromagnetic waves formed from a hybrid graphene-metal metasurface. Broadband (>3 THz) polarization-dependent modulation of THz transmission is demonstrated as a function of the graphene conductivity for various wire grid geometries, each tuned by gating using an overlaid ion gel. We show a strong enhancement of modulation (up to ∼17 times) compared to graphene wire grids in the frequency range of 0.2–2.5 THz upon introduction of the metallic elements. Theoretical calculations, considering both plasmonic coupling and Drude absorption, are in good agreement with our experimental findings

The mechanism of energy transfer from Si nanocrystals to Er ions in SiO

The mechanism of energy transfer from silicon nanocrystals (Si-nc's) to erbium (Er) ions is studied by analyzing time transient of Er photoluminescence at 1.54 ${\mu}$m. It is shown that two different energy transfer mechanisms, i.e., fast and slow, exist in SiO2 films containing Si-nc's and Er ions, and that the ratio of slow to fast processes depends on size of Si-nc's and Er concentration. A quantitative analysis reveals that Er ions located within about 1.5 nm from the surface of Si-nc's are excited by the fast process, and those located within about 2.5 nm by the slow process if no Er ions exist within 1.5 nm from the surface. Er ions staying outside these regions cannot be sensitized by Si-nc's