Vertical radiation and directional emission for metal-confined nanocylinder resonator

The mode properties of metal-coated nanocylinder resonators are numerically investigated for realizing directional emission. The metal confinement layer not only reduces the radiation loss greatly but also introduces a great metal dissipation loss. The compromise of the metal dissipation loss and the output coupling is investigated accounting the destructive interference of leakage waves. The TE and TM modes show different vertical radiation characteristics, and a thin vertically coupled waveguide is proposed for realizing unidirectional emission. Furthermore, wavelength-scale metal-confined circular and square cylinder lasers are demonstrated under optical pumping.