Radiation rate enhancement in subwavelength plasmonic ring nanocavities

We demonstrate 25 times radiation rate and 2 times quantum efficiency enhancement of Er ions in metal-insulator-metal (MIM) ring nanocavities at room temperature. In particular, using time-resolved photoluminescence spectroscopy in partnership with full-vector numerical simulations based on the finite difference time domain (FDTD) method, we design, fabricate, and systematically investigate the photonic density of states, the quantum efficiency, and the 1.55 μm radiation dynamics of cavities with varying nanoscale active regions. Our experimental findings demonstrate that the engineering of deep subwavelength gap plasmon modes leads to dramatic Purcell enhancement even at modest cavity Q factors. Finally, we discuss the possibility of achieving lasing due to the enhancement of stimulated emission rate achievable in ring nanocavities, and we provide a perspective for Si-compatible plasmon-enhanced nanolasers.