The whispering gallery modes of micro-toroid cavities have very high quality (Q) factors and small mode volumes, which can interact with single optical emitters and form ideal cavity electrodynamical systems. Such high-Q micro-cavities have also been widely used for ultra-sensitive biosensors,low-threshold and narrow linewidth lasers, frequency comb, and cavity optomechanics applicationsl. We have demonstrated low threshold micro-toroid/sphere lasers with semiconductor nanowires2 and doped rare-earth ions3 as the gain media respectively.