Photonic quantum ring laser
  We report a quantum ring-like toroidal cavity naturally formed in a vertical-cavity-like active microdisk plane due to Rayleigh's band of whispering gallery modes. The $\sqrt{T}$-dependent redshift and a square-law property of microampere-range threshold currents down to 2 $\mu$A are consistent with a photonic quantum wire view, due to whispering gallery mode-induced dimensional reduction. 
J. C. Ahn, K. S. Kwak, B. H. Park, H. Y. Kang, J. Y. Kim, and O'Dae   Kwon