Lasing from a circular Bragg nanocavity with an ultra-small modal volume
  We demonstrate single-mode lasing at telecommunication wavelengths from a circular nanocavity employing a radial Bragg reflector. Ultra-small modal volume and Sub milliwatt pump threshold level are observed for lasers with InGaAsP quantum well active membrane. The electromagnetic field is shown to be tightly confined within the 300nm central pillar of the cavity. The quality factors of the resonator modal fields are estimated to be on the order of a few thousands. 
Jacob Scheuer, William M. J. Green, Guy A. DeRose, Amnon Yariv