A 1.16-{\mu}m-radius disk cavity in a sunflower-type circular photonic   crystal with ultrahigh quality factor
  We present a 1.16-\mum-radius disk cavity with ultrahigh quality (Q) factor by embedding the disk into a sunflower-type circular photonic crystal (CPC). The band gap of the CPC reduces the bending loss of the whispering-gallery mode of the disk, leading to a simulated Q of 10^7, at least one order of magnitude higher than a bare disk of the same size. The design is experimentally verified with a record high loaded Q of 7.4 \times 10^5 measured from an optimized device fabricated on a silicon-on-insulator substrate. 
Xufeng Zhang, Xiankai Sun, and Hong X. Tang
physics.optics