A 1.16-μm-radius disk cavity in a sunflower-type circular photonic crystal with ultrahigh quality factor.

We present a 1.16-μm-radius disk cavity with ultrahigh quality (Q) factor by embedding the disk into a sunflower-type circular photonic crystal (CPC). The bandgap 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 an order of magnitude higher than a bare disk of the same size. The design is experimentally verified with a record high loaded Q of 7.4×10(5) measured from an optimized device fabricated on a silicon-on-insulator substrate.