High-Q microcavities realized in a circular photonic crystal slab

A series of microcavities in circular photonic crystal slabs are studied in this paper. It is shown that high quality factors can be obtained for such microcavities. For a cavity with three inner layers of air holes missing, Q factor larger than 105 can be obtained. It is also worth noting there exists resonant modes with high quality factors, even for the defect-free circular photonic crystal slab, due to gradual change of the average effective index.