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High-Q whispering-gallery mode in the photonic crystal hexagonal cavity

Using the finite-difference time-domain calculations, we study whispering-gallery-like modes in photonic crystal air-bridge slab hexagonal defect cavities as good candidates for high quality-factor (Q) and small mode-volume (V) resonant modes. In the hexapole mode of a modified single-defect cavity, structural parameters are optimized to obtain very large Qs of even higher than 2 x 106 with small effective V of the order of cubic wavelength in material, the record value of theoretical Q/V. In addition, the H2-cavity whispering-gallery mode (WGM) is investigated and the defect geometry is modified to increase the Q of the WGM. By symmetrically distributing 12 nearest neighbor holes around the defect and controlling size of holes, it is possible to drastically increase the Q of >105 while preserving effective mode volume of the order of the cubic wavelength in material. We expect the WGMs in photonic crystal cavities are quite promising for low-loss photonic integrated circuit elements and high-efficiency quantum optical devices.