Nondegenerate monopole mode of single defect two-dimensional triangular photonic band-gap cavity

The two-dimensional monopole mode is investigated as a candidate for a nondegenerate photonic band-gap (PBG) cavity mode. This monopole mode formed in a single defect triangular PBG cavity is truly nondegenerate and remains nondegenerate in the sense that the introduction of asymmetry does not result in splitting of the mode. Several methods to tune the resonant frequency of the mode are studied. The radii, positions, and shapes of the nearest-neighbor air holes are varied in this analysis using the three-dimensional finite-difference time-domain calculation. The quality factor of the monopole mode formed in a slab waveguide structure is found to be larger than that of the dipole mode when the shape of the nearest-neighbor holes is elliptical.