Mode characteristics of a strongly confined square cavity suspended in air via a pedestal on the substrate are investigated by a three-dimensional finite-difference time-domain technique. The mode wavelengths and mode quality factors (Q factors) are calculated as the functions of the size of the pedestal and the slope angle θ of the sidewalls of the square slab, respectively. For the square slab with side length of 2 μm, thickness of 0.2 μm, and refractive index of 3.4, on a square pedestal with refractive index of 3.17, the Q factor of the whispering-gallery (WG)-like mode transverse-electric TE<sup>o</sup><sub>(3,5)</sub> first increases with the side length b of the square pedestal and then quickly decreases as b>0.4 μm, but the Q factor of the WG-like mode TE<sup>o</sup><sub>(4,6)</sub> drops down quickly as b>0.2 μm, owing to their different symmetries. The results indicate that the pedestal can also result in mode selection in the WG-like modes. In addition, the numerical results show that the Q factors decrease 50% as the slope angle of the sidewalls varies from 90° to 80°. The mode characteristics of WG-like modes in the square cavity with a rectangular pedestal are also discussed. The results show that the nonsquare pedestal largely degrades the WG-like modes.
© 2006 Optical Society of America
Lasers and Laser Optics
Original Manuscript: November 22, 2005
Manuscript Accepted: January 29, 2006
Qin Chen and Yong-Zhen Huang, "Investigation of mode characteristics for a square cavity with a pedestal by a three-dimensional finite-difference time-domain technique," J. Opt. Soc. Am. B 23, 1287-1291 (2006)