High-Q microcavity ring and disk resonators: FDTD analysis of resonance and coupling characteristics

Micron-size photonic and optoelectronic components can be designed end optimized using finite-difference time-domain (FDTD) solutions of Maxwell´s equations. We have developed FDTD models to characterize key optical design parameters of passive microcavity ring and disk resonators proposed for VLSI-scale photonic integrated circuits (PICs). We present FDTD-computed coupling factors, resonance frequencies, and quality factors (Q) of microcavity ring and disk resonators coupled to strongly-guiding waveguides. These structures offer high Qs and wide free spectral range. Key mechanisms which affect the Q are radiative waveguide bending loss, surface-roughness scattering loss, and the coupling between the cavity and adjacent input/output waveguides. All of these effects are included in our simulations. The strong lateral waveguide confinement due to the large contrast between the semiconductor core and air cladding allows ring and disk diameters to be as small as 2 /spl mu/m with negligible bending loss. To model the side-wall roughness, we use stepped-edge geometries in the Cartesian grid. The FDTD method naturally takes into account phase variations, which is crucial for investigating the coupling phenomenon. We also present an example of our nanofabrication results for devices designed in part with this method.