Micro-racetrack coupled-resonator optical waveguides in silicon photonic wires

Coupled-resonator optical waveguide (CROW) structures including coupled micro-racetrack resonators realized using silicon photonic wires are theoretically investigated in this paper. An accurate modelling procedure has been developed. It takes into account the differences in optical coupling between two identical resonators and between a straight waveguide (bus waveguide) and a resonator. The modelling approach is based on a mixed, very general procedure, based on the transfer matrix approach for CROW investigation, coupled mode theory in a generalized form for characterization of coupling between adjacent resonators and between bus waveguides and resonators and the full-vectorial finite element method for performing coupling coefficient calculation and waveguides modal analysis. This technique can be adopted to model a wide spectrum of different CROW structures. As an explicative example, CROW structures including three coupled micro-racetrack resonators have been investigated. A large quality factor (~7 x 10⁵) has been predicted for a proposed CROW structure when the quasi-TE mode is excited. The influence of fabrication tolerances on CROW structures has been also investigated.