Pre- and Post-Fabrication Tuning of Bends in Microdisk CROW Sections: A Numerical Study

We present a comprehensive numerical study of light transport through bends and branches of coupled resonator optical waveguides (CROWs) composed of side-coupled wavelength-size whispering-gallery (WG) mode microdisk resonators. This study aims to reveal the underlying mechanisms of WG-mode coupling in finite-size aperiodic CROW sections. Understanding of these mechanisms offers ways to reduce CROW bend losses and to design tunable and switchable optical components based on CROWs. We show that by properly choosing the radius of the microdisk positioned at the CROW bend at the pre-fabrication design stage significant reduction of bend losses for any chosen CROW bend angle can be achieved. Furthermore, we demonstrate a possibility of using thermo-optically or electro-optically tunable microdisks for post-fabrication tuning of CROW bends and for realization of switching in branched CROW sections.