Sharp Fano Resonances From a Two-Mode Waveguide Coupled to a Single-Mode Ring Resonator

Coupling between a single-mode ring resonator and a two-mode bus waveguide is investigated theoretically and experimentally to achieve sharp resonant lineshape slopes of the difference of the two mode power transmissions. Fano-shaped output lineshapes are shown to depend on the coupling coefficients, relative power distribution, and relative phase difference of the two input modes. A device is fabricated in a polymer and silicon dioxide material system by a photolithographic process. The transmissions of the two modes are measured via on-chip add-drop mode filters. Measurements of the two-mode-coupled resonator device result in a lineshape slope of 27.1 nm^-1. The technique exploits spatial mode orthogonality to realize co-located coupling ports to the resonator. Photonic circuit layouts are simplified and the number of waveguide crossings are reduced in applications utilizing a dense array of resonators producing sharp asymmetrical Fano-shaped resonance transmissions.