Silicon Polygonal Microdisk Resonators

We show silicon polygonal microdisk resonators with laterally coupled waveguides. Our two-dimensional (2-D) finite-difference time-domain (FDTD) simulations and spatial Fourier analysis reveal that waveguide coupling to a planar microstructure with a sufficiently long and flat coupling sidewall enables directional wave vector coupling in the microstructure. Similar analysis shows that waveguide coupling to a polygonal microresonator flat sidewall enables preferential coupling to only a few resonance modes in large-sized polygonal microresonators. Our experiments on silicon waveguide-coupled 50-mum octagonal microresonators demonstrate only two dominant modes, with a Q of about 10 ⁴ and an extinction ratio (ER) of about 15 dB. We also demonstrate square and hexagonal silicon microresonators with nearly single dominant modes, a Q of the order of 10³, and an ER exceeding 10 dB