High-Q Si microresonators formed by substrate transfer on silica waveguide wafers.

We report the first demonstration of Si microresonators (MRs) fabricated via substrate transfer on a silica waveguide (WG) wafer. Specifically, these Si microdisks were fabricated on a layer of Si (0.16-0.2 μm thick) that was directly-bonded on a silica waveguide wafer. We measured the throughput and drop spectrum of these microdisks when coupled to bonded silica waveguides, and observed loaded quality-factors (Qs) of ≥10(4). We modeled, in addition, the dispersion of whispering gallery modes in these microdisks to show phase-matched coupling with an incident silica waveguide or fiber-taper. Using the measured extinction ratio and loaded-Q, we evaluated, in addition, the coupling coefficient between the incident waveguide/taper and Si MR.